Defining Active Ingredient: The U.S. Food and Drug Administration’s Legal Interpretation of Regulatory Exclusivities

Defining Active Ingredient: The U.S.

Food and Drug Administration’s Legal

Interpretation of Regulatory Exclusivities

Updated August 8, 2023

Congressional Research Service

https://crsreports.congress.gov

R46110

SUMMARY

Defining Active Ingredient: The U.S. Food and

Drug Administration’s Legal Interpretation

of Regulatory Exclusivities

R46110

August 8, 2023

Erin H. Ward

Legislative Attorney

Whether many provisions of the Federal Food, Drug, and Cosmetic Act (FD&C Act) apply to a

particular drug product turns in part on the novelty of the “active ingredient” of the drug in

question. In particular, the Food and Drug Administration (FDA) must assess the novelty of the

active ingredient in a new drug, comparing it to a previously approved drug’s active ingredient to determine whether the new

drug qualifies for the five-year “new chemical entity” (NCE) exclusivity. FDA generally cannot accept new drug applications

that refer to a drug with NCE exclusivity (i.e., rely on its clinical data and FDA’s approval of the drug) for five years.

Companies that receive approval for drugs with new active ingredients generally enjoy a competitive advantage in the market

while the exclusivity is in effect—and after, depending how long it takes for generic versions to receive approval once

applications can be submitted.

Comparing active ingredients can be technically quite complicated. For instance, compounds in a final drug product may

convert to other compounds through chemical reactions inside the body before arriving at the site of the therapeutic effect. In

addition, related but distinct drug molecules may be clinically indistinguishable or convert into the same pharmacologically

or physiologically active component inside the body. Alternatively, two drug molecules with the same core compound may

have different compounds appended to them by either covalent or noncovalent bonds. For example, replacing a hydrogen

atom in an acid molecule with “a metal or its equivalent” forms a salt, while replacing the hydrogen atom with “an organic

radical” forms an ester. These derivatives may or may not vary from each other in clinically significant ways. This raises the

question of which derivative(s), if any, should be considered to be the same active ingredient as the core or base molecule.

Generally, a more expansive interpretation of phrase “active ingredient,” that is, one that considers more types of derivatives

to be the same active ingredient, reduces the number of drugs eligible for NCE regulatory exclusivity by expanding the drug

ingredients considered previously approved, which allows for earlier introduction of generic versions of those drugs.

Historically, for the exclusivity provisions, FDA interpreted “active ingredient” to mean “active moiety,” as defined by FDA

regulations. FDA generally defines active moiety as the core molecule or ion of a drug (i.e., the drug molecule without

certain appendages) that is “responsible for the physiological or pharmacological action of a drug substance.” FDA’s

interpretation generated disputes between FDA and pharmaceutical companies, as FDA’s approach tends to exclude some

drugs from being afforded five-year NCE exclusivity under the FD&C Act. In 2015, a federal district court rejected FDA’s

interpretation as inconsistent with the statutory language, though it did not explicitly invalidate FDA’s regulations.

On April 23, 2021, the 117th Congress enacted legislation that generally codified FDA’s long-standing approach to

evaluating NCE exclusivity and extended that approach to certain other provisions under the FD&C Act. This legislation

effectively mooted questions about the validity of FDA’s interpretation and clarified when chemical entities are sufficiently

similar to be considered identical for purposes of drug approval and exclusivity.

Congressional Research Service

Defining Active Ingredient: FDA's Legal Interpretation of Regulatory Exclusivities

Contents

Introduction ..................................................................................................................................... 1

FDA’s Historical Interpretation of Active Ingredient ...................................................................... 2

Challenges to FDA’s Approach ....................................................................................................... 4

FDA’s Interpretation of the Exclusivity Provision .................................................................... 5

FDA’s Definition of Active Moiety .......................................................................................... 11

Legislative Amendment by the 117th Congress ............................................................................ 13

Contacts

Author Information........................................................................................................................ 14

Congressional Research Service

Defining Active Ingredient: FDA's Legal Interpretation of Regulatory Exclusivities

Introduction

Whether many provisions of the Federal Food, Drug, and Cosmetic Act (FD&C Act) apply to a

particular drug product turns in part on the novelty of the “active ingredient” of the drug in

question. In particular, the Food and Drug Administration (FDA) must assess the novelty of the

active ingredient in a new drug, comparing it to a previously approved drug’s active ingredient to

determine whether the new drug qualifies for the five-year “new chemical entity” (NCE)

exclusivity.1 FDA generally cannot accept new drug applications or abbreviated new drug

applications that refer to a drug with NCE exclusivity (i.e., rely on its clinical data and FDA’s

approval of the drug) for five years.2 Companies that receive approval for drugs with new active

ingredients generally enjoy a competitive advantage in the market while the exclusivity is in

effect until generic drugs enter the market.3 Given how expensive it can be to bring a new drug to

market,4 when Congress passed the Hatch-Waxman Amendments in 1984 to allow an abbreviated

pathway for approval of generic drugs, it also created NCE exclusivity to reward innovators of

new pharmaceutical products with an opportunity to recoup their investment.5

To determine whether FD&C Act provisions that depend in part on the drug’s “active ingredient”

apply, FDA must evaluate the “active ingredient(s)” of both the drug under review and any

previously approved drug that may contain the same active ingredient.6 This process can be

technically quite complicated. For instance, compounds in a final drug product may convert to

other compounds through chemical reactions inside the body before arriving at the site of the

therapeutic effect, and related but distinct drug molecules may be clinically indistinguishable or

convert into the same pharmacologically or physiologically active component inside the body.7

This phenomenon raises the question of which molecule—the one existing before or after

ingestion—should be the relevant molecule for purposes of determining active ingredient.8

Alternatively, two drug molecules with the same core compound may have different compounds

appended to them by either covalent (i.e., shared electrons) or noncovalent (i.e., no shared

electrons) bonds.9 For example, replacing a hydrogen atom in an acid molecule with “a metal or

its equivalent” forms a salt, whereas replacing the hydrogen atom with “an organic radical” forms

an ester.10 These derivatives may or may not vary from each other in clinically significant ways,11

1 21 U.S.C. §§ 355(j)(5)(F)(ii) & 355(c)(3)(E)(ii).

