Letters RESEARCH LETTER

Variations in Time of Market Exclusivity Among Top-Selling Prescription Drugs in the United States In the United States, effective market exclusivity for a prescription drug is the time between US Food and Drug Administration (FDA) approval and the availability of the first generic version. Market exclusivity incorporates the minimum regulatory exclusivity periods granted to all FDA-apInvited Commentary page 637 proved drugs (eg, 5 years for new small-molecule drugs as set by the Hatch-Waxman Act of 1984), the remaining time on the original patent covering the active ingredient in the drug, the existence of so-called secondary patents covering peripheral aspects of drugs such as metabolites or alternative formulations,1 and other factors that affect generic entry, such as generic manufacturers’ prospects of profit-making in the market and legal settlements between manufacturers of brand-name and generic drugs regarding disputed patents. Recent research has shown that prescription brand-name drugs that eventually face generic competition have, on average, an effective market exclusivity period of 12.4 years.2 We assessed how the market exclusivity period varied among drugs for different therapeutic areas and for other characteristics of top-selling prescription medications.

Methods | This study was not submitted for institutional review board approval because it is based on publicly available data and involved no health records. We obtained annual published lists between 2000 and 2011 of the top 200 drugs by sales in the United States. We classified each agent into a primary therapeutic area. Using Medicaid prescription data compiled by the Centers for Medicare & Medicaid Services, we determined if a brand-name drug experienced generic competition from 2000 to 2012.3 We defined initiation of generic competition as the first quarter in which generic prescriptions were filled. For the subset of drugs that lost market exclusivity, we used the Drugs@FDA database4 to identify the approval date, chemical type (new molecular entity or new formulation), and whether the drug received a priority review. We determined whether the FDA granted each drug a special developmental designation (orphan drug, accelerated approval, or fast-track status).5 For all drugs that were new molecular entities and became generically available, we used a framework developed by the FDA to categorize their innovativeness and the size of the company that sponsored their FDA applications based on sales revenue.6 We performed Wilcoxon rank sum and Kruskal-Wallis tests to examine differences among our comparison groups of drugs. Results | Among the 437 top-selling drugs in our sample, 175 (40.0%) experienced generic competition by the end of 2012 (Figure). Only 7 of 50 therapeutic agents in endocrinology

Figure. Generic Availability of Top-Selling Prescription Drugs in the United States, 2000-2012 70

42% 57%

Generic 53%

Brand-name only

60 14%

Drugs, No.

50

40%

40

18%

30

42%

33%

42% 22%

20

63%

33%

Dermatology

Genitourinary

10

0

Infectious Disease

Neuropsychiatry Cardiovascular Disease

Endocrinology

Allergy and Pulmonology

Hematology and Oncology

Pharmaceutical agents ranked in the top 200 drugs by sales in the United States between 2000 and 2011, stratified by therapeutic area (N = 437). The light blue segment of each bar represents the number of agents in each therapeutic area that experienced competition by the end of 2012; the dark blue segment represents the number of agents available as brand-name drugs

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Analgesics

Gastroenterology Rheumatology

Othersa

only. The percentage above each bar represents the proportion of top-selling agents in each therapeutic area that experienced generic competition. a Includes imaging agents (n = 2), musculoskeletal drugs (n = 2), ophthalmologic drugs (n = 11), renal drugs (n = 2), transplantation medicine (n = 3), and vaccinations (n = 7).

(Reprinted) JAMA Internal Medicine April 2015 Volume 175, Number 4

Copyright 2015 American Medical Association. All rights reserved.

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Letters

Table. Effective Market Exclusivity Periods of Top-Selling Prescription Drugs That Experienced Generic Competition, 2000-2012 Pharmaceutical Agent Classification

No.

Effective Market Exclusivity, y, Median (IQR)

All agents

175

12.5 (8.5-14.8)

P Value

Chemical type New molecular entities

102

13.8 (10.8-14.8)

73

10.0 (6.9-13.9)

Dermatology

10

14.8 (9.0-16.3)

Cardiovascular disease

33

14.5 (11.5-15.0)

Infectious disease

28

14.4 (11.6-16.0)

New formulations

Variations in time of market exclusivity among top-selling prescription drugs in the United States.

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