An ongoing dustup between Amgen and the FDA recently intensified when the agency accused the company of scoring a drug approval based on “manipulated” data.
The tension goes back to the 2021 approvals process for Tavneos, when an FDA advisory committee pointed to potential problems with the interpretability of the data. Tavneos was OK’d all the same that year and then got scooped up by Amgen in a $3.7 billion takeover of its original developer, ChemoCentryx.
But the FDA circled back on the drug, which was approved for a rare autoimmune condition, earlier this year, raising concerns about serious liver injuries and deaths among patients on Tavneos that have since been reported. Although the agency asked Amgen to yank the treatment from the market, the company dug its heels in, pointing out that most of the reported adverse events were in a narrow population — Japanese patients 65 and older.
Now, the back-and-forth is ramping up, with the FDA officially putting the wheels in motion to remove its approval.
Last week, the agency published a proposal to withdraw the drug from the market, arguing that back when it was in trials, “unblinded study personnel” tampered with the data. The FDA also said that Amgen did not disclose its original analysis of the clinical data, which violates federal regulations. Now, the agency “can no longer conclude that there is, or has ever been, a valid demonstration that Tavneos is effective for its approved use.”
While the FDA’s proposal did not include evidence to back up its allegations, the recent escalations follow the agency’s typical playbook for pulling a drug from circulation, said Ted Sullivan, a partner at the law firm Quarles.
“In this situation, there were significant adverse event reports along with allegations of significant irregularities or misconduct of the key clinical trials,” Sullivan said in an email. “It is not surprising that FDA has taken this action, and it is in line with what I would have expected.”
Amgen hasn’t given up on the drug yet though. In its first quarter earnings report, which was issued days after the agency’s withdrawal proposal, the company said it plans to “engage with the FDA” and that it believes Tavneos “demonstrates effectiveness and a favorable benefit-risk profile.” It also filed a proposed amendment to the drug’s existing warning label that would offer more information about its risks.
Amgen has plenty of reasons to hang on tight to Tavneos.
What’s at stake for Amgen and FDA
Sales for Tavneos, a first-in-class C5a receptor inhibitor cleared for two types of ANCA-associated vasculitis, have skyrocketed in recent years. Between 2023 and 2024, Tavneos sales grew by 111% and then soared another 62% last year, reaching $459 million globally.
The company also has ambitions to expand the drug’s reach. Pegged as a potential “pipeline in a pill,” Tavneos is being studied to treat several inflammatory diseases, Amgen said when it completed the ChemoCentryx deal in 2023.
Developing new top-selling drugs is particularly important to Amgen, which, like many Big Pharmas, is grappling with major patent cliffs.
Two of the company's blockbuster osteoporosis drugs — Prolia and Xgeva — began facing biosimilar competition last year. Amgen’s higher earner, Prolia, experienced just a 1% sales growth in 2025 while Xgeva’s worldwide sales dropped by 6%. Combined, they represented about $6.5 billion in sales in 2025, but biosimilar competition is ramping up more this year as new copycats win approval.
By 2028, Amgen will also begin losing patent protections for Repatha and Enbrel, two of its other best-selling drugs, which hauled in about $5.2 billion combined in global sales last year.
The FDA, meanwhile, also has a reputation to maintain as it widens its push to crack down on the industry.
Last year, for example, the agency implemented a policy to “promptly” publish complete response letters after they’re issued to pharma companies. In the past, the notices were typically only published by companies, if at all, giving the industry better control of the narrative around a drug’s rejection. But making the letters public will provide better context to shareholders, and it could restore public trust, the agency said.
The FDA also took the unusual step last year of including images of poor conditions inside a manufacturing facility with a Form 483 warning letter and has recently publicly and harshly called out biopharma leaders for allegedly making misleading marketing claims.
The agency’s showdown with Amgen over Tavneos marks another opportunity to demonstrate its eagerness to take action against pharma. So far, the agency appears to be moving as quickly as it can.
“The timeline for the current action seems about right, given what we know — FDA only discovered the clinical trial problems in the summer of 2025, and fairly quickly acted on this information to address the issues with Amgen,” Sullivan said. “There were also post-marketing data that suggested safety problems with the drug, but it can take some time for those to become apparent.”
In this regulatory environment, Amgen’s scuffle with FDA offers a key reminder to the industry, Sullivan said.
“Quite simply, don’t play games with your clinical trials data,” he said.
