Duramed Pharmaceuticals, Inc., and Barr Laboratories, Inc.; Conjugated Estrogens Tablets; Proposal to Refuse to Approve Two Abbreviated New Drug Applications; Opportunity for a Hearing

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Food and Drug Administration

[Docket No. 97N-0325]

Duramed Pharmaceuticals, Inc., and Barr Laboratories, Inc.;

Conjugated Estrogens Tablets; Proposal to Refuse to Approve Two

Abbreviated New Drug Applications; Opportunity for a Hearing

AGENCY: Food and Drug Administration, HHS.

ACTION: Notice.

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SUMMARY: The Center for Drug Evaluation and Research (CDER) is

proposing to refuse to approve two abbreviated new drug applications

(ANDA's) for synthetic conjugated estrogens tablets. Conjugated

estrogens tablets are intended for estrogen replacement to treat

symptoms of menopause or to prevent osteoporosis. ANDA 40-115

(Cenestin, conjugated estrogens tablets, 0.3 milligrams (mg), 0.625 mg,

0.9 mg, 1.25 mg, and 2.5 mg) has been submitted by Duramed

Pharmaceuticals, Inc., 5040 Lester Rd., Cincinnati, OH 45213 (Duramed).

ANDA 40-154 (conjugated estrogens tablets, 0.625 mg and 1.25 mg) has

been submitted by Barr Laboratories, Inc., 2 Quaker Rd., Pomona, NY,

10970 (Barr). Food and Drug Administration (FDA) is offering Duramed

and Barr an opportunity for a hearing on the proposal. The primary

basis for CDER's proposed refusal to approve the ANDA's is the agency's

conclusion that there is insufficient information to show that the

active ingredients of synthetic conjugated estrogens tablets are the

same as the active ingredients of the reference listed drug.

DATES: A hearing request is due on or before September 8, 1997; data

and information in support of the hearing request are due on or before

October 6, 1997.

ADDRESSES: A request for hearing, supporting data, and other comments

are to be identified with Docket No. 97N-0325 and submitted to the

Dockets Management Branch (HFA-305), Food and Drug Administration,

12420 Parklawn Dr., rm. 1-23, Rockville, MD 20857.

FOR FURTHER INFORMATION CONTACT: Carol E. Drew, Center for Drug

Evaluation and Research (HFD-7), Food and Drug Administration, 5600

Fishers Lane, Rockville, MD 20857, 301-594-2041.

SUPPLEMENTARY INFORMATION:

I. Background

Both Duramed and Barr have submitted ANDA's for synthetic

conjugated estrogens tablets intended for estrogen replacement to treat

symptoms of menopause or to prevent osteoporosis. The reference listed

drug for this product is Premarin, manufactured by Wyeth-Ayerst, and

derived from a natural source material, the urine of pregnant mares.

On September 26, 1994, Duramed submitted ANDA 40-115 for Cenestin

(conjugated estrogens tablets) under section 505 (j) of the Federal

Food, Drug, and Cosmetic Act (the act) (21 U.S.C. 355(j)). Duramed

filed amendments to this ANDA on March 7 and 25, 1996; April 2 and 3,

1996; May 9 and 14, 1996; June 28, 1996; July 12, 1996; August 14, 15,

19, and 29, 1996; October 8 and 9, 1996; December 17, 1996; January 23

and 31, 1997; and February 14, 1997. On May 5, 1997, in accordance with

Sec. 314.120 (21 CFR 314.120), CDER notified Duramed by letter that

Duramed's ANDA was not approvable under section 505 (j)(2)(A)(ii)(II)

and (j)(3)(C)(ii) because the ANDA was insufficient to show that the

active ingredients of the proposed generic drug product were the same

as the active ingredients of the reference listed drug.

On July 20, 1995, Barr submitted ANDA 40-154 for conjugated

estrogens tablets under section 505(j) of the act. Barr filed

amendments to this ANDA on May 13, 1996, and November 14 and 18, 1996.

On May 5, 1997, in accordance with Sec. 314.120, CDER notified Barr by

letter that Barr's ANDA was not approvable under section 505

(j)(2)(A)(ii)(II) and (j)(3)(C)(ii) of the act because the ANDA was

insufficient to show that the active ingredients of the proposed

generic drug product were the same as the active ingredients of the

reference listed drug.

CDER attached a detailed memorandum to the not approvable letters

issued to both Duramed and Barr. This memo, from the CDER Director to

the Director of the Office of Generic Drugs, outlined the legal and

scientific rationale for CDER's position that a synthetic generic

version of Premarin should not be approved until the active ingredients

of Premarin have been sufficiently well defined to permit an ANDA

applicant to show that a synthetic generic form of Premarin has the

same active ingredients. In the not approvable letters of May 5, 1997,

CDER notified Duramed and Barr that they each had the option to amend

or withdraw their respective ANDA's under Sec. 314.120, or request an

opportunity for a hearing under Sec. 314.200 (21 CFR 314.200).

In response to CDER's not approvable letter, Duramed submitted an

initial response on May 15, 1997, and under Sec. 314.120(a)(5),

requested a 30-day extension of time to respond pending review by its

scientific and medical personnel of the not approvable letter and other

information.

In a letter dated June 13, 1997, Duramed requested the opportunity

for a hearing under Sec. 314.120(a)(3) on the question of whether there

are grounds for denying approval of ANDA 40-115.

On June 26, 1997, CDER issued a response to Duramed's May 15, 1997,

letter documenting CDER's decision to honor Duramed's request for an

extension contingent upon Duramed's agreement, under

Sec. 314.120(a)(3), that CDER would have until August 8, 1997, to give

written notice of an opportunity for a hearing to Duramed, under

Sec. 314.200, on the question of whether there are grounds for refusing

to approve the ANDA.

On May 15, 1997, Barr submitted a letter to FDA requesting a 60-day

extension to respond to the not approvable letter dated May 5, 1997. On

July 3, 1997, CDER issued a letter granting Barr's May 15, 1997,

request for an extension contingent on Barr's agreement that FDA would

have 50 days from the date of Barr's request for the opportunity for a

hearing to provide written notice of an opportunity for a hearing. Barr

submitted a letter to FDA on July 7, 1997, requesting an opportunity

for a hearing on the not approvable letter and agreeing to the

condition that FDA would have 50 days from July 7, 1997, to respond.

This notice includes CDER's proposed order to refuse to approve the

Barr and Duramed ANDA's for synthetic conjugated estrogens drug

products and responds to both Duramed's and Barr's requests for an

opportunity for a hearing on the question of whether there are grounds

for refusing to approve those ANDA's.

[[Page 42563]]

II. Regulatory History of Conjugated Estrogens

FDA first permitted a new drug application for Premarin to become

effective in 1942 under the new drug provisions of the act (Pub. L. 75-

717, 52 Stat. 1040 (1938)), based on chemistry, manufacturing, and

controls information acceptable at that time and a showing, from

reports of clinical investigations, that the drug product was safe for

its intended use in the treatment of menopausal symptoms and related

conditions. The product was known at that time to contain estrone and

equilin, and it was known that additional estrogens were present in

smaller amounts. The tablet strengths and estrogenic potencies of

Premarin tablets were controlled using a colorimetric assay and a rat

bioassay, respectively, with estrone as the reference standard. Thus,

the 0.625 mg Premarin tablet was assigned this value because it

contained estrogenic potency that, in the rat model, was equivalent to

0.625 mg of sodium estrone sulfate.

In 1970, the United States Pharmacopeia (USP) published monographs

for conjugated estrogens and conjugated estrogens tablets, establishing

the first compendial standards for these products (Ref. 1). The USP

described conjugated estrogens as containing sodium estrone sulfate and

sodium equilin sulfate.1 This description appears to have

been based on the known quantity, in Premarin, of each of the two

ingredients as well as their demonstrated clinical estrogenic effects

(Refs. 2, 3, and 4). The two compounds were known to be the most

abundant estrogens in Premarin. Clinical data showing estrone to be an

active estrogen were available, and small-scale clinical studies of

sodium equilin sulfate indicated that it was a more potent estrogen

than estrone (Ref. 6). Limited data from a study completed in 1963 and

published in 1971 suggested that sodium 17-dihydroequilin

sulfate, the third most abundant estrogen, had little clinical activity

(Ref. 6).

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\1\ In the preamble to the final rule implementing Title I of

the Drug Price Competition and Patent Term Restoration Act of 1984,

FDA stated that, although in most cases the agency will consider an

active ingredient to be the same as that of the reference listed

drug if it meets the standards of identity described in the USP,

``in some cases, FDA may prescribe additional standards that are

material to an ingredient's sameness.'' (See 57 FR 17950 at 17959,

April 28, 1992). See also Sec. 320.1(c) (21 CFR 320.1(c)), which

states that an identical active drug ingredient may meet ``identical

compendial or other applicable standards'' (emphasis added). FDA

applies current scientific knowledge in making its regulatory

decisions, even if that knowledge has not yet been incorporated into

the USP monograph.

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With the publication of the monographs in 1970, the rat potency

test was eliminated and replace by a chemical assay for the two active

ingredients. However, the traditional strength assignment was

maintained, even though the tablets contained fewer milligrams of

sodium estrone sulfate and sodium equilin sulfate than the milligram

dose stated on the label.

In 1972, FDA published an assessment of the effectiveness of

Premarin (Ref. 7). Drugs such as Premarin that were approved prior to

1962 were required to demonstrate safety but not effectiveness at the

time of approval. In 1962, enactment of the Harris-Kefauver amendments

to the act created a requirement for a demonstration of the

effectiveness of new drugs including new drugs approved between 1938

and 1962 (Pub. L. 87-781, 76 Stat. 780). FDA contracted with the

National Academy of Sciences/National Research Council to carry out the

Drug Efficacy Study to assess the evidence of effectiveness available

for new drugs approved prior to 1962. FDA then implemented the results

in an effort known as the Drug Efficacy Study Implementation (DESI).

The 1972 Federal Register notice announced FDA's conclusion that a

number of estrogen products, including Premarin, had been shown to be

effective for menopausal symptoms (and several other conditions) based

on the DESI Panel recommendations and other available evidence. FDA

also found that the listed estrogen products were ``probably

effective'' for prevention of osteoporosis. For indications found to be

``probably effective,'' FDA required sponsors to either submit

substantial evidence of effectiveness or remove the indication from the

product labeling within a certain period of time.

In 1978, Ayerst Laboratories proposed that conjugated estrogens be

required to contain seven estrogenic components. Ayerst subsequently

modified this proposal to request only that 17-dihydroequilin

be added to the existing USP monograph (Ref. 8). In 1982, FDA and USP

convened a public meeting to discuss Ayerst Laboratories' proposal that

the monograph for conjugated estrogens include 17-

dihydroequilin (Ref. 9). FDA stated at that time that the composition

of conjugated estrogens should be determined by estrogenic potency and

that the proposed compound had low potency and likely did not

contribute to the clinical effect. USP determined that 17-

dihydroequilin should not be added to the monograph as an active

ingredient.

In 1980, FDA published the first version of the document now known

as the Approved Drug Products with Therapeutic Equivalence

Determinations, also known as the ``Orange Book'' (Ref. 10). This

document lists the FDA assignment of therapeutic equivalence among

duplicate drug products based on available data pertaining to their

pharmaceutical equivalence and bioequivalence. Existing conjugated

estrogens tablet products were classified as ``BS,'' i.e., not

considered therapeutically equivalent, because of concern that the USP

monograph specifications for estrone sulfate and equilin sulfate were

inadequate to ensure that products meeting the monograph standard would

necessarily produce equivalent therapeutic effects in patients (Ref.