2 Id. Abbreviated new drug applications that challenge nonexpired listed patents may be submitted after four years. Id.

3 Generic Competition and Drug Prices, FOOD & DRUG ADMIN. (Nov. 28, 2017), https://www.fda.gov/about-fda/center-

drug-evaluation-and-research-cder/generic-competition-and-drug-prices (finding association between generic

competition and lower drug prices).

4 See generally Joseph A. Di Masi, Henry G. Grabowski, & Ronald W. Hansen, Innovation in the Pharmaceutical

Industry: New Estimates of R&D Costs, 47 J. HEALTH ECON. 20 (2016).

5 See, e.g., King Drug Co. of Florence, Inc. v. Smithkline Beecham Corp., 791 F.3d 388, 394 (3d Cir. 2015) (“Congress

attempted to balance the goal of ‘mak[ing] available more low cost generic drugs, H.R. Rep. No. 98-857, pt. 1, at 14-15

(1984), reprinted in 1984 U.S.C.C.A.N. 2647, 2647-48, with the value of patent monopolies in incentivizing beneficial

pharmaceutical advancement, see H.R. Rep. No. 98-857, pt. 2, at 30 (1984), reprinted in 1984 U.S.C.C.A.N. 2686,

2714.”); Yaniv Heled, Patents v. Statutory Exclusivities in Biological Pharmaceuticals—Do We Really Need Both?, 18

MICH. TELECOMM. & TECH. L. REV. 419, 427-30, 434-36 (2012).

6 See, e.g., 21 U.S.C. § 355(c)(3)(E).

7 See, e.g., Actavis Elizabeth LLC v. FDA, 625 F.3d 760, 762-63, 766 (D.C. Cir. 2010); Abbott Laboratories v. Young,

920 F.2d 984, 986 (D.C. Cir. 1990).

8 See infra “FDA’s Definition of Active Moiety.”

9 Actavis Elizabeth LLC, 625 F.3d at 765-66.

10 Amarin Pharm. Ireland Ltd. v. FDA, 106 F. Supp. 3d 196, 199 n.1 (D.D.C. 2015).

11 Actavis Elizabeth LLC, 625 F.3d at 765-66.

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Defining Active Ingredient: FDA's Legal Interpretation of Regulatory Exclusivities

raising the question of which derivative(s), if any, should be considered as the same active

ingredient as the core or base molecule.12 Generally, a more expansive interpretation of the phrase

“active ingredient,” that is, one that considers more types of derivatives to be the same active

ingredient, reduces the number of drugs eligible for NCE regulatory exclusivity by expanding the

drug ingredients considered previously approved, which, in turn, allows for earlier introduction of

generic versions of those drugs.

As discussed in more detail below, historically, for purposes of the exclusivity provisions, FDA

interpreted “active ingredient,” as the term appears in statute, to mean “active moiety,” as defined

by FDA regulations.13 FDA generally defines active moiety as the core molecule or ion of a drug

(i.e., the drug molecule without certain appendages) that is “responsible for the physiological or

pharmacological action of a drug substance.”14 FDA’s interpretation generated disputes between

FDA and pharmaceutical companies, as FDA’s approach tends to exclude some drugs from being

afforded five-year NCE exclusivity under the FD&C Act.15 In 2015, a federal district court

rejected FDA’s interpretation as inconsistent with the statutory language, though it did not

explicitly invalidate FDA’s regulations.16

On April 23, 2021, the 117th Congress enacted legislation that generally codified FDA’s longstanding approach to evaluating NCE exclusivity and extended that approach to other provisions

under the FD&C Act that formerly included the phrase “active ingredient (including any ester or

salt of the active ingredient).”17

This report discusses FDA’s historical interpretation of the FD&C Act as referring to active

moieties, judicial review of FDA’s interpretation before the legislative amendment, and how

FDA’s rationale changed over time.

FDA’s Historical Interpretation of Active Ingredient

Until the statute was amended in 2021, multiple provisions of the FD&C Act used the phrase

“active ingredient (including any ester or salt of the active ingredient).”18 Among them were a

provision for five-year exclusivity to drugs approved under a new drug application (NDA) with

active ingredients that FDA has not previously approved,19 a provision for three-year exclusivity

for drugs with the same active ingredient as previously approved drugs that required additional

clinical studies for approval due to other changes,20 and provisions authorizing priority review

vouchers for certain types of drugs.21 In the context of the five-year-exclusivity, which FDA has

12 See infra “FDA’s Definition of Active Moiety.”

13 See 21 C.F.R. § 314.3; 59 Fed. Reg. 50,338, 50,357-58, 50,368-69 (Oct. 3 1994).

14 21 C.F.R. § 314.3(b).

15 See generally, Actavis Elizabeth LLC v. FDA, 625 F.3d 760 (D.C. Cir. 2010); Abbott Labs. v. Young, 920 F.2d 984

(D.C. Cir. 1990); Otsuka Pharm. Co. v. Burwell, 302 F. Supp. 3d 375 (D.D.C. 2016); Ferring Pharm., Inc. v. Burwell,

169 F. Supp. 3d 199 (D.D.C. 2016).

16 Amarin Pharm. Ireland Ltd. v. FDA, 106 F. Supp. 3d 196, 217-19 (D.D.C. 2015).

17 S. 1636, 116th Cong. (2019); S. 1895, 116th Cong. § 208 (2019).

18 21 U.S.C. § 355(c)(3)(E)(i),(ii), (iii) & (v); id. § 355(j)(5)(F)(i), (ii), (iii) & (v); id. § 355(l)(2)(A)(i); id. § 355(s); id.

§ 355(u)(1); id. § 360b(c)(2)(F)(i), (ii), and (v); id. § 360n(a)(4)(C); id. § 360ff(a)(4)(A)(ii); & id. § 360bbb4a(a)(4)(D).

19 21 U.S.C. § 355(c)(3)(E)(ii) & (j)(5)(F)(ii).

