Amgen's Tavneos Withdrawal Fight Intensifies Over FDA Data Manipulation Letter and Japanese Safety Signal
The high-stakes regulatory battle over the future of Amgen's oral complement C5a receptor inhibitor, Tavneos (avacopan), has escalated dramatically following a June 25, 2026, Bloomberg investigation revealing specific FDA allegations of data manipulation, alongside a severe post-marketing safety signal in Japan.
Amgen acquired Tavneos through its $3.7 billion acquisition of ChemoCentryx in 2022. The drug generated $459 million in 2025 and is projected by analysts to reach $527 million in 2026. However, its commercial future is now in severe jeopardy as the FDA's Center for Drug Evaluation and Research (CDER) pursues a formal proposal to withdraw its approval.1
FDA Data Manipulation Allegations Revealed
According to a newly disclosed letter from the FDA, the agency's effort to pull Tavneos from the market centers on allegations of clinical trial fraud.2 The FDA alleges that personnel at ChemoCentryx, the drug's original developer, "manipulated" the pivotal study data used to secure FDA approval in 2021 to make the pill look safer and more effective than it actually was.
"According to a letter from the U.S. FDA, ChemoCentryx personnel “manipulated” study data to make Tavneos, a pill made to treat a rare blood vessel disorder, look safer and more effective."
Amgen is actively contesting the withdrawal proposal and has enlisted the Duke Clinical Research Institute (DCRI) to conduct an independent re-evaluation of the pivotal ADVOCATE trial data, which it plans to submit before the FDA's public docket closes on June 29, 2026.
Post-Marketing Safety Signal in Japan
Compounding the regulatory pressure, Tavneos has come under intense safety scrutiny in Japan. Kissei Pharmaceutical, Amgen's partner in Japan, issued urgent warnings following reports of 20 patient deaths and 22 cases of drug-induced liver injury (DILI) associated with the drug.
In response, the European Medicines Agency (EMA) has also strengthened liver monitoring requirements for Tavneos, advising clinicians to perform frequent liver function tests and immediately discontinue the drug if liver injury is suspected. Amgen has updated its prescriber guidance in the U.S. to address these hepatotoxicity risks, though no deaths have been reported domestically to date.
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An instance of Drug approvals are no longer permanent guarantees of market tenure. — An approved drug's market tenure is actively threatened as the FDA attempts to revoke its green light after discovering clinical trial errors. ↩︎
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An instance of Data integrity failures trigger a global regulatory crackdown on clinical trial validity. — Federal regulators aggressively pursued the withdrawal of an approved therapeutic once allegations of clinical trial data manipulation surfaced. ↩︎