11). The ``BS'' code is used by FDA to indicate that drug products are

not considered therapeutic equivalents due to deficient drug standards.

In 1986, FDA announced in the Federal Register that a 0.625 mg dose

of Premarin daily was found to be effective for prevention of

osteoporosis in postmenopausal women (Ref. 12). Two dose-response

studies evaluating the effect of Premarin on bone mineral density had

been published in the literature (Refs. 13 and 14).

In 1986, while developing an appropriate in vitro dissolution test

standard for conjugated estrogens bioequivalence testing, FDA

discovered that Premarin tablets were a modified release dosage form

(Ref. 15). This unexpected characteristic of the Premarin formulation

meant that generic copies were unlikely to be bioequivalent unless they

also had similar modified release characteristics. Because of this

discovery, FDA changed the Orange Book code for generic conjugated

estrogens tablets from ``BS'' to ``BP'' (Ref. 16). The code ``BP''

means that generic products so labeled are not considered

therapeutically equivalent due to a potential bioequivalence problem.

FDA then began to require that generic conjugated estrogens products

demonstrate bioequivalence through in vivo human subject bioequivalence

testing (Ref. 17). Because bioequivalence testing is ordinarily

performed on the active ingredients of a product, the question of the

active ingredients of Premarin again was raised.

In 1989, FDA's Fertility and Maternal Health Drugs Advisory

Committee considered the question of the active ingredients in Premarin

(Ref. 18). The Committee agreed that sodium estrone sulfate and sodium

equilin sulfate are active ingredients, but could not reach a consensus

on whether or not other

[[Page 42564]]

estrogens in Premarin were active ingredients (Ref. 19). In 1990, an Ad

Hoc Subcommittee of the Fertility and Maternal Health Drugs Advisory

Committee met to consider Premarin bioequivalence issues (Ref. 20).

Again, the group agreed that the two named active ingredients were

correctly designated, but could not reach a consensus on whether

additional components should be regarded as active ingredients (Ref.

21).

In 1990, FDA published a proposal to withdraw approval of the

``BP'' coded generic conjugated estrogens formulations for which

therapeutic equivalence could not be ensured (Ref. 22). The proposal

included withdrawing all generic conjugated estrogens marketed at that

time. The agency withdrew approval for these products in 1991, and

there are currently no approved generic conjugated estrogens tablets on

the U.S. market (Refs. 23 and 24).

In February 1991, FDA's Generic Drugs Advisory Committee met to

consider issues of pharmaceutical equivalence and bioequivalence for

conjugated estrogens (Ref. 25). FDA proposed to the committee that

three of the additional estrogens in Premarin be recommended for

inclusion as ``concomitant components'' in the USP monograph for

conjugated estrogens (Refs. 26 and 27). These particular ``concomitant

components'' would be required to be in the product, but would not be

considered active ingredients and, thus, would not need to be included

in bioequivalence testing (Ref. 28). The Generic Drugs Advisory

Committee endorsed this proposal (Ref. 29). Subsequently, the USP

monographs on conjugated estrogens were amended to include the three

additional ``concomitant components'' (Ref. 30).

On November 30, 1994, Wyeth-Ayerst submitted a citizen petition

requesting, among other things, that FDA not approve any generic

conjugated estrogens products that do not contain the compound sodium

``8,9-dehydroestrone sulfate (DHES) (Ref. 31). Wyeth-Ayerst also

submitted a petition for a stay of action requesting that FDA stay any

decision to ``receive'' an ANDA for a conjugated estrogens product that

does not contain DHES and stay any approval of such an application

until FDA responds to the petition (Ref. 32).

Because of the complex scientific issues associated with

determining the active ingredients of conjugated estrogens, in the

summer of 1995, CDER formed an Ad Hoc Conjugated Estrogens Working

Group to consider these issues. That group of CDER staff examined

available data related to the composition of conjugated estrogens and

prepared a background document for the Fertility and Maternal Health

Drugs Advisory Committee.

On July 27 and 28, 1995, FDA's Fertility and Maternal Health Drugs

Advisory Committee, with representation from FDA's Generic Drugs

Advisory Committee and FDA's Endocrinologic and Metabolic Drugs

Advisory Committee, heard presentations and discussions on the

composition of conjugated estrogens (Ref. 33). At the end of the

deliberations, in answer to questions regarding what additional

components, if any, beyond the two recognized active ingredients

contribute to the clinical safety and effectiveness of Premarin, the

Committee voted unanimously in favor of the following statement:

The Committee feels that insufficient data were presented to

determine whether or not any individual component of Premarin or any

combination of components in Premarin other than estrone sulfate and

equilin sulfate must be present in order for Premarin to achieve its

established levels of efficacy and safety [emphasis added].

(Ref. 34).

On November 1, 1996, FDA completed a ``Preliminary Analysis of

Scientific Data on the Composition of Conjugated Estrogens' (Ref. 35).

On May 1, 1997, the Ad Hoc Conjugated Estrogens Working Group

completed its final report providing a scientific clarity background

for CDER's decision regarding the composition of conjugated estrogens

(Ref. 36).

The regulatory history of conjugated estrogens reflects the

complexity of the scientific issues involved. FDA's positions on these

issues have evolved over time as new information has become available.

As with any such complicated scientific issue, differences in

scientific opinion arose and continue to exist concerning how available

data are to be interpreted and applied in the regulatory context. These

differing views (Refs. 37, 38, and 39) were considered prior to this

proposed order refusing to approve the two ANDA's for synthetic

conjugated estrogens identified above.

III. The Deficiencies in ANDA 40-115 and ANDA 40-154

The primary basis of this proposed order refusing to approve ANDA

40-115 and ANDA 40-154 is that these ANDA's fail to provide sufficient

information to show that the active ingredients of the proposed generic

drug products are the same as the active ingredients of the reference

listed drug. Below is a summary of the applicable legal requirements

and a detailed statement on the scientific basis for CDER's conclusion

that the ANDA's fail to show that the active ingredients of the

proposed generic drug products are the same as those of the reference

listed drug.

A. Legal Requirements

Under section 505(j)(2)(A)(ii)(II) of the act, an ANDA for a drug

product with more than a single ingredient must include information to

show that the active ingredients of the drug that is the subject of the

ANDA are the same as those in the reference listed drug, except for any

different active ingredient for which a petition was approved under

section 505(j)(2)(c) of the act. Furthermore, under section

505(j)(3)(J) of the act and Sec. 314.127(a)(12) (21 CFR

314.127(a)(12)), FDA is required to refuse to approve any ANDA that

fails to include such information. In addition, under

Sec. 314.127(a)(3)(ii), which implements section 505(j)(3)(C)(ii) of

the act, FDA is required to refuse to approve an ANDA if ``information

submitted with the abbreviated new drug application is insufficient to

show that the active ingredients are the same as the active ingredients

of the reference listed drug.''

Under 21 CFR 314.92(a)(1), the term ``same as'' is defined as

``identical in active ingredient(s)'' (Ref. 40). The term ``active

ingredient'' is defined under 21 CFR 60.3(b)(2) and 210.3(b)(7) as

follows:

[A]ny component that is intended to furnish pharmacological

activity or other direct effect in the diagnosis, cure, mitigation,

treatment, or prevention of disease, or to affect the structure or

any function of the body of man or other animals.

In the context of ANDA approvals, a generic product with the same

active ingredients as the reference listed drug that is shown to be

bioequivalent is approved without independent effectiveness

data.2 To meet the definition of an active ingredient, a

component must be intended to furnish sufficient pharmacological

activity, or other direct effect, to have some therapeutic effect

(i.e., to diagnose, cure, mitigate, treat, or prevent disease, or to

affect the structure or function of the body). An active ingredient

performs a drug's therapeutic functions. The definition of

``pharmaceutical

[[Page 42565]]

equivalents'' in Sec. 320.1(c) is consistent with this definition of

active ingredient in that it focuses on the therapeutic moiety:

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\2\ In enacting the Drug Price Competition and Patent Term

Restoration Act of 1984, Congress intended that no safety or

effectiveness data beyond that developed by the innovator company be

needed to support approval of the generic product. (See H. Rept. 857

(Part I), 98th Cong., 2d sess. 14, 16-17 (1984).) The interpretation

of the active ingredient definition in this notice is intended

solely as applied to ANDA approval.

Pharmaceutical equivalents means drug products that contain

identical amounts of the identical active drug ingredients, i.e.,

the same salt or ester of the same therapeutic moiety * * * that

meet identical compendial or other applicable standard of identity,

strength, quality, and purity, * * * disintegration times and/or

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dissolution rates.

Consequently, not all components that ``furnish pharmacological

activity or other direct effect'' meet the definition of an active

ingredient. A component may be considered an active ingredient only if

it provides a clinically meaningful contribution to the therapeutic

effect of the drug. A subjective intent for a component to have such

effect will not suffice in the absence of objective evidence of a

clinically meaningful contribution. (Cf. 21 CFR 201.128 (defining

intended use).) In most cases it will be clear what components of a

drug make clinically meaningful contributions to the drug's therapeutic

effects and, therefore, are the drug's active ingredients. However,

where FDA has determined there is sufficient evidence that a component

in the reference listed drug may make a clinically meaningful

contribution to the therapeutic effect, the agency cannot approve a

synthetic generic version of the drug that does not include such

component until it has been determined whether the component makes such

a contribution.

As discussed below, Duramed's ANDA 40-115 and Barr's ANDA 40-154

provide insufficient information to show that the active ingredients of

their conjugated estrogens tablets are the same as the active

ingredients of the reference listed drug, Premarin.

B. Active Ingredients of Premarin Are Not Fully Characterized

1. CDER's Historical Position on the Active Ingredients of Premarin

Although FDA's Scientific Advisory Committees were unable to

provide definitive advice on this issue, FDA continued to support the

position taken in the 1970 USP monograph (Ref. 41) that the ingredients

sodium estrone sulfate and sodium equilin sulfate are the sole active

ingredients in Premarin. The reasons for this position follow below

(Ref. 42).

Scientific belief had been that all estrogens were similar in their

pharmacologic actions on the body, i.e., ``an estrogen is an

estrogen.'' Therefore, it was thought that the pharmacologic activity

of an estrogen preparation could be described in terms of its total

estrogenic potency. It was believed that the effects of different

estrogens in a mixture were additive and that the identity of the

particular estrogen contributing the estrogenic potency was not

crucial. Epidemiologic data did not reveal safety or effectiveness

differences among various estrogen preparations used for hormone

replacement therapy.

As a result, Premarin had historically been defined in terms of

total estrogenic potency rather than the sum of the potencies of

various components. In 1970, when the first USP monograph was

published, little information was available on the effects of estrogens

on bone, and the estimates of estrogenic potency of Premarin components

were derived from clinical studies of menopausal symptoms. Much of

Premarin's estrogenic potency for menopausal symptoms can be attributed

to the effects of estrone and equilin.

Available data on the detailed composition of Premarin and the

pharmacologic activity of its components were limited. Much of the

available data indicated that many compounds found in Premarin were

present in small amounts and had weak estrogenic activity.

Based on the results of early studies, including studies of

Premarin, the effects of estrogen on bone mineral density appeared to

have a very steep dose-response relationship, and the 0.625 mg dose of

Premarin appeared to be near the top of the dose-response curve.

Therefore, it was believed that small differences in the estrogenic

potency of conjugated estrogens preparations, resulting from omission

of components from generic copies, would not be clinically meaningful.

In addition, the monograph ranges for the content of sodium estrone

sulfate and sodium equilin sulfate in conjugated estrogens are wide

(Ref. 43). Therefore, it was believed that minor differences in

estrogen content between synthetic generic products and Premarin due to

the absence in the generic copies of several minor Premarin

constituents could not make a clinically meaningful difference.