20 Id. § 355(c)(3)(E)(iii) & (j)(5)(F)(iii).

21 Id. §§ 360ff(a)(4)(A)(ii), 360n(a)(4)(C), 360bbb-4a(a)(4)(D).

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coined “new chemical entity” or NCE exclusivity,22 FDA interpreted the term “active ingredient”

to mean “active moiety.”23 FDA reasoned that this definition, which allows a wider range of

molecules to be considered previously approved, was warranted in the new drug context to

encourage innovation by ensuring that a new drug is truly innovative.24 This interpretation of

“active ingredient” in the NCE exclusivity context was the subject of a decades-long debate.

Before its amendment, the statutory provision on NCE exclusivity stated, in relevant part,

If an application submitted under subsection (b) of this section for a drug, no active

ingredient (including any ester or salt of the active ingredient) of which has been approved

in any other application under subsection (b) of this section, is approved ... no application

may be submitted under this subsection which refers to the drug for which the subsection

(b) application was submitted before the expiration of five years from the date of approval

of the application under subsection (b) of this section.... 25

Disputes over how FDA should interpret this provision centered on the meaning of the phrase

“active ingredient (including any ester or salt of the active ingredient).”26 The FD&C Act did not

define the term “active ingredient.”27 Rather than define “active ingredient” for purposes of the

exclusivity provisions, FDA examined the relevant drugs’ active moieties.28 Specifically, FDA

defines NCE exclusivity in its regulations as “a drug that contains no active moiety that has been

approved by FDA in any other application submitted under section 505(b) of the act.”29 The

various other exclusivity regulations also refer to active moieties.30

FDA defines “active moiety” in its regulations as follows:

Active moiety is the molecule or ion, excluding those appended portions of the molecule

that cause the drug to be an ester, salt (including a salt with hydrogen or coordination

22 Id. § 355(j)(5)(F)(ii); 21 C.F.R. § 314.108. See also 21 U.S.C. § 355(c)(3)(E)(ii) & (iii), 355(j)(5)(F)(iii). The three-

year exclusivity for drugs with previously approved active ingredients that require additional clinical studies to be

approved (e.g., for new indications or methods of use) includes similar statutory language and has been similarly

interpreted by FDA to refer to active moieties. See 21 U.S.C. § 355(j)(5)(F)(iii) & (iv); 21 C.F.R. § 314.108.

23 21 C.F.R. § 314.108.

24 Abbreviated New Drug Application Requirements; Patent and Exclusivity Provisions, 59 Fed. Reg. 50,338, 50,358

(Oct. 3, 1994).

25 21 U.S.C. § 355(j)(5)(F)(ii) (emphasis added). See also id. § 355(c)(3)(E)(ii).

26 See, e.g., Amarin Pharm. Ireland Ltd. v. FDA, 106 F. Supp. 3d 196, 206-07 (D.D.C. 2015); Actavis Elizabeth LLC v.

FDA, 625 F.3d 760, 761-62 (D.C. Cir. 2010); Abbott Labs. v. Young, 920 F.2d 984, 985-86 (D.C. Cir. 1990). “Esters

and salts are molecules that form in chemical reactions when the hydrogen atom of an acid molecule is replaced by

another substance.” Amarin Pharm. Ireland Ltd., 106 F. Supp. 3d at 199.

27 FDA did not define “active ingredient” when it originally enacted regulations to implement the Hatch-Waxman

Amendments. See generally 59 Fed. Reg. 50,338. However, it did define the term outside of the exclusivity context in

2016 when implementing the Medicare Prescription Drug, Improvement, and Modernization Act of 2003. See 81 Fed.

Reg. 69,580, 69,580, 69,637 (Oct. 6, 2016). FDA regulations now define “active ingredient” as

[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[,] includ[ing] those components that may undergo

chemical change in the manufacture of the drug product and be present in the drug product in a

modified form intended to furnish the specified activity or effect.

21 C.F.R. § 314.3. However, FDA has not changed its approach to NCE exclusivity, as the agency continues to

examine the active moiety of the relevant drugs. See id. § 314.108.

28 See, e.g., 54 Fed. Reg. 28,872, 28,896-98 (July 10, 1989); 59 Fed. Reg. 50,338, 50357-58, 50,368-69 (Oct. 3 1994);

New Chemical Entity Exclusivity Determinations for Certain Fixed-Combination Drug Products: Guidance for

Industry, U.S. DEP’T OF HEALTH AND HUMAN SERV., FOOD & DRUG ADMIN. (2014).

29 21 C.F.R. § 314.108(a) (emphasis added).

30 Id. § 314.108(b)(2) & (4).

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bonds), or other noncovalent derivative (such as a complex, chelate, or clathrate) of the

molecule, responsible for the physiological or pharmacological action of the drug

substance.31

Key Terms

Ester. An organic compound formed by reaction between alcohols and acids.

Salt. A chemical compound formed by reaction of an acid with a base, in which the hydrogen of the acid has been

replaced by metal or other positive ions.

Covalent bond. A chemical bond created by sharing electrons.

Noncovalent bond. A chemical bond that does not entail sharing electrons.

Source: Rennie, R., & Law, J. (Eds.), A Dictionary of Chemistry. Oxford University Press.

As one court put it, “[f]or salts, esters, and noncovalent derivatives, a molecule’s ‘active moiety’

can be thought of as its core; salt, ester and noncovalent derivative versions of the same basic

molecule have different appendages, but they share the same active moiety.”32 Put another way,

because these specified derivatives would be considered to have the same “active moiety,” if FDA

approved a drug containing any one of the specified derivatives as the active ingredient, a later

approved drug containing another form of a specified derivative or even the core molecule would

not be entitled to NCE exclusivity.

For instance, under this approach (which has subsequently been codified in legislation), if Drug A

contains as its active ingredient a salt, ester, or other noncovalent derivative of a molecule that

FDA previously approved as part of Drug B, Drug A would not be entitled to NCE exclusivity

because FDA had previously approved that active moiety.33 Similarly, if Drug B contains as its

active ingredient a salt derivative of a molecule, and Drug A contains that same molecule or an

ester derivative of that molecule and is approved after Drug B, Drug A would not be entitled to

NCE exclusivity.34 In contrast, if Drug A contained as its active ingredient a non-ester covalent

derivative of a molecule that FDA previously approved in Drug B, Drug A could be considered to

have a new active moiety and be eligible for NCE exclusivity if other relevant conditions are met.

If a drug molecule is converted to a different but related compound after ingestion, under this

interpretation of the FD&C Act, the relevant molecule for determining active moiety is the

compound in the final drug product before the drug is ingested.

