Delisted Patents on Pharmaceuticals, 1998-2024.

Patents listed in the US Food and Drug Administration's (FDA) Orange Book can delay generic competition, yet little is known about how often patents are removed before expiration or why these delistings occur. We reviewed Orange Book records from 1998 through 2024 to identify patents removed before their expiration dates, classified patents according to the subject matter of their claims and assessed potential reasons for delisting using patent litigation and prosecution databases, FDA records, and Federal Trade Commission (FTC) actions. Among 9,980 patents listed during the study period, 535 (5%) were delisted before expiration. Only 71 (13%) claimed active ingredients; most delisted patents instead covered methods of use (177, 38%), formulations (167, 36%), or delivery devices (75, 16%). Potential reasons for delisting included potential invalidation in litigation (226, 42%), product discontinuation (207, 39%), and patent reexamination or reissue (60,11%). Orange Book patent delistings predominantly involved secondary patents rather than active-ingredient patents. Greater clarity and oversight regarding Orange Book listing requirements could reduce questionable listings and unnecessary barriers to generic competition.