Note: the percent coefficient of variation of sodium estrone

sulfate is 1.98, and of sodium equilin sulfate is 3.01, based on

percent estrogen composition in 500 batches of Premarin Tablets (Ref.

44).

2. CDER's Current Position on Premarin's Active Ingredients

CDER's current position on Premarin's active ingredients is that

Premarin is not sufficiently characterized at this time to determine

all of its active ingredients, for the reasons that follow below.

Emerging scientific evidence demonstrates that all estrogens do not

exert their effects in a uniform manner with respect to different

target tissues. These differential effects may be due to variable

pharmacokinetics, 3 tissue metabolism, tissue-specific

receptor factors, or additional reasons (Refs. 45, 46, 47, 48, 49, and

50). For example, clinical studies have shown that the potency of

equilin sulfate relative to estrone sulfate varies depending on the

pharmacodynamic 4 effect being studied (Refs. 6 and 51). A

dose of equilin sulfate that is equipotent to estrone sulfate using one

parameter may be more or less potent when evaluated using a different

measure. For this reason, the active ingredients of Premarin cannot be

defined solely in terms of overall estrogenic potency in any single

system, but must be defined based on their contributions to particular

estrogenic effects.

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\3\ Pharmacokinetics can be defined as drug absorption,

excretion, metabolism, or distribution.

\4\ Pharmacodynamics can be defined as a pharmacologic or

clinical response to a given concentration [of a drug] in blood or

other tissue (58 FR 39406 at 39409 (July 22, 1993)).

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Put simply, the new scientific evidence shows that one estrogen can

be more active than another in a specific tissue or organ, such as

breast, uterus, or bone. The most striking example of this is the

synthetic estrogen analog tamoxifen, which blocks estrogen actions in

breast tissue, but has estrogen-like activity on bone. These new

findings have stimulated extensive research into new pharmaceuticals

that could have selective actions on specific tissues and thus might

provide beneficial hormone replacement therapy without some of the

undesirable side effects, or could be useful in the treatment of cancer

or other conditions.

Compositional analysis of Premarin using modern analytical

techniques demonstrates that it consists of a mixture of a substantial

number of compounds with potential pharmacologic activity. In fact, the

steroidal content of Premarin has not been completely defined (Ref.

52). Undoubtedly, many of the compounds present in Premarin do not

provide a clinically meaningful contribution to the therapeutic effects

of the drug and are best thought of as impurities. However, the

clinical tests, on which the findings of the safety and efficacy of

Premarin were based, were performed on the entire mixture, not on

individual components. A basic understanding of the chemical

composition of Premarin must be achieved as a first step in

[[Page 42566]]

adequately characterizing the product unless a complete understanding

of which components provide a meaningful clinical contribution to the

effects of the product is achieved by clinical trials alone.

Clinical studies have revealed that the assigned potencies of

Premarin tablets, which were based on the rat bioassay, do not

correctly reflect the tablets' relative potencies in human studies

(Refs. 6, 50, 51, and 53). For example, clinical studies have shown

that Premarin is between 1.4 and 2.5 times more potent than estrone

sulfate for suppression of follicle-stimulating hormone (FSH) and

menopausal symptoms in postmenopausal women (Refs. 6 and 50). Because

the human studies evaluating the relative potency of Premarin have been

small, a precise estimate of the estrogenic potency of Premarin

relative to estrone sulfate has not been determined. Because the

relative potencies of Premarin, estrone sulfate, and equilin sulfate

are not clearly established, it is not possible to tell how much of the

effect of Premarin can be accounted for by the effects of equilin

sulfate and estrone sulfate. Measuring these effects is further

complicated by the fact that the importance or contribution of each

ingredient may depend on the tissue that is being tested, e.g., bone,

breast, pituitary, or uterus.

New clinical studies have clearly demonstrated that there is a

dose-response relationship between estrogen administration and bone

mineral density in postmenopausal women (Refs. 54 and 55). It follows

that ensuring an equivalent estrogenic potency is important in the

approval of generic copies of estrogen products intended for prevention

of osteoporosis. In other words, it is important for the osteoporosis

indication that synthetic generic conjugated estrogens based on

Premarin have estrogenic strength that is identical to the Premarin

tablet.

The recent findings with regard to 8,9-dehydroestrone

sulfate (DHES) illustrate a number of the above points. This compound

was first detected in Premarin in 1975 (Refs. 56 and 57). DHES

represents only a small percentage of the estrogenic compounds present

in the product: 4.4 percent of the ``label claim'' (i.e., 4.4 percent

of 0.625 mg or approximately 0.0275 mg of DHES per 0.625 mg tablet).

(Note: Premarin also contains a small amount of the DHES metabolite

sodium 17-8,9-dehydroestradiol sulfate (Ref. 58).

This metabolite comprises approximately 0.003 mg per 0.625 mg tablet.

Therefore, the total DHES plus sodium 17-8,9-

dehydroestradiol sulfate content of a 0.625 mg tablet is about 0.03 mg

or approximately 5 percent of label claim.) Until recently little has

been known about DHES or sodium 17-8,9-

dehydroestradiol sulfate.

Pharmacokinetic studies submitted by Wyeth-Ayerst demonstrate that,

after single or repeated oral dosing of Premarin in women, the plasma

concentrations or areas under the curve (AUC's) of the (conjugated plus

unconjugated) 17-8,9-dehydroestradiol metabolite of

DHES are the same order of magnitude as the concentration of the

17-diol metabolites of the active ingredients estrone and

equilin (Refs. 59, 60, and 61). The 17 8,9-estradiol

concentration is approximately 34 percent of the combined

concentrations of the 17-diol metabolites of estrone and

equilin, or 26 percent of the 17-diol metabolites from the

three estrogens. The finding that a low-level (5 percent) component of

the tablet would generate a significant concentration of a potentially

active metabolite was completely unexpected and illustrates the

longstanding inadequate characterization of Premarin. These

pharmacokinetic data do not themselves prove that the DHES in Premarin

makes a clinically meaningful contribution to the therapeutic effect of

Premarin. However, preliminary clinical studies indicate that the

potency of DHES may be similar to that of equilin. (See detailed

discussion below.)

Based on this new scientific information, CDER concludes that

Premarin is not adequately characterized and that, therefore, at this

time, its active ingredients cannot be fully determined. Additional

information on both composition and relative potencies of components

will be necessary to adequately characterize this product. This

conclusion is in agreement with the findings of FDA's Fertility and

Maternal Health Advisory Committee at its July 27 and 28, 1995, meeting

on this subject (Ref. 33).

3. Unresolved Issues Concerning the Current Characterization of

Premarin

At the time of marketing, products such as Premarin, that are

derived from natural source material, frequently are not characterized

as completely as synthetic products would be. The term ``adequate

characterization'' is intended to mean an amount of scientific

information on a product that is sufficient to determine what

constituents in the product are responsible for making clinically

meaningful contributions to its therapeutic effects. In other words, it

is possible to define the active ingredients of a product that is

adequately characterized.

There are at least two possible ways to characterize a product. The

most straightforward method includes, first, chemical analysis to

determine what components are present at significant levels in the

product. The interpretation of ``significant levels'' cannot be exact

and would depend on the specific product; however, it is desirable that

components present at the 0.1 percent level or greater be identified

and quantified. Once the components of the product are identified, the

next step in characterization would be to determine which of them have

potential human pharmacologic activity. Such a determination may be

based on the following: The quantitative amount in the product,

structure-function relationships, in vitro tests, animal studies, human

studies, or a combination of these. Finally, for components that may

contribute to the therapeutic effect based on potential pharmacologic

activity, a study could be conducted comparing the effects of each

component alone, and in combination with additional components, to the

effects of the entire product, to demonstrate that the ``candidate''

components achieved all of the therapeutic effects of the product.

Alternatively, in cases where there is some confidence that the

``candidate'' active ingredients have all been identified, even though

the product is not fully chemically characterized, a head-to-head

comparative dose-response clinical trial(s) comparing the effects of

the combined ``candidate'' active ingredients against the original

product could, if carried out carefully, demonstrate that the

combination contributed all the clinically meaningful therapeutic

effects of the original product. This approach might not clearly

identify which of the ``candidates'' were actually active, but could

ensure that the combination tested included all of the active

ingredients in the product.

The following sections discuss the available scientific evidence on

the characterization of Premarin.

a. Composition of Premarin. At least ten estrogenic compounds have

been identified and quantified in Premarin. The composition data for

the 10 estrogenic compounds cited in the Conjugated Estrogens USP

monograph, and listed in Table 1, were generated by CDER's Division of

Drug Analysis from an analysis of 2 batches of Premarin

[[Page 42567]]

0.625 mg tablets (Ref. 62). These results agree generally with other

data available to CDER.

Table 1.--Composition Data for 10 Estrogenic Compounds

------------------------------------------------------------------------

Sodium estrogen sulfate Mg/tablet

------------------------------------------------------------------------

Estrone..................................................... 0.370

Equilin..................................................... 0.168

17-Dihydroequilin.................................. 0.102

17-Estradiol....................................... 0.027

17-Dihydroequilin.................................. 0.011

l7-Dihydroequilenin................................ 0.011

17-Dihydroequilenin................................ 0.021

Equilenin................................................... 0.015

17-Estradiol....................................... 0.005

8,9-dehydroestrone................................. 0.026

------------------------------------------------------------------------

Additional information on the component DHES and its metabolite are

discussed below. Additionally, the fact that Premarin contains

progestational agents (composition unspecified) has been disclosed by

Wyeth-Ayerst (Ref. 63). It is known that Premarin also contains

additional steroidal compounds (Ref. 52). However, precise data on

Premarin's composition are currently very limited (Refs. 64, 65, 66,

and 67).

Detailed analytical information on Premarin's composition is the

necessary basis for adequate characterization of the product. Obtaining

this information is feasible. The constituents of Premarin are small

molecules that can be fully characterized by analytical chemistry,

unlike the macromolecular constituents of most biological products,

which are difficult to fully characterize due to biologic variability.

It is desirable that the components present in Premarin at or above 0.1

percent be characterized and their biological activities determined

(Ref. 68).

It has been argued that DHES cannot be considered an active

ingredient of Premarin because its presence in and percent composition

of the formulation are not specifically controlled during the

manufacturing process (Ref. 69). Wyeth-Ayerst has submitted data

demonstrating that DHES is present at about 4.4 percent of label claim

with a range of 4.0 to 5 percent (based on 10 lots of 0.625 mg Premarin

tablets) (Ref. 70). It is desirable that any active ingredients, once

identified, be controlled during the manufacturing process.

b. Pharmacokinetics. Pharmacokinetic data on Premarin components

are presented in the FDA report entitled ``A Pharmacokinetic Analysis

of Conjugated Estrogens Including 8,9 Dehydroestrone and

17-8,9 Dehydroestradiol,'' dated October 25, 1996

(OCPB Report) (Ref. 71), and its addendum dated February 12, 1997

(Addendum) (Ref. 72), and also in information submitted to the docket

of the Wyeth-Ayerst citizen petition (Refs. 59 and 60). The OCPB Report

details plasma concentrations of estrone sulfate, equilin sulfate,

DHES, and their metabolites, as well as concentrations of 17-

dihydroequilin, after ingestion of various doses of Premarin (Ref. 72).

Additional pharmacokinetic data on Premarin components and metabolites,

presented in Addendum 2, dated March 31, 1997, to the OCPB Report (Ref.

73), and also in information submitted to the docket by Wyeth-Ayerst on

March 11, 1997 (Ref. 61), confirm the original finding discussed in the

OCPB Report.