Challenges to FDA’s Approach

In the NCE exclusivity context, FDA’s interpretation of “active ingredient” as “active moiety,” as

well as its definition of “active moiety,” were both subject to dispute. Challenges to FDA’s

approach to NCE exclusivity generally addressed two questions:

1. Whether FDA could permissibly interpret the phrase “no active ingredient

(including any ester or salt of the active ingredient) of which has been approved”

as “a drug that contains no active moiety that has been approved.”35

31 Id. § 314.3.

32 Amarin Pharm. Ireland Ltd. v. FDA, 106 F. Supp. 3d 196, 199-200 (D.D.C. 2015).

33 21 U.S.C. §§ 355(c)(3)(E)(ii) & (iii), 355(j)(5)(F)(iii).

34 21 C.F.R. § 314.108.

35 Related to this question is what language FDA has determined to be ambiguous to allow room for FDA’s

interpretation.

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2. Whether FDA correctly defined “active moiety,” including whether FDA may

permissibly deny exclusivity for—in addition to “salts and esters,” which appear

in the statute—other noncovalent derivatives of the underlying drug molecule.36

FDA’s Interpretation of the Exclusivity Provision

Proposed Rule. In 1989, in its implementing regulations for the Hatch-Waxman Amendments,

FDA first interpreted the FD&C Act’s exclusivity provisions to distinguish between NCEs, which

are entitled to a five-year term of regulatory exclusivity, and previously approved active

ingredients, which are entitled to three years of regulatory exclusivity, based on active moieties.37

To support its interpretation in the proposed rule, the agency relied on the statutory text, FDA’s

preexisting classification scheme for drugs that included a “new molecular entity” class based on

active moieties, and the legislative history of the Hatch-Waxman Amendments.38 FDA reasoned

that “Congress was aware of FDA’s classification scheme” when it passed the Hatch-Waxman

Amendments, including FDA’s “longstanding interpretation of the term ‘new molecular entity’

[as] a compound containing an entirely new active moiety.”39 In support of its definition of active

moiety, which includes other noncovalent derivatives of a drug molecule in addition to the drug

molecule itself and its salt and esters, FDA reasoned that Congress “did not intend to confer

significant periods of exclusivity on minor variations of previously approved chemical

compounds.”40 FDA did not specifically identify which part of the statutory phrase “an active

ingredient (including any ester or salt of the active ingredient)” it had determined to be

ambiguous when adopting the interpretation of “active moiety.”41

Initial Litigation Rejecting FDA Approach. Between FDA’s proposed rule in 1989 and its final

rule in 1994 implementing the exclusivity regulations, two cases addressed the agency’s

interpretation of the phrase “active ingredient (including any ester or salt of the active

ingredient)” to mean active moiety. In Abbott Laboratories v. Young, the U.S. Court of Appeals

for the D.C. Circuit (D.C. Circuit) considered FDA’s denial of 10-year exclusivity42 for Depakote,

an anticonvulsant seizure medication that used divalproex sodium as its active ingredient.43 FDA

based its decision on findings that (1) divalproex sodium is a salt of valproic acid that converts

into valproic acid in the body, and (2) the agency previously approved valproic acid as the active

ingredient in Depakene.44 The court determined that the FD&C Act’s use of the phrase “the active

36 Related to this question is whether the term active moiety must include other covalent derivatives that convert into

the same compound to achieve the therapeutic effect.

37 See, e.g., 54 Fed. Reg. at 28,896-98; 59 Fed. Reg. at 50357-58, 50,368-69.

38 54 Fed. Reg. at 28,897-98.

39 Id.

40 Id. at 28,898.

41 Under the Chevron doctrine, established by the Supreme Court in Chevron U.S.A. v. Natural Resources Defense

Council, when reviewing agency interpretations of statutes, the court first asks “whether Congress has directly spoken

to the precise question at issue.” 467 U.S. 837, 842 (1984). “If so, the court must ‘give effect to the unambiguously

expressed intent of Congress.’” Amarin Pharm. Ireland Ltd., 106 F. Supp. 3d at 205 (quoting Chevron U.S.A., 467 U.S.

at 843). Only if the court “concludes that Congress has left an ambiguity or ‘gap’ to fill on the ‘precise question at

issue’” does the court proceed to ask “whether the agency’s construction of the statute is a ‘permissible’ one,” in which

case the court defers to the agency. Id. at 206. Finding ambiguity in the statutory provision accordingly allows the court

to consider FDA’s interpretation.

42 For drugs approved between January 1, 1982, and September 24, 1984 (before the Hatch-Waxman Amendments

were passed), Congress provided a 10-year period of exclusivity for drugs with new chemical entities and a 2-year

period of exclusivity for all other drugs. 21 U.S.C. § 355(j)(5)(F).

43 920 F.2d 984, 986 (D.C. Cir. 1990).

44 Id.

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ingredient” is ambiguous, as it could refer to the active ingredient in the original approved drug or

in the later approved drug.45 However, the D.C. Circuit rejected FDA’s reliance on the term

“including” to justify using its definition of active moiety, which extends beyond salts and esters

of the active ingredient to other noncovalent derivative molecules, as “linguistically infeasible.”46

Specially, the court concluded that Congress used the term “including” in the provision at issue

not to provide examples of molecular derivatives undeserving of regulatory exclusivity but to

extend the covered active ingredients to the two particular derivatives—esters and salts.47 Upon

concluding that the statute is ambiguous and that FDA failed to provide a reasonable construction,

the D.C. Circuit remanded the case to FDA for further actions.48

Around the same time, the U.S. Court of Appeals for the Federal Circuit (Federal Circuit)

considered the U.S. Patent and Trademark Office’s (USPTO’s) denial of Glaxo’s request for a

patent-term extension for its patent claiming cefuroxime axetil, the active ingredient in Ceftin

tablets.49 The Hatch-Waxman Amendments require the USPTO to extend the terms of a patent

claiming a product or a method of using or manufacturing a product when (1) the product is

