Sales of the problematic Amgen Inc. drug Tavneos resumed late last week in Japan with a new warning label after several patient deaths potentially linked to the drug.

The drug’s future in the United States is still uncertain amid renewed regulatory scrutiny following revelations of alleged data manipulation in clinical trials for the drug several years ago.

Tavneos, which also goes by the generic name avacopan, was developed by San Carlos-based ChemoCentryx Inc. to treat several rare autoimmune diseases or conditions that cause inflammation in small blood vessels. That inflammation can sometimes be fatal. Tavneos is often prescribed in combination with other drugs.

Thousand Oaks-based Amgen bought ChemoCentryx in late 2022, nearly a year after the drug had been approved and had gone on the market. In its 2025 annual report, Amgen listed Tavneos sales at $459 million.

Patient deaths in Japan

Nagano, Japan-based Kissei Pharmacutical, which holds the license to sell Tavneos in that country, reported on May 15 that 20 people who were taking the drug had died from injuries to the liver. Kissei Pharmaceutical said that while a direct link to Tavneos had not been established in all the deaths, it was nonetheless recommending that all clinicians in Japan stop writing new prescriptions for it immediately.

Amgen issued a statement the same day noting that the 20 deaths were out of a total of roughly 8,500 patients taking the drug in Japan. The company also noted that there had been no fatalities in the U.S. from liver injuries among the more than 8,000 patients in this country who have taken the drug.

After meeting with Japan’s Ministry of Health last week, Kissei Pharmaceutical announced last week it was sending an emergency warning to all clinicians in Japan that use of the drug could lead to severe liver dysfunction, including vanishing of bile ducts that drain waste products from the liver. The same warning label would be placed on all future packaging. With those conditions in place, Kissei said health practitioners could resume prescribing the drug.

The Japanese Ministry of Health simultaneously advised that all doctors and other health practitioners carefully monitor any patients taking Tavneos. The agency recommended that patients already taking Tavneos shouldn’t on their own stop taking it but should instead consult with their physicians about the best course forward.

Amgen in its statement said similar warnings have long been on Tavneos drug packaging within the United States.

Trouble in the U.S.

Meanwhile, the future status of the drug in the U.S. is uncertain.

On April 27, the Center for Drug Evaluation and Research, a division of the U.S. Food and Drug Administration, sent a letter addressed to Nicole Cheung, Amgen’s manager of global regulatory affairs, stating that the division is proposing to withdraw approval of the new drug application for Tavneos that the FDA had granted in 2021.

In its letter, the Center for Drug Evaluation and Research detailed allegations that had recently come to light that endpoint results for a Phase 3 clinical trial conducted in 2019 for ChemoCentryx’ drug were manipulated to make the drug appear effective “when the original analysis did not support that conclusion.”

The letter maintains that if the original results had been submitted instead of the manipulated results, the drug would not have been determined to be effective.

The letter also noted that liver toxicity was identified as a key safety risk in the original material reviewed by the FDA back in 2021.

Amgen has two options in response to the approval withdrawal notice: On its own pull the drug from the market or request a hearing with the Center for Drug Evaluation and Research. If Amgen chooses the hearing route, it has until June 1 to submit its hearing request and until June 29 to submit all data in support of that request.

In its May 15 statement, Amgen indicated it “continues to engage with the FDA regarding Tavneos.”

Meanwhile, Tavneos is also under review by the European Medicines Agency, the main drug regulating authority for the European Union with its 27 member nations.