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New trial data offer a cautious vote of confidence for avacopan, the embattled vasculitis drug fighting to stay on the U.S. market. The AvacoStar interim results show liver abnormalities were four times more common with avacopan than with standard alternatives — but were rare and mostly resolved. The findings could help Amgen push back against the FDA's voluntary withdrawal request.
Avacopan (Tavneos), the complement-targeting drug for antineutrophil cytoplasmic antibody-associated vasculitis (AAV), has had a rough 2026 — but new safety data may give it a fighting chance in the U.S. Interim results from the AvacoStar trial, presented at the American College of Rheumatology annual meeting, found that while avacopan was linked to a fourfold higher rate of liver abnormalities compared to rituximab or cyclophosphamide, those events were uncommon, mostly mild, and nearly all resolved. Serious infections, cardiac events, and malignancies occurred at similar rates across both groups.
The drug's troubles stem from a data integrity scandal: its original developer, ChemoCentryx, had pivotal trial results "readjudicated" after unblinding — shifting the outcome from a missed endpoint to a met one. That revelation prompted the FDA to request voluntary market withdrawal, and regulators in the EU and U.K. have already pulled the drug. Amgen, which acquired ChemoCentryx in 2022, has refused the FDA's request, and the agency hasn't made it mandatory.
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Why it matters: With the EU and U.K. already pulling avacopan, the U.S. is the last major market where it remains available. These interim safety findings — combined with a recent Italian efficacy study — could be pivotal in determining whether avacopan survives as a treatment option for AAV patients who have limited alternatives.