“subject to a regulatory review period” (e.g., the FDA drug approval process) and (2) the

permission to market the product following the regulatory review (e.g., FDA approval of the

drug) is the “first permitted commercial marketing or use of the product.”50 In turn, the statute

defines “product” to mean “the active ingredient of a new drug ... including any ester or salt of

the active ingredient.”51 Interpreting the product as the active moiety, the USPTO found that

cefuroxime (an acid) rather than cefuroxime axetil (an ester of cefuroxime) was the active moiety

in Ceftin.52 Because FDA had previously approved two drugs with cefuroxime salts as active

ingredients,53 the USPTO determined that FDA’s approval of Ceftin was not the “first permitted

commercial marketing or use of the product” and denied the patent-term extension.54

The Federal Circuit held that the USPTO’s denial of the patent term extension was contrary to

law, affirming the district court’s judgment.55 In contrast to the D.C. Circuit, which viewed the

relevant statutory language as ambiguous, the Federal Circuit held that the terms in the phrase

“active ingredient of a new drug ... including any ester or salt of the active ingredient” all have a

plain meaning.56 The court determined—without discussing its reasoning in any detail—that the

USPTO’s interpretation was inconsistent with the plain meaning of these terms.57 While

acknowledging that legislative history can reveal “a clearly expressed legislative intention

contrary to the statutory language,” it identified no such support for the USPTO’s interpretation

here.58 Because the court found there was no clear legislative intent that the phrase be interpreted

to refer to variations on the approved active ingredients beyond that product’s ester or salt, an

45 Id. at 987-88.

46 Id. at 988.

47 Id.

48 Id. at 989-90.

49 Glaxo Operations UK Ltd. v. Quigg, 894 F.2d 392, 393-94 (Fed. Cir. 1990).

50 35 U.S.C. § 156(a) & (f).

51 Id. § 156(f)(2).

52 Glaxo Operations UK Ltd., 894 F.2d at 394.

53 Glaxo Operations UK Ltd. v. Quigg, 706 F. Supp. 1224, 1225-26 (E.D. Va. 1989).

54 Glaxo Operations UK Ltd., 894 F.2d at 394.

55 Id. at 399-400.

56 Id. at 395.

57 Id.

58 Id. at 395-400.

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extension of the term for the patent claiming cefuroxime axetil was warranted because FDA had

not approved that drug product or an ester or salt of it.59 While the appellate court did not

elaborate on how it arrived at its interpretation, the district court had included more detail on the

plain meaning of the operative statutory phrase, concluding that cefuroxime—the acid from

which cefuroxime axetil is derived—could not be an “active ingredient” of Ceftin because it was

not an ingredient, as that term is commonly understood because it did not appear in the Ceftin

tablets in that form.60

Final Rule. In the wake of these rulings, public comments to FDA’s proposed rule contended that

Abbott Laboratories and Glaxo Operations rejected the agency’s proposed interpretation of the

NCE exclusivity provision, particularly its reliance on the phrase active moieties.61 Nonetheless,

when FDA finalized its NCE exclusivity regulations in 1994, the agency included its proposed

definition of “active moiety,” but modified its justification.62 Rather than interpreting the

parenthetical phrase (i.e., “(including any ester or salt of the active ingredient)”) “broadly to

include all active ingredients that are different but contain the same active moiety,” which the

D.C. Circuit in Abbott Laboratories had rejected as “linguistically impermissible,” the agency

concluded that the term “active ingredient,” as used in the relevant provision, means active

moiety.63 FDA did not, however, directly address the Federal Circuit’s opinion.

FDA also disagreed with comments objecting to its inclusion of other noncovalent derivatives in

the definition of “active moiety,” meaning that such derivatives would not receive NCE

exclusivity. The agency reaffirmed that it “does not believe that providing exclusivity for ...

noncovalent derivatives of a previously approved active moiety would be consistent with the

statutory intent” because such derivatives “generally do[] not affect the active moiety of a drug

product.”64 FDA accordingly enacted the definition of active moiety as proposed.

D.C. Circuit Upholds FDA Use of Pre-Ingestion Rather than Post-Ingestion to Interpret

Active Ingredient. In 2010, in Actavis Elizabeth LLC v. FDA, the D.C. Circuit revisited FDA’s

interpretation of “active ingredient,” nearly two decades after the agency finalized its regulations

in 1994.65 That opinion focused specifically on the term “active ingredient” in the context of

whether the relevant molecule should be considered prior to its ingestion in the human body (i.e.,

the compound in the final drug product pre-ingestion) or after ingestion where the compound may

convert to another related compound (e.g., from an ester to an acid) that is responsible for the

drug’s therapeutic effects (i.e., post-ingestion).66 A generic manufacturer challenged FDA’s award

of NCE exclusivity for Vyvanse, a drug that treats attention deficit hyperactivity disorder.67

Vyvanse’s active ingredient is lisdexamfetamine dimesylate, a salt of lisdexamfetamine, meaning

59 Id. at 395-99.

60 Glaxo Operations UK Ltd. v. Quigg, 706 F. Supp. 1224, 1227-28 (E.D. Va. 1989).

61 59 Fed. Reg. 50,338, 50,357-58 (Oct. 3, 1994).

62 Id.

63 Id.

64 Id. at 50,358.

65 Actavis Elizabeth LLC v. FDA, 625 F.3d 760, 764-66 (D.C. Cir. 2010).

66 Id. Note that the court in Abbott Laboratories v. Young had explained the distinction between active ingredient and

active moiety as the former being “the substance prior to introduction into the human body” and the latter being “the

substance that creates the actual therapeutic effect within the body.” 920 F.2d 984, 986 (D.C. Cir. 1990). While this

distinction may be accurate for some drugs if the active ingredient converts to the active moiety inside the body, this

explanation is not fully consistent with FDA’s regulatory definition of “active moiety” or with FDA’s analysis in

practice. See, e.g., Actavis Elizabeth LLC v. FDA, 625 F.3d 760, 764-66 (D.C. Cir. 2010).

