Patent thicket asserted by Salix against Norwich in the rifaximin district court cases
Rifaximin illustrates the anticompetitive gamesmanship that patents with double patenting rejections and terminal disclaimers enable. When Norwich filed an Abbreviated New Drug Application (ANDA) to market generic rifaximin in 2020, Salix asserted a thicket with 26 patents including 19 that had terminal disclaimers. The court ordered Salix to narrow its contentions before trial and the company presented evidence of infringement for only seven of the 26 asserted patents. The case concluded in 2022 with the invalidation of four of the seven patents that reached trial, including two that claimed methods of treating irritable bowel syndrome (IBS). In 2023, the U.S. Patent and Trademark Office (USPTO) granted Salix two new terminally disclaimed patents claiming methods of treating IBS in females. Salix then asserted the newer IBS patents against Norwich in 2024, delaying generic competition for several more years while Americans pay among the highest prices in the world for rifaximin. Read the Generation Patient report on how patent thickets increase costs and delay access for young adult patients.
Patent numbers were compiled from the complaints filed by Salix against Norwich and verified against Orange Book listings. Filing dates and terminal disclaimer status were collected from USPTO records. Expiration dates are based on Orange Book entries. Patent scope descriptions are based on the claims as characterized in the complaints. Data current as of April 2026.