Serial patent litigation: an emerging strategy to delay entry of generic competition.

The Hatch-Waxman Act of 1984 was designed to accelerate generic drug entry by establishing a framework for resolving patent disputes between brand-name and generic manufacturers. While the Act has facilitated competition and expanded the availability of affordable medicines, brand-name firms have increasingly exploited its procedural structure to delay or deter generic competition through "serial litigation." This strategy involves filing successive, questionable lawsuits, often based on non-innovative continuation patents. Even if the brand ultimately loses, the delays and litigation costs can discourage generic firms from entering the market or compel them to settle on terms that undermine patients' timely access to affordable generics. In the case of Astellas's overactive bladder drug mirabegron (Myrbetriq), after an initial Hatch-Waxman case settled in 2020 with generic entry expected in 2024, Astellas pursued 4 additional lawsuits, each built on new but substantively indistinguishable patents. These tactics have delayed broad competition, leaving only 2 firms to launch in 2024 under the threat of massive damages. Similar patterns are observed with other drugs, including bimatoprost (Latisse), aflibercept (Eylea), and tasimelteon (Hetlioz).