67 Actavis Elizabeth LLC, 625 F.3d at 762.

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that lisdexamfetamine is the active moiety under FDA regulations.68 Lisdexamfetamine uses an

amide bond (a type of covalent bond involving nitrogen) to connect a portion of lysine, a

common amino acid, with dextroamphetamine.69 Once in the body, a chemical reaction converts

lisdexamfetamine to dextroamphetamine.70 FDA had approved drugs with dextroamphetamine

but had not yet approved drugs with lisdexamfetamine.71

Actavis, a generic manufacturer seeking to market a generic version of Vyvanse, alleged that

because dextroamphetamine is responsible for the therapeutic effect inside the body and FDA had

previously approved drugs with dextroamphetamine, Vyvanse had no right to NCE exclusivity.72

Focusing on the term “active,” Actavis contended that “active ingredient” necessarily must refer

to “the drug molecule that reaches the ‘site’ of the drug’s action” because that is the part of the

drug responsible for its “activity,” which Actavis argued meant the therapeutic effect.73

The court rejected Actavis’s arguments. First, the court observed that the FD&C Act does not

define the term “active ingredient” and that the statute’s legislative history “is silent on what

determines novelty” for NCE exclusivity.74 The court also concluded that the statute’s structure

and purpose did not preclude FDA’s interpretation.75 Accordingly, the court held that (1) “active

ingredient” was ambiguous as to whether it referred to the pre-ingestion or post-ingestion

molecule, and (2) FDA’s interpretation of “active ingredient” to refer to the pre-ingestion

molecule was reasonable.76

The court further affirmed FDA’s choice of a bright-line distinction between noncovalent

derivatives (which do not receive NCE exclusivity) and non-ester covalent derivatives (which can

receive NCE exclusivity and was at issue for Vyvance). While the D.C. Circuit acknowledged that

some noncovalent bonds might alter a drug’s properties and some covalent bonds might not,77 the

court deferred to FDA’s explanation that “its policy is based in part on the ‘difficulty in

determining precisely which molecule, or portion of a molecule, is responsible for a drug’s

effects.’”78 The court did not, however, directly address FDA’s use of the term “active moiety,” its

inclusion of the other noncovalent derivatives in the definition, or the interaction between FDA’s

definition of active moiety and the statutory parenthetical.

District Court Rejects FDA Interpretation of Active Ingredient as Active Moiety. Five years

later, in Amarin Pharmaceuticals Ireland Ltd. v. FDA, a federal district court in the District of

Columbia expressly considered FDA’s interpretation of “active ingredient” to mean “active

moiety,” as defined in its regulations.79 Amarin had obtained FDA approval for Vascepa, whose

active ingredient is icosapent ethyl, the ethyl ester of eicosapentaenoic acid (EPA), a type of

omega-3 fatty acid.80 But FDA denied Amarin’s request for NCE exclusivity for Vascepa because

68 Id. at 762-63.

69 Id. at 763.

70 Id.

71 Id.

72 Id. at 762.

73 Id.

74 Id.

75 Id.

76 Id. at 765-66.

77 Id. at 766.

78 Id.

79 106 F. Supp. 3d 196, 208 (D.D.C. 2015).

80 Id. at 202.

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it had previously approved Lovaza, a drug whose active ingredient is “a mixture that is primarily

composed of seven kinds of omega-3 fatty acid ethyl esters” including the ester of EPA.81 When

FDA approved Lovaza, it considered the mixture as a whole the “active ingredient,” and it later

denied a petition from Lovaza’s sponsor requesting FDA to recharacterize Lovaza as having

multiple active ingredients on the grounds that “the Lovaza mixture has not been ‘fully

characterized.’”82 In other words, in approving Lovaza, FDA did not specifically approve an ester

of EPA (or any other component omega-3 fatty acid ethyl esters) as an active ingredient. But

when evaluating Vascepa’s eligibility for NCE exclusivity, FDA relied on new studies to find that

EPA was an active moiety of Lovaza and that, accordingly, FDA had previously approved

Vascepa’s active moiety.83

Rather than recognize multiple active ingredients in Vascepa, FDA provided a new interpretation

framework for certain mixtures to treat them as having one active ingredient but multiple active

moieties. In its decision letter to Amarin, FDA acknowledged that the agency had previously

taken an inconsistent approach to identifying the active ingredients and active moieties for

naturally derived mixtures, such as Lovaza, when evaluating NCE exclusivity.84 FDA “explained

that, although they are often conflated, it is important to distinguish between the meaning of the

terms active ingredient and active moiety.”85 Also, while “the distinction between active moiety

and active ingredient[] generally is negligible” for “drugs that are composed of a single, wellcharacterized molecule,” “the distinction between active ingredient and active moiety ... becomes

crucial” “[f]or naturally derived mixtures comprising multiple molecules.”86

Critically, the agency distinguished between (1) “poorly characterized” and (2) “wellcharacterized mixtures” based on how difficult it is “‘to determine with any certainty ... which

molecules in the mixture are consistently present or potentially are responsible for the

physiological or pharmacological activity of the drug.’”87 For poorly characterized mixtures,

FDA stated that it had “of necessity” treated the whole mixture as both the active ingredient and

the active moiety.88 However, for well-characterized mixtures, FDA outlined “a three-part

‘framework’ ‘for identifying the active moiety or moieties of such mixtures.’”89 FDA would

consider component parts of well-characterized mixtures to be previously approved active

moieties if

1. specific molecules in the mixture have been identified;

2. those specific molecules are “consistently present in the mixture”; and

3. those molecules are “responsible at least in part for the physiological or

pharmacological action of the mixture, based on a finding that they make a

meaningful contribution to the activity of the mixture.”90

81 Id. at 201.

82 Id.

83 Id. at 203-04.

84 Id. at 203.

85 Id. at 204 (internal quotations omitted) (referencing FDA decision letter).

86 Id. (internal quotations omitted).

87 Id.

88 Id.

89 Id.

90 Id.

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In effect, for single-molecule and poorly characterized drugs, FDA would apply a one-to-one

approach between the active ingredient and active moiety, but for well-characterized mixtures, it

would apply a one-to-many approach: one active ingredient with multiple active moieties.91