Table 2 is derived from pharmacokinetic data submitted by Wyeth-

Ayerst based on 7-day dosing of women with two 0.625-mg tablets daily

(Ref. 61). The steady-state AUC data are calculated from day 7 plasma

sampling. Table 2 summarizes the relationships among oral dose, total

ketone, and total diol for three estrogens.

Table 2.--Results of Pharmacokinetic Studies

------------------------------------------------------------------------

Estrogen Estrone Equilin 8,9-

---------------------------------------------------------------DHE------

Measured dose or AUC............... ........ ........ ...............

mg per 2X 0.625mg tab.............. 0.740 0.336 0.052

Total plasma ketone (nghr/

mL)............................... 94.200 43.145 13.610

Uncon.plasma ketone (nghr/

mL)............................... 4.083 1.201 0.072

Total plasma 17diol

(nghr/mL)................. 8.565 10.623 6.624

Uncon.plasma 17diol

(nghr/mL)................. 0.659 1.060 0.331

------------------------------------------------------------------------

The pharmacokinetics of Premarin components are complex, as

revealed in these data. Estrone, equilin, 8,9-dehydroestrone

(DHE), their active 17-reduced metabolites, and other

estrogenic components of Premarin circulate in the plasma both as the

conjugated (primarily sulfate ester) and unconjugated derivatives and

with various degrees of protein binding, as discussed in the OCPB

Report. There is interconversion between the ketone and 17-

reduced forms of each estrogen and among the conjugated and

unconjugated derivatives. The degree of protein binding of each

derivative may be important to its clinical activity.

Put simply, this information shows that there is not a one-to-one

relationship between the amount of each estrogen in the tablet and the

amount of active forms (derivatives) of that estrogen in the blood.

Each of the three estrogens evaluated in this clinical trial

distributes differently into its derivatives in the body. This means

that each of the three estrogens might cause different effects simply

as a result of these distributional differences.

The actual magnitude of the contribution of each derivative of any

component estrogen to the overall estrogenicity of Premarin is not well

understood. As just stated, the pharmacokinetic data show that the

ratios of the concentrations of the different derivatives are

distributed differently for those estrogens that have been studied:

Estrone, equilin, and DHE. If there are tissue-specific effects of

derivatives, then the size of a derivative's contribution could vary

depending on the tissue tested. The available data suggest that these

tissue-specific differences exist. For example, in vitro potency data

for estrone and 17-estradiol were submitted by Wyeth-Ayerst

(Ref. 74). When potency was tested by estrogen receptor binding,

estrone was shown to be much less potent than estradiol (about 200

times less), as has been previously shown by receptor binding and

cellular assays. In contrast, when potency testing was performed in a

liver (Hep-G2) cell line using functional activation, estrone's potency

appeared to be of the same order of magnitude as estradiol's potency.

The experimenters were able to show that this increased potency of

estrone resulted from its conversion to estradiol by the cells.

Therefore, in tissues that have the capability to metabolize ketone

forms to diols (e.g., estrone to estradiol), circulating ketone forms

could make a large contribution to observed effects in that tissue.

Similarly, conversion of conjugated (sulfated) forms of circulating

estrogens to the unconjugated forms has been shown to occur in target

tissues such as breast

[[Page 42568]]

(Ref. 75). In these tissues, total estrogen concentrations (i.e.,

conjugated plus unconjugated) may be more important than in tissues

that cannot convert the conjugated forms to the active, unconjugated

forms.

One striking finding in the pharmacokinetic data is the differences

in the proportions of the 17-diol concentrations resulting

from the three estrogens (sodium estrone sulfate, sodium equilin

sulfate, and DHES), compared to the ratios of the three estrogens in

the tablet. It is known that the 17-diol derivatives of

equilin and estrone are potent estrogens. The pharmacokinetic data as a

whole show that, after dosing with Premarin, the plasma concentration

of unconjugated 17-dihydroequilin is about twice (1.6 times)

as high as the concentration of 17-estradiol, even though

there is only about half as much equilin as estrone in the tablet. The

difference in the concentration of the active metabolite may account

for the known greater clinical estrogenic potency of equilin. As

discussed above, an unexpected finding from the pharmacokinetic data in

the Missouri study (Ref. 61), the most reliable data generated to date,

was that the plasma concentration of unconjugated 17-

8,9-dehydroestradiol is about half the concentration of

unconjugated 17-estradiol, even though there is more than 10

times more estrone sulfate than DHES in Premarin. This may account for

the high oral potency of DHES that has been found in the limited

clinical studies performed with this compound (Refs. 76 and 77).

Put simply, these data show that a dose of DHES results in a much

higher blood level of the active metabolite than would result from the

same dose of estrone sulfate. This finding alone suggests, but does not

prove, that a low dose of DHES could have a much larger than expected

effect.

The above pharmacokinetic data provide a basis for beginning to

understand the complex relationship between the composition of Premarin

and its clinical effects. However, this understanding is still

incomplete. The pharmacokinetics must be understood in the context of

pharmacodynamic properties of the various components, including their

clinical effects.

c. Clinical effects of Premarin. Premarin and certain Premarin

components have been tested fairly extensively in animals, particularly

rodents. Animal data, either in vitro or in vivo, have not proven to be

quantitatively predictive of the effects found in women (Ref. 78).

Therefore, animal tests, while useful in screening compounds for

activity, cannot be used to definitively assign human clinical effects.

The most confident conclusions can be drawn from human clinical

testing. The following summarizes what is known about the contribution

of Premarin components to its overall activity from in vitro or in vivo

human testing.

i. Pharmacodynamics. The term ``pharmacodynamics'' refers to

pharmacologic or clinical responses to a given concentration of a drug

in blood or other tissue.5 For example, raising or lowering

blood pressure, causing dry mouth, or constricting the pupils are

pharmacodynamic effects of various drugs. Pharmacodynamic effects can

be beneficial, harmful, or neutral. The benefits of most drugs derive

from their desired pharmacodynamic effects, while drug side effects

often result from undesirable pharmacodynamic activity.

---------------------------------------------------------------------------

\5\ See footnote 3, supra.

---------------------------------------------------------------------------

Premarin and its components, like other estrogens, affect a wide

variety of human tissues, including pituitary, breast, uterus, bone,

liver, and endothelium (Ref. 47). Some of these actions result in the

beneficial effects of the drug, some cause side effects, and some (for

example, cardiovascular or lipoprotein effects) have not been

definitively evaluated. There are studies in the literature of effects

of estrogen on each of these tissues, especially effects on the

pituitary, uterus, and bone. This section discusses the pharmacodynamic

effects of Premarin and its components other than the relief of

menopausal symptoms and prevention of osteoporosis.

A dose-response relationship exists between estrogen treatment and

FSH suppression (Ref. 79). Some pharmacodynamic data on suppression of

FSH, including dose-response data, exist for equilin sulfate, estrone

sulfate, and Premarin (see also menopausal symptoms, below) (Refs. 5,

6, 50, and 80). In a study of suppression of urinary gonadotrophins,

equilin was found to be about twice as potent as Premarin and five

times more potent than estrone sulfate for this effect, while Premarin

was 2.5 times more potent than estrone sulfate (Ref. 6). In studies of

human serum FSH levels, Premarin has been found to be about 1.4 to 2.0

times as potent as estrone sulfate (Refs. 50 and 81). These studies are

in relative agreement.

The published data on the effects of Premarin and its components on

uterine or vaginal markers are limited. Beck and Friedrich found

equilin sulfate to be two to three times more potent than Premarin for

effects on vaginal epithelium and endometrium (Ref. 82). Varma et al.

found Premarin to be twice as potent as estrone sulfate for endometrial

changes (Ref. 81). Geola et al. evaluated the dose-response

relationship between Premarin and vaginal cytologies and concluded that

1.25 mg Premarin daily was necessary for achieving full replacement

levels for this parameter (Ref. 80). These studies are not adequate for

drawing firm conclusions about the relative contributions of equilin

and estrone to the effects of Premarin on uterine or vaginal markers.

A number of studies of Premarin or its components have evaluated

pharmacodynamic markers of bone effects (Refs. 14, 51, 79, 80, and 83).

Jones et al. estimated that Premarin was twice as potent as estrone

sulfate for reduction of the urinary calcium/creatinine ratio. This

ratio is a measure of bone resorption. Geola et al. performed a dose-

response study evaluating the effect of Premarin on the calcium/

creatinine ratio, and found that 0.3 mg Premarin was the lowest dose to

have a significant effect. Lobo et al. found that Premarin was twice as

potent as both estrone sulfate and equilin sulfate for reduction of the

urinary calcium/creatinine ratio. The Lobo finding of a significant

effect of 0.3 mg Premarin was not duplicated in a larger study by

Lindsay et al. (Ref. 14). Because of limitations in study designs and

because the pharmacodynamic markers for bone are not sufficiently

quantitative, no conclusions about comparative pharmacodynamic effects

on bone of Premarin or its components can be drawn from these results.

Data on Premarin or Premarin component effects on lipoproteins and

other plasma proteins, or other pharmacodynamic markers are quite

limited (Refs. 49, 50, 51, 53, and 84). Having information about these

effects is important for several reasons. Stimulatory effects on liver

proteins may affect drug safety. In addition, as discussed in the OCPB

Report (Ref. 71), levels of circulating unconjugated estrogens may be

affected by binding to plasma proteins, particularly sex hormone

binding globulin (SHBG). Stimulation of SHBG could alter drug

availability. Available data suggest that certain Premarin components

differ in the ability to stimulate SHBG (Ref. 50). Human

pharmacodynamic data on DHES submitted by Wyeth-Ayerst demonstrated

that 1.25 mg estrone sulfate had a much greater effect on SHBG levels

than did 0.125 mg DHES (Ref. 85); however, this result requires

confirmation.

Taken as a whole, the available pharmacologic data demonstrate that

[[Page 42569]]

estrone sulfate (as the piperazine salt), equilin sulfate, and Premarin

have different pharmacodynamic effects when potency on various tissues

is evaluated (Refs. 6, 50, 51, and 53). For example, in a single study,

Premarin was found to be 1.4 times more potent than piperazine estrone

sulfate (expressed as the sodium rather than piperazine salt) for FSH

suppression, a pituitary effect (Ref. 50). In contrast, Premarin was

3.5 times more potent than estrone sulfate for stimulation of

angiotensinogen and 3.2 times more potent for stimulation of sex

hormone binding globulin (SHBG). Presumably, this difference arises

because other components of Premarin contribute to these effects in a

manner different from estrone sulfate. It is not known if these

differential pharmacodynamic effects are completely attributable to the

presence of equilin sulfate.

In summary, the two Premarin components that have been carefully

studied, equilin sulfate and estrone sulfate, differ from each other

and from Premarin in phamacodynamic profile. It is not well understood

which of the pharamcodynamic actions are desirable and which contribute

to unwanted side effects. Adequate characterization of Premarin will

require an understanding, based on scientific data, of those Premarin

components that contribute to the pharmacodynamic effects of Premarin.

ii. Clinical effects: menopausal symptoms. A number of clinical

studies evaluating Premarin and Premarin components for the treatment

of menopausal symptoms have been performed (Refs. 79, 80, 82, and 86).

Equilin sulfate has been found to be about three times more potent than

Premarin for alleviating vasomotor symptoms (Ref. 82). The data

submitted by Wyeth-Ayerst on DHES show that DHES is more potent than

estrone sulfate for these effects, but the data are not adequate to

precisely assign a potency (Ref. 76). Without dose-response studies to

determine the potency of DHES for menopausal symptoms relative to the

potency of estrone sulfate and equilin sulfate, the contribution of

DHES to the activity of Premarin in treating menopausal symptoms cannot

be determined. Similarly, without a head-to-head comparison of the

dose-related effects of Premarin, estrone sulfate, and equilin sulfate

in the treatment of menopausal symptoms, the extent of contribution of

the two components to the overall estrogenic potency of Premarin for

this effect also cannot be accurately determined, although it is clear

that both contribute.

iii. Clinical effects: osteoporosis. (1) Use of surrogate markers.

