Amgen (Nasdaq: AMGN) is facing intensifying regulatory and safety pressure over Tavneos (avacopan) in Japan after partner Kissei Pharmaceutical (Tokyo: 4547) issued a safety notice guiding doctors to cease from making new prescriptions for the drug and assess ongoing treatments. As per a report from the Wall Street Journal, the drug has allegedly been linked to around 22 deaths due to serious liver dysfunction, prompting a halt to new prescriptions and a review of ongoing treatment.
Kissei said most severe liver injury cases occurred within three months of treatment initiation, and that some deaths were associated with a severe liver condition that destroys bile ducts, though a direct causal link to Tavneos had not been confirmed in all cases. The company said approximately 8,503 patients in Japan had received the drug since its launch there in 2022, and it urged regular liver function monitoring and prompt discontinuation if abnormalities were detected.
The safety notice does not constitute a formal market withdrawal in Japan, but Kissei’s request that physicians stop initiating new prescriptions represents a material restriction on the drug’s use. The episode compounds existing regulatory pressure in the US, where the FDA had already identified dozens of liver injury cases globally — many of them in Japan — and moved to formally begin withdrawal proceedings after Amgen declined a request to voluntarily pull the drug from the US market earlier in 2026.
Tavneos and its mechanism
Tavneos is a selective oral small molecule antagonist of the complement 5a receptor (C5aR1), a G protein-coupled receptor that binds the pro-inflammatory complement fragment C5a. By blocking this interaction, the drug inhibits complement-mediated neutrophil activation and downstream tissue inflammation. It is approved as an adjunctive treatment for adult patients with severe active anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis, including granulomatosis with polyangiitis and microscopic polyangiitis, used in combination with standard therapy including glucocorticoids.
ANCA-associated vasculitis is a group of rare autoimmune diseases causing inflammation in small- to medium-sized blood vessels. The condition carries substantial morbidity, and Tavneos represented the first novel mechanistic approval in this indication in decades when the FDA cleared it in October 2021.