The district court set aside FDA’s decision denying NCE exclusivity for Vascepa based on its

interpretation of “active ingredient” to mean “active moiety”.92 The court first relied on the canon

against surplusage, finding that FDA’s interpretation of the term “active ingredient” “would

render the parenthetical clause in the exclusivity provisions either redundant or

incomprehensible.”93 By defining active moiety to exclude “those appended portions of the

molecule that cause the drug to be an ester, salt ... or other noncovalent derivative,”94 the court

concluded that FDA rendered the statutory parenthetical “(including any ester or salt of the active

ingredient)” either unnecessary or incomprehensible.95 The court reasoned that FDA in effect read

the parenthetical out of the statute by inserting “active moiety” in place of “active ingredient,”

violating the canon against surplusage that assumes Congress does not include unnecessary

language in a statute.96

The court then used the presumption of consistent usage to reject FDA’s view of active ingredient

as synonymous with active moiety.97 Significantly, FDA only interpreted active ingredient to

mean active moiety with respect to the FD&C Act’s exclusivity provisions, relying on alternative

interpretations of “active ingredient” elsewhere in the statute, such as, perhaps most notably, the

provision allowing sponsors to submit abbreviated NDAs for generic drugs with the same active

ingredient as an approved drug.98 FDA argued that it was justified in adopting different

interpretations of the same phrase in different parts of the statute because the provisions had

different statutory purposes.99 The agency contended that because the abbreviated NDA process

focuses on safety and efficacy, a narrower range of molecules should be considered identical to

previously approved drugs to ensure that FDA conducts a full review for safety and efficacy of

any drugs that may clinically differ from previously approved drugs.100 In contrast, FDA argued

that the exclusivity provisions aim to encourage innovation, requiring a wider range of molecules

to be considered previously approved to ensure the new drug is truly innovative.101

While acknowledging that “the presumption of consistent usage is not unrebuttable,” the court

considered FDA’s justifications for the differing interpretations of active ingredient

unpersuasive.102 The court observed that Congress passed both provisions at the same time in the

same part of the same statute, that the abbreviated NDA provisions and exclusivity provisions

were two sides of the same coin intended to balance competition and innovation, and that

91 Id. at 204-205.

92 Id. at 217-19.

93 Id. at 209.

94 21 C.F.R. § 314.3.

95 Amarin Pharm. Ireland Ltd. v. FDA, 106 F. Supp. 3d 196, 209 (D.D.C. 2015).

96 Id. FDA offered an alternative interpretation that active moiety replaced the entire phrase “an active ingredient

(including any ester or salt of the active ingredient)” rather than simply “active ingredient.” Id. at 215-16. The court

rejected this interpretation as well. Id. First, the court found that FDA had not relied on this interpretation in either its

final rule or its decision letter. Id. Second, the court determined that this interpretation raises the same issues identified

by the D.C. Circuit in Abbott Laboratories v. Young. Id.

97 Id. at 210.

98 Id.

99 Id. at 210-11.

100 Id.

101 Id.

102 Id. at 211-12.

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Congress included the parenthetical “including any ester or salt of the active ingredient” in the

exclusivity provision but not the abbreviated NDA provision, thus already distinguishing between

the two provisions.103

Finally, the court determined that FDA’s use of active moiety was inconsistent with the statutory

requirement that the active ingredient “has been approved.”104 It noted that FDA approves active

ingredients, not active moieties, and that under FDA’s proposed framework it would not even

determine the relevant active moiety under another drug applied for exclusivity.105 Accordingly,

an active moiety would never have previously been approved.106

Rejecting each of FDA’s arguments and concluding FDA’s interpretation invalid on multiple

grounds, the court set aside the specific administrative decision being challenged in that case—

that is, FDA’s exclusivity determination for Vascepa—and remanded to FDA.107 The court did

not, however, explicitly invalidate or set aside FDA’s implementing regulations.108 FDA

regulations therefore remain in place, but with questions looming as to their validity and

defensibility.109

FDA’s Definition of Active Moiety

Beyond whether FDA can interpret the phrase “active ingredient” in the FD&C Act’s exclusivity

provisions to mean active moiety, how FDA has defined “active moiety” has also been the subject

of legal challenges. (Although Congress amended the FD&C Act, as detailed below, FDA’s

regulatory definition of “active moiety” has not changed.) The statutory parenthetical includes

esters and salts of an active ingredient as the same active ingredient for determining exclusivity,

meaning that an ester and salt of an active ingredient is ineligible for exclusivity.110 FDA’s

definition of active moiety extends beyond those two derivatives, however, to also include

molecules with other noncovalent appendages.111 At the same time, the agency excludes from its

definition of active moiety molecules with appendages attached through non-ester covalent

bonds, meaning that drug molecules that differ from previously approved drugs based on such

appendages would be eligible for NCE exclusivity.112 Brand name manufacturers have challenged

including other noncovalent derivatives, which limits the availability of NCE exclusivity, while

generic manufacturers have challenged excluding non-ester covalent derivatives, which expands

the availability of NCE exclusivity.

103 Id.

104 Id. at 213.

105 Id. at 214.

106 Id.

107 Id. at 219. On remand, FDA determined that Vascepa was eligible for NCE exclusivity. Letter from Janet

Woodcock, Director, Center for Drug Evaluation and Research, Food & Drug Admin, to Robert A. Dormer, Hyman,

Phelps & McNamara, P.C. (Counsel for Amarin Pharmaceuticals Ireland Ltd.) (May 31, 2016)

http://www.fdalawblog.net/wp-content/uploads/archives/docs/VASCEPA%20-%20Exclusivity%20Determination%

20on%20Remand.pdf (conveying decision on exclusivity for Vascepa (icosapent ethyl) capsules (NDA 202057)).

108 See Letter from Janet Woodcock to Robert A. Dormer, supra note 107, at 13.

109 Watson Laboratories filed an appeal, but the D.C. Circuit dismissed the appeal on the grounds that the district court

order remanding the decision to FDA was not a final appealable order. Amarin Pharm. Ireland Ltd. v. FDA, No. 155214, 2015 WL 9997417 (D.C. Cir. 2015).

110 21 U.S.C. §§ 355(c)(3)(E)(ii), 355(j)(5)(F)(ii).

111 21 C.F.R. § 314.3.

