TL;DR
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Interim results from the ongoing AvacoStar study found that liver abnormalities occurred at a higher rate among patients taking avacopan than among those receiving rituximab or cyclophosphamide, but the absolute rate was low. The study reported no higher rates of serious infection, cardiac events or malignancies with avacopan; longer follow-up and the study’s nonrandomized treatment choices limit what can be concluded.
Interim results from a dedicated safety study found that avacopan was associated with more liver abnormalities than rituximab or cyclophosphamide in patients with antineutrophil cytoplasmic antibody-associated vasculitis, but the events were uncommon and generally resolved. Presented by Bernhard Hellmich of the University of Tübingen at the American College of Rheumatology’s annual meeting, the findings add to evidence relevant to the drug’s uncertain future in the United States.
The ongoing AvacoStar study enrolled 504 patients with highly active vasculitis in Britain and Germany. Clinicians selected treatment: 254 patients received avacopan and 250 received an alternative regimen based on rituximab or cyclophosphamide. The interim analysis used medical-record data available through September 2025. More than 95% of participants were still taking their original therapy at that cutoff.
Liver injury was the only one of four prespecified types of medical events of special interest that occurred at a significantly higher rate with avacopan. The reported incidence-rate ratio was 4.03 (95% confidence interval 1.55 to 10.48), while the absolute rate was 0.07 events per patient-year. The other monitored categories were serious infections, cardiovascular events and malignancies.
Serious infections occurred at 0.14 per patient-year in the avacopan group and 0.18 with the alternative treatments. Cardiac events were reported at 0.09 per patient-year in both groups, and malignancies at 0.02 per patient-year in each. Hellmich said there were 22 liver events overall; clinicians considered 10 probably or definitely unrelated to avacopan. Of the remaining 12, some patients continued treatment and others paused it. Twenty events had resolved by the analysis cutoff, and one more was later reported resolved.
Safety Evidence Amid U.S. Review
The findings provide a more focused comparison of adverse events in people receiving avacopan and conventional treatment, but they do not settle the broader questions around the drug. Avacopan’s U.S. availability is under pressure after concerns about its pivotal trial and reports of liver injury. A dedicated safety study can inform that debate, particularly because liver abnormalities remained more frequent with avacopan even though the absolute rate was low.
The results also put that risk alongside events seen with the alternatives: serious infections were reported in both groups, and the interim rates of cardiac events and malignancies were equal. These figures may help clinicians and regulators weigh potential risks, but the study was not randomized and does not establish that avacopan is safer or more effective overall. It is interim safety evidence, not a final verdict on the medicine.
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How Avacopan Reached This Point
Avacopan, marketed as Tavneos, was approved in the United States in 2021 for ANCA-associated vasculitis. It targets the complement pathway and was introduced as another treatment option alongside approaches including corticosteroids, rituximab and cyclophosphamide. The drug’s known liver risks were addressed with a warning on its label.
In 2026, scrutiny intensified after concerns emerged that results from the original pivotal trial had been readjudicated after the trial was unblinded, changing some patients’ classifications and affecting whether the primary endpoint was met. The FDA asked Amgen, which acquired the U.S. rights through its purchase of ChemoCentryx, to voluntarily withdraw the drug. The source report said Amgen had rejected that request and that the FDA had not made withdrawal mandatory. European regulators revoked the drug’s EU marketing authorization in August, while its U.K. withdrawal was scheduled for completion by March 2027.
AvacoStar began in 2023 under Vifor Fresenius Medical Care Renal Pharma, which had licensed avacopan in Europe and commissioned the dedicated safety study. The interim analysis covered an average of 16.2 months of avacopan treatment and 12.7 months with alternatives. Participants had a mean age of about 64; nearly three-quarters were newly diagnosed, and about half had serious kidney impairment.
““Residual bias” is a possibility.”
— Bernhard Hellmich, University of Tübingen
Limits of the Interim Findings
The reported results are not final: AvacoStar is ongoing, with completion scheduled for 2030. Longer follow-up could reveal risks that were not evident in the data available through September 2025. The study also relied on treatment choices made by clinicians, so differences between the groups may reflect patient or physician factors as well as the medicines.
The analysis does not determine whether avacopan caused every liver event. Treating clinicians judged 10 of the 22 events probably or definitely unrelated, while 12 were considered possibly, probably or certainly related. The interim report also cannot resolve the regulatory questions tied to the pivotal-trial readjudication. The FDA’s next action, and whether Amgen will change its position on a voluntary U.S. withdrawal, were not established in the report.
Longer Follow-Up and FDA Decisions
AvacoStar is expected to continue collecting safety information until its planned completion in 2030. Further results could clarify whether the low absolute rate of liver injury persists over longer treatment and whether other event rates change with time.
In the nearer term, the U.S. status of avacopan remains subject to the FDA’s response to concerns about the pivotal trial and liver-injury reports. The interim study findings may inform that assessment, but they do not themselves change the drug’s approval or establish what regulators will decide. The next milestones are additional trial data and any formal regulatory announcement.
Key Questions
What did the AvacoStar interim analysis find?
It found a higher rate of liver abnormalities with avacopan than with rituximab or cyclophosphamide, while the absolute rate was low. Interim rates of serious infections, cardiac events and malignancies were not higher with avacopan.
How many patients were included?
The study enrolled 504 patients in Britain and Germany: 254 received avacopan and 250 received an alternative treatment. Clinicians chose each patient’s treatment rather than assigning it randomly.
Does the study prove avacopan is safe?
No. The findings provide interim safety information but do not prove the drug is safe or establish that it caused every reported liver event. The study is ongoing, and its treatment-selection design may leave residual bias.
Is avacopan being withdrawn in the United States?
The source report said the FDA had asked Amgen to withdraw the drug voluntarily, but the request had not been made mandatory and Amgen had rejected it. The interim study results do not determine the FDA’s next decision.
Source: medpagetoday.com