The goal of preventive therapies for osteoporosis is the prevention of

fractures and deformity. For estrogens, FDA accepts measurement of bone

mineral density as an adequate surrogate for preventing these longer

term clinical outcomes (Ref. 87). A number of other markers for

evaluating pharmacodynamic effects on bone have been developed (Ref.

88). None of these other markers is sufficiently well understood or

quantitative to permit its use as a surrogate for osteoporosis

prevention effects. Therefore, in the absence of other validated

surrogate markers, definitive data on bone effects must come from human

trials evaluating bone mineral density, fractures, and/or deformity.

(2) Use of blood 17-estradiol levels as a surrogate

marker. Comments submitted to the docket of Wyeth-Ayerst's citizen

petition (Ref. 89), as well as statements in the scientific literature,

assert that achievement of certain levels (e.g., 39 picograms (pg)/

milliliter (mL) (Palacios et al.) or greater than 60 pg/mL (Reginster

et al.)) of serum 17-estradiol is an adequate surrogate for

preservation of bone mineral density because there is a strong

correlation between the two both in clinical trials and in untreated

perimenopausal women (Refs. 83 and 90).

The study by Palacios et al. evaluated women who had undergone

surgical menopause and who were randomized to percutaneous estradiol,

conjugated estrogens (source unspecified), or no therapy over 2 years.

Untreated women lost a mean of 9 percent of spine bone mineral density

over 2 years, whereas the estradiol treated group and the conjugated

estrogens treated group gained 4.1 percent and 5.6 percent spinal bone

mineral density respectively. Women treated with percutaneous estradiol

were reported to have a mean serum estradiol level of about 80 pg/mL

over the course of the study. The conjugated estrogens treated women

had a mean serum estradiol level of about 40 pg/mL. It is not possible

to conclude anything about a protective level of 17-estradiol

from the conjugated estrogens arm of this study since conjugated

estrogens also contain, at a minimum, equilin and possibly other

components that contribute to the effect on bone. The value of 80 pg/mL

from the percutaneous estradiol arm is not inconsistent with the data

reported by Reginster et al. who found that circulating levels of

17-estradiol between 60 and 90 pg/mL correlated well with

pharmacodynamic markers of beneficial bone effects. This correlation

suggests, but does not prove, that estrogen replacement therapies

achieving such levels of circulating estradiol may be effective in

preventing bone loss.

FDA does not currently accept 17-estradiol levels as an

adequate surrogate for osteoporosis prevention in women. Trials of bone

mineral density are required. In addition, the available data do not

indicate that the potentially protective levels of 17-

estradiol are attained after administration of Premarin.

The Palacios study found that treatment with conjugated estrogens

0.625 mg resulted in a mean estradiol level of 40 pg/mL, which is below

the 60 pg/mL minimum suggested by Reginster. However, the Librach and

Nickel study submitted to the docket, as well as the Reginster study

and other data reported in the literature, found that serum levels of

17-estradiol above 60 pg/mL are achieved in women treated with

Premarin or a Canadian generic copy of Premarin (Refs. 89 and 91). In

the Librach and Nickel study, women treated with Premarin achieved a

17-estradiol level of 85.5 pg/mL while women treated with the

Canadian product had mean serum levels of 94.9 pg/mL. These differences

appear to relate to problems with analytical methodology, possibly due

to cross-reactivity of radio-immunoassay reagents with other components

in Premarin. When serum 17-estradiol is measured by direct

chemical means, the high 17-estradiol levels are not found in

women treated daily with 0.625 mg Premarin (Refs. 60 and 61). This

latter finding is corroborated by data from a study of the effects of

esterified estrogens (Estratab, USP) on bone mineral density, which was

recently presented in abstract (Ref. 92). In this study, daily dosing

with 0.625 mg of esterified estrogens, which contains approximately

0.518 mg sodium estrone sulfate (Ref. 93) (0.625 mg Premarin contains

about 0.370 mg sodium estrone sulfate) resulted in a mean plasma

concentration of 17-estradiol of 40 pg/mL. In addition, in

this same study, daily administration of 0.3 mg esterified estrogens,

which contain about 0.248 mg sodium estrone sulfate, resulted in a mean

plasma concentration of 26 pg/mL of 17-estradiol. These

results are inconsistent with the serum level results presented by

Librach and Nickel, but generally agree with Palacios' findings and

with Wyeth-Ayerst's bioavailability data. Therefore, the available data

on serum 17-estradiol levels do not indicate that levels over

60 pg/mL are

[[Page 42570]]

attained with the dose of Premarin recommended for the prevention of

osteoporosis.

iv. Clinical effects: bone mineral density. The clinical effects of

Premarin on bone are well established. A number of clinical trials have

confirmed the effects of Premarin in preserving and increasing bone

mineral density in postmenopausal women (Refs. 13, 14, and 94).

Ettinger et al. demonstrated in a nonrandomized trial that 0.3 mg

Premarin, when administered with calcium supplementation, was adequate

to prevent bone mineral loss in the spine and hip (Ref. 95). The recent

Post-menopausal Estrogens/Progestins Intervention (PEPI) trial

demonstrated that the currently recommended 0.625 mg dose of Premarin

resulted in an increase in bone mineral density in women treated for

over 2 years, while untreated women lost bone (Ref. 96).

Estrone is approved as a single estrogen (marketed under the brand

name Ogen by Upjohn, generic name estropipate), but as a different salt

from the estrone in Premarin (the piperazine rather than the sodium

salt of estrone sulfate) for the treatment of menopausal symptoms and

the prevention of osteoporosis. The recommended dose for osteoporosis

is 0.75 mg of estropipate, which is equivalent to 0.625 mg sodium

estrone sulfate. A dose-response study has shown that a dose equivalent

to 0.300 mg estrone sulfate, combined with 1 gram daily calcium

supplementation, is not effective in preserving bone mineral density

(Ref. 97). In this study, 0.625 mg of estrone sulfate resulted in

preservation of bone mineral density compared to baseline. There was no

statistically significant difference in bone mineral density between

patients dosed with 0.625 mg and those given 1.25 mg; however, only the

1.25 mg group had bone mineral densities statistically greater than the

placebo group at 2-year followup. Based on the data from this trial,

the amount of estrone sulfate in Premarin (approximately 0.370 mg) is

too small to account for all of Premarin's known effects on bone

mineral density, so other estrogens present in the product must be

contributing to this effect.

Additional information on the effects of equilin on bone has

recently become available. On October 30, 1996, Duramed submitted to

the docket an abstract of a clinical study that had recently been

presented at a scientific meeting (Ref. 89). The study provided new

information germane to the clinical effects of Premarin on bone (Ref.

55). This study, sponsored by Solvay Pharmaceuticals, was a clinical

trial of their product, Estratab (this trial was also discussed in the

section on estradiol blood levels). Estratab is a generic esterified

estrogens product. Esterified estrogens USP contain sodium estrone

sulfate and sodium equilin sulfate in different amounts than are in

Premarin (Ref. 98) (based on presentations by Solvay, 0.300 mg of their

esterified estrogens product contains approximately 0.248 mg estrone

sulfate and 0.038 mg equilin sulfate) (Ref. 93). The study was a 2-year

placebo controlled trial testing three doses of Estratab combined with

calcium supplementation in postmenopausal women evaluating bone mineral

density and side effects. According to the abstract, all three doses

were effective at 12, 18, and 24 months in preserving bone mineral

density compared to placebo. The abstract reveals a dose response among

the three Estratab doses tested. Also significant is the fact that the

lowest dose tested, 0.3 mg Estratab, appeared to be effective in

preserving bone mineral density when given continuously in conjunction

with calcium supplementation. There are lower amounts of both estrone

sulfate and equilin sulfate in this dose of Estratab than are required

to be in the 0.625 mg tablet of generic conjugated estrogens according

to the current conjugated estrogens USP monograph. Therefore, if the

data in the abstract are correct, it could be concluded that a product

containing the amounts of estrone sulfate and equilin sulfate required

in the current monograph for conjugated estrogens USP would be

effective in preserving bone mineral density when given continuously

with supplemental calcium. Since the study by Harris et al. (Ref. 97)

showed that 0.3 mg of estrone sulfate alone is not effective in

preserving bone mineral density, then it is likely that there was a

contribution from the equilin sulfate in the Solvay product, although

firm conclusions cannot be drawn from cross-study comparisons. This

information addresses to some extent one of the questions raised in

FDA's ``Preliminary Analysis of Scientific Data on the Composition of

Conjugated Estrogens,'' (Ref. 35) that is, that the contribution of

equilin to preserving bone mineral density had not been demonstrated.

Despite this additional information, the question of what are the

active ingredients in Premarin for the indication of maintaining bone

is not completely resolved. The Solvay study demonstrated a dose

response for bone mineral density. The lowest dose, 0.3 mg, was

effective in preserving bone density. The two higher doses, 0.625 mg

and 1.25 mg, of esterified estrogen actually increased bone density

over the 2-year period. This finding is consistent with other published

data (Refs. 54 and 61). In the case of the Solvay study, it is not

known whether, at the higher doses, more women responded with bone

preservation than at lower doses, or whether women who would have

responded to 0.3 mg simply had a larger response to the higher doses.

In either case, estrogenic potency has been shown to be important to

the clinical effect on bone within this dose range. It has been

estimated that a proportion of women taking the recommended dose of

Premarin continue to lose bone mineral, even though mean values are

sustained or improved (Ref. 99).

The finding that sodium equilin sulfate and sodium estrone sulfate,

at the doses present in Estratab, preserve bone mineral density

provides support for the proposition that equilin contributes to the

bone preservation effects of Premarin. However, as discussed at the

beginning of this memorandum, the requirement for approval of an ANDA

is not that generic drugs have effects similar to the reference listed

drug but, rather, that they have the same active ingredients. Only if

the active ingredients are the same can generic copies be relied upon

to have the same estrogenic potency and, therefore, the same effects on

bone.

Limited data on the pharmacodynamic effects of DHES on bone have

been submitted by Wyeth-Ayerst (Refs. 76 and 77). These data show that

DHES has a pharmacodynamic effect on bone markers, but the data do not

shed light on whether the DHES component of Premarin has a meaningful

clinical effect on bone.

v. Safety. There are safety concerns about all estrogen

preparations currently approved for long-term administration for the

prevention of osteoporosis. Long-term estrogen administration is

associated with an increased incidence of endometrial cancer in women

who have not undergone hysterectomy, and there is an ongoing

controversy about the relationship of long-term estrogen replacement

therapy to breast cancer.

No head-to-head studies have compared the long-term safety of

various estrogen preparations when used chronically for the prevention

of osteoporosis. The available epidemiologic evidence, summarized at

the July 27 and 28, 1995, Advisory Committee meeting, does not

definitively establish safety differences among various estrogens (Ref.

100). Thus, it is not known to what extent, if

[[Page 42571]]

any, differences in the types of estrogens used may affect safety.

There are no comparative safety trials of Premarin components

available. There are few pharmacodynamic markers available with which

to assess safety for effects such as cancer. Therefore, sufficient

clinical data do not exist to fully characterize the contributions

(either positive or negative) of various Premarin components to its

clinical safety.

vi. Other pharmacologic effects. There is currently intense

interest in the role of estrogen replacement therapy (ERT) in the

prevention of cardiovascular disease and possibly other age-related

disorders in women (Ref. 101). No estrogen product is currently

approved by FDA for such indications. If Premarin were to be found

effective for prevention of cardiovascular disease, elucidating the

effects of Premarin and its components on relevant pharmacodynamic

parameters would be important in fully characterizing the product.