112 Id.

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Defining Active Ingredient: FDA's Legal Interpretation of Regulatory Exclusivities

Other Derivatives with Noncovalent Bonds. As discussed above, Abbott Laboratories v. Young

also addressed FDA’s inclusion of other noncovalent derivative forms of the molecule in addition

to salts and esters, which the statute explicitly includes.113 At the time, FDA relied on a broad

interpretation of the word “including” to justify examining the base molecule without salts, esters,

or any other component connected by noncovalent bonds.114 The agency viewed the term

“including” as providing examples of molecules that would be considered minor modifications

that do not merit five-year NCE exclusivity, rather than an exhaustive list.115 While the Abbott

Laboratories court considered FDA’s approach defensible on policy grounds, it considered the

agency’s approach “linguistically infeasible.”116 It stated that it “cannot agree with [FDA’s]

unconvincing attempts to employ the ‘including’ clause to cover all possible permutations of

active ingredient,” distinguishing the NCE exclusivity “including” clause “from instances where

an ‘including’ clause is designed to merely illustrate a few examples of the general category.”117

Rather than provide its own interpretation, however, the court remanded the decision to FDA.118

FDA subsequently modified its interpretation of the statutory language in its 1994 final

regulations. Rather than interpret the parenthetical phrase, the agency concluded that the term

“active ingredient” means “active moiety,” as defined in its regulations.119 In so doing, FDA

reaffirmed its view that allowing NCE exclusivity for other noncovalent derivatives would be

inconsistent with statutory intent.120

In 2015, as explained above, Amarin Pharmaceuticals Ireland Ltd. v. FDA rejected FDA’s revised

interpretation.121 However, because the court only set aside the challenged agency action at issue

in that case without invalidating FDA regulations, FDA regulations remain in force with its

original definition of “active moiety.”122

Derivatives with Non-Ester Covalent Bonds. As discussed above, in Actavis Elizabeth LLC v.

FDA, the D.C. Circuit upheld FDA’s decision to exclude derivatives with different covalent bonds

from its definition of active moiety.123 Unlike noncovalent bonds, covalent bonds entail the

sharing of electrons between molecules, which tends to create a stronger bond.124 The court held

that FDA’s policy was reasonably “based on its view that drug derivatives containing non-ester

covalent bonds are, on the whole, distinct from other types of derivative drugs such that the

former are uniquely deserving of ‘new chemical entity’ status and the resulting five-year

exclusivity.”125 In particular, the court pointed to a 1989 response letter from FDA to a citizen

petition. In that letter, the agency explained that “even minor covalent structure changes are

capable of producing not only major changes in the activity of the drug but changes that are not

readily predicted.” Nonetheless, FDA observed that “the formation of a salt ... or of an ester, is

not intended to, and generally cannot, alter the basic pharmacologic or toxicologic properties of

113 920 F.2d 984, 988 (D.C. Cir. 1990).

114 Id. at 987.

115 Id. at 987-88.

116 Id. at 988.

117 Id.

118 Id. at 989-90.

119 59 Fed. Reg. 50,338, 50,358.

120 Id.

121 Amarin Pharm. Ireland Ltd. v. FDA, 106 F. Supp. 3d 196, 217-19 (D.D.C. 2015).

122 Id. at 219.

123 625 F.3d 760, 765-66 (D.C. Cir. 2010).

124 HARVEY LODISH ET AL., MOLECULAR CELL BIOLOGY §§ 2.1 & 2.2 (4th ed. 2000).

125 Actavis Elizabeth LLC, 625 F.3d at 765-66.

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the molecule.”126 Accordingly, without holding directly on whether FDA reasonably included

other noncovalent derivatives in its active moiety definition, the court held that FDA’s exclusion

of non-ester covalent derivatives was reasonable.127

Legislative Amendment by the 117th Congress

Against this backdrop of decades of complex litigation over FDA’s interpretation of active

ingredient, the 117th Congress enacted legislation that addressed this issue.128 The law generally

(1) codified FDA’s interpretation that eligibility for NCE exclusivity is based on the drug’s active

moiety and (2) incorporated FDA’s definition of active moiety by reference.129 Specifically, the

law replaced the entire phrase “active ingredient (including any ester or salt of the active

ingredient)” with “active moiety (as defined by the Secretary in section 314.3 of title 21, Code of

Federal Regulations (or any successor regulations))” wherever it is found, except for a few

expired provisions that the legislation repealed instead.130 This change amended several FD&C

Act provisions, including the NCE exclusivity provision, three-year exclusivity for other changes,

and provisions providing priority review vouchers for tropical disease treatments, rare pediatric

disease treatments, and countermeasures for agents that threaten national security. 131

Adopting this interpretation resolved certain legal uncertainties under existing case law. In

Amarin Pharmaceuticals v. FDA, the court had rejected FDA’s interpretation but had not

explicitly invalidated FDA’s regulations.132 Though it left FDA’s interpretation in place, the

court’s decision left uncertain FDA’s ability to defend its interpretation going forward. The

enacted legislation addressed these questions by adopting FDA’s interpretation into law.

The enacted legislation also resolved the questions that had been raised as to whether FDA’s

decision to include other noncovalent derivative forms of the molecule in its definition of active

moiety, but not other covalent derivatives, accorded with congressional intent and a justifiable

distinction. The law both adopted FDA’s approach, by incorporating FDA’s definition, and

allowed FDA to modify its approach going forward as its understanding changed, by including

any successor regulations.133 In effect, the law committed the decision as to which molecules

should be deemed effectively the same and therefore not innovative enough to merit NCE

exclusivity to FDA’s judgment.

126

Id.

127 Id.

128 Pub. L. No. 117-9, 135 Stat. 256 (2021).

129 Id.

130Id. Specifically, the law amended 21 U.S.C. § 355(c)(3)(E)(ii) & (iii); 21 U.S.C. § 355(j)(5)(F)(ii) & (iii); 21 U.S.C.

§ 355(l)(2)(A)(i); 21 U.S.C. § 355(s); 21 U.S.C. § 355(u)(1); 21 U.S.C. § 360b(c)(2)(F)(i), (ii), and (v); 21 U.S.C.

§ 360n(a)(4)(C); 21 U.S.C. § 360ff(a)(4)(A)(ii); and 21 U.S.C. § 360bbb-4a(a)(4)(D).

131 S. 1636; S. 1895; H.R. 4955.

132 106 F. Supp. 3d 196, 219 (D.D.C. 2015). See also supra note 108.

133 S. 1636; S. 1895; H.R. 4955.

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Author Information

Erin H. Ward

Legislative Attorney

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Congressional Research Service

R46110 · VERSION 2 · UPDATED

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