There are clinical data suggesting that equine estrogens may have

differential effects on parameters such as lipoprotein levels and lipid

peroxidation (Refs. 51 and 84); however, these data are as yet very

incomplete.

d. Inclusion of 8,9-dehydroestrone sulfate (DHES). Many of

the issues raised by Wyeth-Ayerst in its citizen petition submitted in

November 1994, and addressed in numerous submissions to the docket,

pertain to the need to include DHES in generic copies of Premarin. The

scientific issues related to this compound are addressed below insofar

as they relate to the approvability of generic copies of Premarin, such

as Duramed's and Barr's synthetic conjugated estrogens products.

As discussed previously at the beginning of this section (section

III.B.2), DHES is a conjugated estrogens component that comprises about

4.4 percent of the ``label claim'' of Premarin. It has been recognized

as a constituent of Premarin for two decades (Ref. 57). However, little

scientific data have been available on its activity, and it has been

treated as an impurity. Information submitted by Wyeth-Ayerst on the

pharmacokinetics of DHES in Premarin reveal that its metabolite,

17-8,9-dehydroestradiol, is present in surprisingly

large concentrations in the plasma, considering the composition of the

tablet (Refs. 59 and 60). FDA analyses support this finding (Ref. 71).

The 17-8,9-dehydroestradiol concentration is

important because the diol form of estrogen is usually the most active

in the human body. After taking Premarin, the concentration (or AUC) of

unconjugated 17-8,9-dehydroestradiol in the plasma is

between 50 percent and 125 percent (depending on what study results are

used) of the concentration of unconjugated 17-estradiol and is

one-third the concentration of unconjugated 17-dihydroequilin.

The fact that a component is present at high concentrations in the

plasma does not necessarily mean that it is clinically important. The

significance of the finding that 17-8,9-

dehydroestrodiol is present in high concentrations depends on the

potency of 17-8,9-dehydroestradiol compared to the

potency of the other circulating estrogens. If it is assumed that the

potency of the 17-diol metabolites derived from estrone

sulfate, equilin sulfate, and DHES have equal potency, then the

contribution of DHES to the overall estrogenic activity of the

17-diol metabolites of the three estrogens would be 16 percent

(based on unconjugated diol AUC's) to 26 percent (based on total diol

AUC's) (Ref. 61). However, there are several ways to evaluate relative

potency of estrogens. One method, testing in animal species, is useful

for determining estrogenicity, but has not proven to be quantitatively

predictive for humans (the original rat potency test for conjugated

estrogens is a good example). This could be due to interspecies

differences in metabolism, some of which have been confirmed (Ref.

102).

If animal testing is not adequately quantitative, in vitro studies

using human cells or receptors may be performed, or human clinical

tests may be carried out. Scientific data of both types assessing the

relative potency of DHES have been submitted to the docket. Wyeth-

Ayerst provided data on human estrogen receptor binding as well as

functional activation data in HEP-2 cells (Ref. 103). In addition,

Duramed provided data on functional activation of Ishikawa cells, a

human uterine cell line (Ref. 104). The results of these studies are

summarized in the OCPB Report of October 25, 1996 (Ref. 71), Addendum 1

to that report dated February 12, 1997 (Ref. 72), and Addendum 2 to

that report dated March 31, 1997 (Ref. 73). These OCPB Reports attempt

to quantify the clinical estrogenic contribution to Premarin from

equilin, estrone, DHE, and 17-dihydroequilin based on the potencies

derived from the various in vitro assays in combination with the

pharmacokinetic data.

The OCPB Report estimates that, based on the in vitro potencies and

the known pharmacokinetics, DHE and its metabolite contribute

approximately 2.8 to 6.5 percent of the overall estrogenic potency of

Premarin, depending on the assumptions used (Ref. 105).

Just as with the animal data, it is important to try to assess how

reliably the in vitro data predict the actual clinical outcomes. A

limitation of cellular assays is that only one tissue type is

evaluated. The results of the OCPB analysis shows that widely differing

estimates are arrived at depending on the system used (Ref. 106). This

may be due to artifacts of the system (i.e., metabolism of estrone to

estradiol, etc., in the Hep-G2 cells), true tissue differences, or

other reasons. The best way to evaluate the in vitro potency

assignments is to compare their results with known clinical outcomes.

In this case, certain comparisons are possible because both estrone

sulfate and equilin sulfate have been tested in women as single

ingredients (Refs. 6 and 51). A number of clinical studies have shown

that, for both FSH suppression and treatment of menopausal symptoms,

equilin sulfate is roughly five times more potent than estrone sulfate

when administered as a single ingredient. Comparison of this known

clinical fact to the potency estimates in Tables 3 and 4 of OCPB

Addendum 2 reveals that the Ishikawa cell potencies do not correctly

predict the oral potency of equilin relative to estrone (Ref. 73). The

Ishikawa cell data predict that oral equilin sulfate would be

equipotent to or less potent than estrone sulfate. Of the other in

vitro estimates, the estrogen receptor binding assay best predicts the

known differences between equilin and estrone, predicting equilin

sulfate to be between two to four times more potent than estrone

sulfate depending on the assumptions used. Because of these widely

differing estimates, it must be concluded that in vitro assays, even in

human systems, cannot currently be relied upon to provide precise

predictions of relative clinical potencies.

The other information available on the relative potency of DHES

comes from human studies. Wyeth-Ayerst submitted the results of two

human studies to the docket (Refs. 76 and 77). These studies were

small, unblinded, uncontrolled trials, and would not be of the type

relied upon for determining safety or efficacy of a drug. In addition,

they did not use a dosage form equivalent to that of Premarin, and thus

their results cannot be directly extrapolated to Premarin. However,

they are quite similar to the types of studies that were originally

used to evaluate the role of estrone sulfate and equilin sulfate in

Premarin and can be used to assess certain comparative pharmacodynamic

parameters. In these

[[Page 42572]]

trials, 0.125 mg of DHES was administered daily to postmenopausal

women. This dose of DHES is about four times the amount in a 0.625 mg

tablet of Premarin. In both studies, this dose of DHES caused

approximately 15 to 26 percent suppression of FSH after 2 weeks of

dosing. This is in the range of suppression resulting from 0.625 mg of

estrone sulfate reported in the literature (Ref. 50). The study

performed in Brazil included a comparison group given 1.25 mg estrone

sulfate. This group achieved approximately a 40 percent reduction in

FSH levels at 2 weeks. This effect is somewhat greater than has been

previously reported (Refs. 50 and 81).

Based on these human data, the oral potency of DHES (for pituitary

pharmacodynamic parameters) is (very roughly) five to six times that of

estrone sulfate, or very similar to that of equilin sulfate and is

about what would be predicted on pharmacokinetic grounds if the estrone

and DHE derived diols were roughly equipotent. DHE, like equilin, is a

B ring unsaturated estrogen. If DHES has the same oral potency as

equilin and if the contributions of estrone sulfate, equilin sulfate,

and DHES plus the small amount of 17-8,9-

dehydroestradiol sulfate were to be considered, then DHES and its

metabolite would contribute about 9 percent of the estrogenic potency

from these three components, at least for pituitary parameters.

It can be seen from the above analysis that the high end of the

estimate of the contribution of DHES to the estrogenic potency of

Premarin from the in vitro assays is similar to the estimate derived

from clinical studies, i.e., about 9 percent, and both of the estimates

are lower than the 16 percent to 26 percent estimate based on an

assumption that each 17-diol metabolite is equally potent.

Unfortunately, all of the estimates have problems and uncertainties. A

precise estimate of the potency of DHES relative to estrone sulfate is

not available. In addition, none of the data provide insight into the

contribution of these components to estrogenic potency with respect to

bone. As discussed above, preliminary pharmacodynamic data indicate

that DHES has an effect on bone markers. The available data demonstrate

that DHES is a potent estrogen and may make a clinically meaningful

contribution to the therapeutic effects of Premarin.

C. Conclusions

CDER proposes to refuse to approve Duramed's ANDA 40-115 and Barr's

ANDA 40-154 primarily on the grounds that Duramed and Barr have failed

to provide sufficient information to show that the active ingredients

of their respective synthetic conjugated estrogens products are the

same as the active ingredients of the reference listed drug product,

Premarin. For a generic drug product with Premarin as the reference

listed drug to be approved without approval of a petition under

Sec. 314.93 (21 CFR 314.93), the generic drug must have the same active

ingredients as Premarin. This requirement, paired with a showing of

bioequivalence of the generic drug to the reference listed drug, is

meant to ensure that the data developed by the innovator company to

demonstrate the safety and effectiveness of the reference listed drug

will support approval of the generic drug. Independent demonstration of

safety and effectiveness is not required for approval of generic drugs.

Approval of generic copies of Premarin manufactured from combined

synthesized components requires data sufficient to demonstrate that

such copies contain the same active ingredients as Premarin.

CDER has determined that the reference listed drug Premarin is not

adequately characterized at this time. In particular, the estrogenic

potency of the product is not clearly defined relative to the

estrogenic potency of its constituents. In addition, the contribution

of the two most abundant estrogens, sodium equilin sulfate and sodium

estrone sulfate, to the overall estrogenic potency is not well

understood. Furthermore, the quantitative composition of Premarin with

respect to potentially pharmacologically active components has not been

defined. Without this information it is not possible to define the

active ingredients of Premarin.

Investigations designed to produce the scientific data needed to

determine the active ingredients are feasible. Such information would

allow a determination of which components of Premarin make a clinically

meaningful contribution to its overall effects. It is both feasible and

desirable for the constituent active ingredients in Premarin to be

characterized to this extent.

With regard to sodium 8,9-dehydroestrone sulfate (DHES),

the available scientific evidence indicates that DHES is an active

estrogen that contributes to the estrogenic potency of Premarin. The

clinical significance of this contribution has not been determined.

DHES must be included in generic copies of Premarin unless scientific

data are presented that demonstrate that the estrogenic activity of

DHES is not clinically meaningful. Duramed and Barr have failed to

provide sufficient information in their ANDA's to show that their

conjugated estrogens products contain this same ingredient, or that the

estrogenic activity of DHES is not clinically meaningful.

In addition to failing to provide sufficient information to show

that the proposed generic drugs contain the same active ingredients as

the reference listed drug, ANDA 40-115 and ANDA 40-154 also fail to

provide sufficient information to demonstrate that such proposed

generic drug products are bioequivalent to the reference listed drug.

Under section 505(j)(3)(F) of the act and Sec. 314.127(a)(6), FDA

must refuse to approve an ANDA for a proposed generic drug, unless

sufficient information has been submitted to show that such drug is

bioquivalent to the reference listed drug.6 Bioequivalence

depends on the rate and extent to which the active ingredient or active

moiety becomes available at the site of action. See section

505(j)(7)(B) of the act and Sec. 320.1(e). If a drug has not been

established to contain the same active ingredients or active moieties,

bioequivalence cannot be established. CDER finds that ANDA 40-115 and

ANDA 40-154 do not present sufficient information to show that the

proposed generic drugs contain the same active ingredients or the same

active moieties as the reference listed drug. Therefore, these ANDA's

cannot be approved by FDA under section 505(j)(3)(F) of the act and

Sec. 314.127(a)(6) because they fail to present sufficient information

to show that the proposed generic drugs are bioequivalent to the

reference listed drug.

---------------------------------------------------------------------------

\6\ One exception to this general rule that is not applicable

here relates to a drug for which a petition under section

505(j)(2)(C) of the act and Sec. 314.93 has been approved. See

Sec. 314.127(a)(6)(ii).

---------------------------------------------------------------------------

Finally, in the event that each of the foregoing deficiencies is

resolved, additional information may be required to address unresolved

labeling, chemistry, bioequivalence, or manufacturing issues.

IV. References

The following references have been placed on display in the Dockets

Management Branch (address above) and may be seen by interested persons

between 9 a.m. and 4 p.m., Monday through Friday. Additional documents

related to this notice appear in Dockets 94P-0429 and 94P-0430, and are

incorporated by reference.

1. United States Pharmacopeia 18, pp. 242-246, 1970.

[[Page 42573]]

2. Minutes of the meeting of the Committee on Conjugated

Estrogens of the Pharmaceutical Contact Section, Washington, DC,

October 23, 1962.

3. Minutes of the meeting of the Committee on Conjugated

Estrogens of the Quality Control Section, Washington, DC, April 16,

1963.

4. Summary of Proceedings of the USP Conference on Conjugated

Estrogens, February 27, 1968.

5. Howard, R. P., E. C. Keaty, and E. C. Reifenstein,

``Comparative Effects of Various Estrogens on Urinary Gonadotropins

(FSH) in Oophorectomized Women,'' [Abstract], Journal of Clinical

Endocrinology and Metabolism, 16:966, 1956.

6. Howard, R. P., and E. C. Keaty, ``Evaluation of Equilin 3-

monosulfate and Other Estrogens,'' Archives of Internal Medicine,

128:229-234, August 1971.

7. FDA, ``Certain Estrogen-Containing Drugs for Oral or

Parenteral Use,'' Federal Register, Vol. 37, No. 143, pp. 14826-

14828, July 25, 1972.

8. Minutes of the meeting on proposed USP monograph for

conjugated estrogens, p. 4, November 4, 1982.

9. Id. at pp. 1-4.

10. FDA, ``Therapeutically Equivalent Drugs,'' Federal Register,

Vol. 44, No. 9, pp. 2932-2953, January 12, 1979. Announced that FDA

intended to make available a list of approved drug products with

therapeutic evaluations of products available from more than one

manufacturer. Originally known as Approved Prescription Drug

Products with Therapeutic Equivalence Evaluations, it is now called

Approved Drug Products with Therapeutic Equivalence Evaluations (the

Orange Book).

11. 1980 Orange Book listing for conjugated estrogens, pp. 51-

52.

12. FDA, ``Oral Estrogens for Postmenopausal Osteoporosis; Drug

Efficacy Study Implementation; Reevaluation,'' Federal Register,

Vol. 51, No. 70, pp. 12568-12570, April 11, 1986.

13. Genant, H. K., C. E. Cann, B. Ettinger, and G. S. Gordan,

``Quantitative Computed Tomography of Vertebral Spongiosa: A

Sensitive Method for Detecting Early Bone Loss After Oophorectomy,''

Annals of Internal Medicine, 97:699-705, 1982.

14. Lindsay, R., D. M. Hart, and D. M. Clark, ``The Minimum

Effective Dose of Estrogen for Prevention of Postmenopausal Bone

Loss,'' Obstetrics and Gynecology, 63:759-763, 1984.

15. FDA, ``Abbreviated New Drug Applications for Conjugated

Estrogens; Proposal to Withdraw Approval; Opportunity for a

Hearing,'' Federal Register, Vol. 55, No. 30, pp. 5074, 5076-5078,

February 13, 1990.

16. Id. at p. 5076.

17. FDA, Center for Drug Evaluation and Research, Division of

Bioequivalence, Guidance for ``In-Vivo Bioequivalence Study for

Conjugated Estrogens Tablets,'' December 17, 1986.

18 Transcript, Vol. II, and Summary Minutes of the meeting of

FDA's Fertility and Maternal Health Drugs Advisory Committee,

January 5-6, 1989.

19. Id. at pp. 177-193.

20. Transcript and Summary Minutes of the meeting of the Ad Hoc

Subcommittee of FDA's Fertility and Maternal Health Drugs Advisory

Committee, Vols. I and II, May 3-4, 1990.

21. Id., Vol. II, pp. 117-135.

22. FDA, ``Abbreviated New Drug Applications for Conjugated

Estrogens; Proposal to Withdraw Approval; Opportunity for a

Hearing,'' Federal Register, Vol. 55, No. 30, pp. 5074, 5076-5078,

February 13, 1990.

23. FDA, ``Conjugated Estrogens Tablets; Withdrawal of Approval

of 28 Abbreviated New Drug Applications,'' Federal Register, Vol.

56, No. 57, p. 12376, March 25, 1991.

24. FDA, ``Zenith Laboratories; Conjugated Estrogens Tablets;

Withdrawal of Approval of Four Abbreviated New Drug Applications,''

Federal Register, Vol. 56, No. 87, p. 20621, May 6, 1991.

25. Transcript of the meeting of FDA's Generic Drugs Advisory

Committee, Vols. I and II, February 25-26, 1991.

26. Id., Vol. I, pp. 46-68.

27. Adams, W. P., presentation slide from the meeting of the

FDA's Generic Drugs Advisory Committee, February 25, 1991.

28. Transcript of the meeting of FDA's Generic Drugs Advisory

Committee, Vol. I, pp. 68-91, February 25-26, 1991.

29. Transcript of the meeting of FDA's Generic Drugs Advisory

Committee, Vol. II, pp. 16-26, February 25-26, 1991.

30. USP, Pharmacopeial Forum, Vol. 17, No. 6, pp. 2-3, December

1991.

31. Wyeth-Ayerst submission to the docket 94P-0429 (CP 1),

November 30, 1994.

32. Wyeth-Ayerst submission to the docket 94P-0430 (PSA 1),

November 30, 1994.

33. Transcript and Summary Minutes of the meeting of FDA's

Fertility and Maternal Health Drugs Advisory Committee, Vols. I and

II, July 27-28, 1995.

34. Id., Summary Minutes, p. 5, and Vol. II, pp. 296-297.

35. FDA submission to the docket 94P-0429 (REF 1), November 4,

1996. FDA's ``Preliminary Analysis of Scientific Data on the

Composition of Conjugated Estrogens,'' November 1, 1996.

36. FDA, Ad Hoc Conjugated Estrogens Working Group, ``Ad Hoc

Conjugated Estrogens Working Group Final Report,'' [with

attachments], May 1, 1997.

37. Memorandum from the Director, Office of Drug Evaluation II

to the Director, Center for Drug Evaluation and Research, ``Generic

Drug Versions of Conjugated Estrogens,'' April 22, 1997.

38. Memorandum from the Associate Director for Medical Policy to

the Director, Center for Drug Evaluation and Research, ``Conjugated

Estrogens; Requirements for a Generic Product,'' [with attachments],

May 4, 1997.

39. Memorandum from the Director, Office of Pharmaceutical

Science to the Director, Center for Drug Evaluation and Research,

``Recommendation on the Composition of Conjugated Estrogens Tablets,

USP,'' [with attachments; redacted], May 3, 1997.

40. FDA, ``Abbreviated New Drug Application Regulations;

Proposed Rule,'' Federal Register, Vol. 54, No. 130, pp. 28872

(28880, 28881), July 10, 1989. States that to be ``the same,''

active ingredients must be ``identical.''

41. United States Pharmacopeia 18, pp. 242-245, 1970.

42. FDA, ``Conjugated Estrogens Background Information for the

Fertility and Maternal Health Drugs Advisory Committee Meeting,''

pp. 11-13, July 27-28, 1995.

43. United States Pharmacopeia 23, ``Conjugated Estrogens

Monograph,'' pp. 627-629, 1995.

44. Wyeth-Ayerst submission to the docket 94P-0429 (SUP 4),

``Contributions of 8,9-dehydroestrone (8,9 DHES)

to the Biologic Activities of Conjugated Estrogens,'' p. 13,

September 25, 1995.

45. Yang, N.N., M. Venugopalan, S. Hardikar, and A. Glasebrook,

``Identification of an Estrogen Response Element Activated by

Metabolites of 17B-estrodiol and Raloxifene,'' Science, 273:1222-

1225, August 30, 1996.

46. Kuiper, G. G. J. M., E. Enmark, M. Pelto-Huikko, et al.,

``Cloning of a Novel Estrogen Receptor Expressed in Rat Prostate and

Ovary,'' Proceedings of the National Academy of Sciences of the

United States of America, 93:5925-5930, June 1996.

47. Barnes, R.B., and R. A. Lobo, ``Pharmacology of Estrogens,''

in Menopause: Physiology and Pharmacology, edited by D. R. Mishell,

pp. 301-315, Chicago: Year Book Medical Publishers, 1987.

48. Von Angerer, E., ``The Estrogen Receptor as a Target for

Rational Drug Design,'' Molecular Biology Intelligence Unit, pp. 5-

17, Austin: RG Landes Co., August 1995.

49. Koh, K. K., R. Mincemoyer, M. N. Bui, et al., ``Effects of

Hormone-Replacement Therapy on Fibrinolysis in Postmenopausal

Women,'' New England Journal of Medicine, 336:683-690, March 1997.

50. Mashchak, C. A., R. A. Lobo, R. Dozono-Takano, et al.,

``Comparison of Pharmacodynamic Properties of Various Estrogen

Formulations,'' American Journal of Obstetrics and Gynecology,

144:511-518, November 1992.

51. Lobo, R. A., H. N. Nguyen, P. Eggena, and P. F. Brenner,

``Biologic Effects of Equilin Sulfate in Postmenopausal Women,''

Fertility and Sterility, 49:234-238, February 1988.

52. Lyman, G. W., and R. N. Johnson, ``Assay for Conjugated

Estrogens in Tablets Using Fused-Silica Capillary Gas

Chromatography,'' Journal of Chromatography, 234:234-239, 1982.

53. Helgason, S., M-G. Damber, B. von Schoultz, and T.

Stigbrand, ``Estrogenic Potency of Oral Replacement Therapy

Estimated by the Induction of Pregnancy Zone Protein,'' Acta

Obstetrica et Gynecologica Scandinavica, 61:75-79, 1982.

54. Ettinger, B., H. K. Genant, P. Steiger, and P. Madvig,

``Low-dosage Micronized 17-estradiol Prevents Bone Loss in

Postmenopausal Women,'' American Journal of Obstetrics and

Gynecology, 166:479-488, February 1992.

55. Genant, H., J. Lucas, S. Weiss, et al., ``A Clinical Study

of 0.3, 0.625 and 1.25 mg Esterified Estrogens ([email protected]) for the

Prevention of Postmenopausal Osteoporosis,'' [Abstract PTu 577],

Osteoporosis International, 6 (Suppl. 1):S228, 1996.

56. Roman, R., C. H. Yates, J. F. Millar, and W. J. A. Vanden

Heuvel, ``Identification of Estrogens Isolated From Pregnant Mares''

[[Page 42574]]

Urine,'' Canadian Journal of Pharmaceutical Sciences, 10:8-11, 1974.

57. Johnson, R., R. Masserano, R. Haring, et al., ``Quantitative

GLC Determination of Conjugated Estrogens in Raw Materials and

Finished Dosage Forms,'' Journal of Pharmaceutical Sciences,

64:1007-1011, June 1975.

58. Wyeth-Ayerst submission to the docket 94P-0429 (C 96), March

26, 1997.

59. Wyeth-Ayerst submission to the docket 94P-0429, (SUP 10),

May 5, 1997, Doc. 1, Vol. 2, Protocol 713-X-108-US, Wyeth-Ayerst

GMR-23669, February 16, 1994, Table 46, p. 197; Table 52, p. 214;

Table 57, p. 230. Wyeth-Ayerst submission to the docket 94P-0429,

(SUP 9), October 29, 1996, Doc. 1, Vol. 5, article (Troy, S. M., D.

R. Hicks, V. D. Parker, et al., ``Differences in Pharmacokinetics

and Comparative Bioavailability Between Premarin and

[email protected] in Healthy Postmenopausal Women,'' Current Therapeutic

Research, 55:359-372, 1994); Doc. 32, GMR 21811, Table 52.

60. Wyeth-Ayerst submission to the docket 94P-0429 (Sup 4), Vol.

4, Tab 27, ``Pharmacokinetic Profile of Unconjugated and Total

(Unconjugated Plus Conjugated) 17-8,9-

dehydroestrone in Healthy Postmenopausal Women Receiving 2 x 0.625

mg Premarin and 2 x 0.625 mg Estratab,'' Wyeth-Ayerst draft addendum

to GMR-23669 for Protocol 713-X-108-US(17-8,9-

dehydroestrone pharmacokinetic data), September 20, 1995.

61. Wyeth-Ayerst submission to the docket 94P-0429 (SUP 10), May

5, 1997, Doc. 33, ``A Steady-State Bioavailability Study of

Premarin (2 x 0.625 mg) in Healthy Postmenopausal

Women--Final Report (Protocol Number 96-090MA),'' GTR 29548,

February 24, 1997, (Missouri Study).

62. FDA, Center for Drug Evaluation and Research, Division of

Drug Analysis, ``Preliminary Assay Results from FDA's Division of

Drug Analysis,'' June 1995. Referenced in FDA submission to the

docket 94P-0429 (REF 1), November 4, 1996.

63. Wyeth-Ayerst submission to the docket 94P-0429 (SUP 4),

``Contributions of 8,9-dehydroestrone (8,9 DHES)

to the Biologic Activities of Conjugated Estrogens,'' p. 14,

September 25, 1995.

64. Roos, R.W., ``Determination of Conjugated and Esterified

Estrogens in Pharmaceutical Tablet Dosage Forms by High-Pressure,

Normal-Phase Partition Chromatography,'' Journal of Chromatographic

Science, 14:505-512, November 1976.

65. Roos, R.W., and C.A. Lau-Cain, ``Liquid Chromatographic

Analysis of Conjugated and Esterified Estrogens in Tablets,''

Journal of Pharmaceutical Sciences, 74:201-204, February 1985.

66. Roos, R.W., ``High-pressure Liquid Chromatographic Analysis

of Estrogens in Pharmaceuticals by Measurement of Their Dansyl

derivatives,'' Journal of Pharmaceutical Sciences, 67:1735-1739,

December 1978.

67. Pillai, G.K., and K.M. McErlane, ``Quantitative

Determination of Conjugated Estrogens in Formulations by Capillary

GLC,'' Journal of Pharmaceutical Sciences, 70:1072-1075, September

1981.

68. The international community has recognized the need to

characterize impurities present in a new drug substance at or above

an apparent level of 0.1%. Guideline for Industry, Impurities in New

Drug Substances, International Conference on Harmonisation, Q3A,

January 1996. Given this international recognition of the

feasability of so characterizing new drug substances, it should be

possible to characterize conjugated estrogens at least to this

degree.

69. Duramed submission to the docket 94P-0429 (RC 5), p. 5,

August 22, 1996.

70. Wyeth-Ayerst submission to the docket 94P-0429 (C 96), p.

2., March 26, 1997.

71. FDA, Center for Drug Evaluation and Research, Office of

Clinical Pharmacology and Biopharmaceutics, Division of

Pharmaceutical Evaluation II, ``A Pharmacokinetic Analysis of

Conjugated Estrogens Including 8,9-Dehydroestrone and

17-8,9-Dehydroestradiol,'' October 25, 1996 (OCPB

Report).

72. Id., Addendum 1, February 12, 1997. See also Ref. 36,

Attachment B-2.

73. Id., Addendum 2, March 31, 1997. See also Ref. 36,

Attachment B-3.

74. Wyeth-Ayerst submission to the docket 94P-0429 (Sup 4), GTR-

26521, pp. 32-34, September 25, 1995.

75. Barnes, R.B., and R.A. Lobo, ``Pharmacology of Estrogens,''

in Menopause: Physiology and Pharmacology, edited by D.R. Mishell,

p. 303, Chicago: Year Book Medical Publishers, 1987.

76. Wyeth-Ayerst submission to the docket 94P-0429 (SUP 10), May

5, 1997, ``A Pilot Study on the Clinical Effects of 8,9

Dehydroestrone Sulfate Alone or in Combination with Estrone Sulfate,

Protocol CF-DHE-001 BR,'' GMR-27679, Final Study Report, November

22, 1996 (Brazilian Study).

77. Wyeth-Ayerst submission to the docket 94P-0429 (SUP 10), May

5, 1997, ``Pilot Study on the Clinical Effects of 8,9-

Dehydroestrone Sulfate,'' Summary report, (undated) (Canadian

study).

78. Stern, M.D., ``Pharmacology of Conjugated Oestrogens,''

Maturitas, 4:333-339, Elsevier Biomedical Press, 1982.

79. Jones, M.M., B. Pearlman, D.H. Marshall, et al., ``Dose-

Dependent Response of FSH, Flushes and Urinary Calcium to

Oestrogen,'' Maturitas, 4:285-290, Elsevier Biomedical Press, 1982.

80. Geola, F.L., A.M. Frumar, I.V. Tataryn, et al., ``Biological

Effects of Various Doses of Conjugated Equine Estrogens in

Postmenopausal Women,'' Journal of Clinical Endocrinology and

Metabolism, 51:620-625, 1980.

81. Varma, T.R., D. Everard, and D. Hole, ``Effect of Natural

Estrogen on the Serum Level of Follicle-Stimulating Hormone (FSH),

Estradiol and Estrone in Post-Menopausal Women and Its Effect on

Endometrium,'' Acta Obstetrica et Gynecologica Scandinavica, 64:105-

109, 1985.

82. Beck, V.A., and F.W. Friedrich, ``Equilinsulfat zur

Substitution Beim Menopause-syndrom (Equilin Sulfate in the

Treatment of the Menopausal Syndrome),'' Wiener Klinische

Wochenschrift, 87:59-62, 1975.

83. Palacios, S., C. Menendez, A.R. Jurado, and J.C. Vargas,

``Effects of Percutaneous Oestradiol Versus Oral Oestrogens on Bone

Density,'' Maturitas, 20:209-213, 1995.

84. Tang, M., W. Abplanalp, S. Ayres, and M.T.R. Subbiah,

``Superior and Distinct Antioxidant Effects of Selected Estrogen

Metabolites on Lipid Peroxidation,'' Metabolism, 45:411-414, April

1996.

85. Wyeth-Ayerst submission to the docket 94P-0429 (SUP 10), May

5, 1997, ``A Pilot Study on the Clinical Effects of 8,9

Dehydroestrone Sulfate Alone or in Combination with Estrone Sulfate,

Protocol CF-DHE-001 BR,'' GMR-27679, Final Study Report, November

22, 1996 (Brazilian Study), GMR-27679, p. 8.

86. Bradbury, J. T., and R. C. Long, ``Equilin, an Orally Active

Estrogen in Women,'' University of Louisville, Louisville, KY,

American Journal of Physiology, 163:700, 1950.

87. FDA, Center for Drug Evaluation and Research, Division of

Metabolism and Endocrine Drug Products, ``Guideline for Preclinical

and Clinical Evaluation of Agents Used in the Prevention or

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88. Calvo, M. S., D. R. Eyre, and C. M. Gundberg, ``Molecular

Basis and Clinical Application of Biological Markers of Bone

Turnover,'' Endocrine Reviews, 17:333-367, August 1996.

89. Duramed submission to the docket 94P-0429 (C 38), October

30, 1996.

90. Reginster, J. Y., N. Sarlet, R. Deroisy, et al., ``Minimal

Levels of Serum Estradiol Prevent Postmenopausal Bone Loss,''

Calcified Tissue International, 51:340-343, 1992.

91. Librach, S., and A. K. Nickel, ``Effect of C.E.S.

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92. Brennan, J. J., J. C. Nolan, J. Hui, et al., ``Plasma

Concentrations of Estrogens Are Correlated With Bone Mineral Density

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Pharmacology and Therapeutics, Vol. 61, No. 2, p. 168, February

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Pharmacology and Therapeutics, San Diego, CA, March 6, 1997.

93. Thomas, G., Solvay Pharmaceuticals, Transcript and slides

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Esterified Estrogens Tablets, USP, Rockville, MD, pp. 62-76,

September 29, 1992.

94. Stevenson, J. C., M. P. Cust, K. F. Gangar, et al.,

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to the Biologic Activities of Conjugated Estrogens,'' GTR-26521, pp.

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V. Notice of Opportunity for a Hearing

The Director of CDER (the Director) has evaluated the information

discussed above and, on the grounds stated, is proposing to refuse to

approve ANDA 40-115 and ANDA 40-154.

Therefore, notice is given to Duramed and Barr and to all other

interested persons that under section 505 (j)(3)(C)(ii), (j)(3)(F), and

(j)(3)(J) of the act and Sec. 314.127 (a)(3)(ii), (a)(6), and (a)(12),

the Director proposes to refuse to approve ANDA 40-115 and ANDA 40-154.

In accordance with section 505(j)(4)(C) of the act and

Sec. 314.200(a), the applicants are hereby given notice of an

opportunity for a hearing to show that approval of ANDA 40-115 and ANDA

40-154 should not be refused.

An applicant who decides to seek a hearing shall file: (1) On or

before September 8, 1997: a written notice of appearance and request

for hearing, and (2) on or before October 6, 1997, the data,

information, and analyses relied on to demonstrate that there is a

genuine issue of material fact to justify a hearing, as specified in

Sec. 314.200(c). Any other interested person may also submit comments

on this notice. The procedures and requirements governing this notice

of opportunity for a hearing, a notice of appearance and request for a

hearing, information and analyses to justify a hearing, other comments,

and a grant or denial of a hearing are contained in Sec. 314.200 and in

21 CFR part 12.

The failure of the applicant to file a timely written notice of

appearance and request for a hearing, as required by Sec. 314.200,

constitutes an election by that person not to use the opportunity for a

hearing concerning the proposed action, and a waiver of any contentions

concerning the legal status of the referenced drug products.

A request for a hearing may not rest upon mere allegations or

denials, but must present specific facts showing that there is a

genuine and substantial issue of fact that requires a hearing. If it

conclusively appears from the face of the data, information, and

factual analyses in the request for a hearing that there is no genuine

and substantial issue of fact that precludes the refusal to approve the

application, or when a request for a hearing is not made in the

required format or with the required analyses, the Commissioner of Food

and Drugs will enter summary judgment against the person who requests

the hearing, making findings and conclusions, and denying a hearing.

All submissions pursuant to this notice of opportunity for a

hearing are to be filed in four copies. Except for data and information

prohibited from public disclosure under 21 U.S.C. 331(j) or 18 U.S.C.

1905, the submissions may be seen in the Dockets Management Branch

(address above) between 9 a.m. and 4 p.m., Monday through Friday.

This notice is issued under the Federal Food, Drug, and Cosmetic

Act (section 505) and under authority delegated to the Director of the

Center for Drug Evaluation and Research (21 CFR 5.82).

Dated: July 29, 1997.

Murray M. Lumpkin,

Director, Center for Drug Evaluation and Research.

[FR Doc. 97-20792 Filed 8-6-97; 8:45 am]

BILLING CODE 4160-01-P