FDA rejects Omeros transplant drug over difficulties estimating its effect

There will be no miraculous escape for Omeros. Weeks after the FDA flagged deficiencies with the filing for approval of a stem cell transplant drug, the agency has issued the complete response letter (CRL) foreshadowed by its earlier communication. 

At the start of the month, Omeros revealed the FDA had found deficiencies in its filing for approval of narsoplimab in the treatment of a transplant complication. The discovery of issues that stopped the FDA from discussing labeling and postmarketing looked set to lead to a CRL, with Omeros having less than three weeks to resolve the problems. Sure enough, the FDA hit Omeros with a CRL.

In disclosing the setback, Omeros shared additional information about the FDA’s problems with the filing. According to Omeros, the FDA “expressed difficulty in estimating the treatment effect of narsoplimab” and said “additional information will be needed to support regulatory approval.” The only good news for Omeros is the FDA raised no barriers to approval related to manufacturing, safety or nonclinical issues.

The big outstanding question is what it will take to satisfy the FDA’s demand for more information. Omeros said it remains confident in its efficacy and safety data, adding that it worked with the FDA on the clinical development plan. The agency clearly remains unconvinced, though.

RELATED: Omeros hits endpoint in pivotal stem cell transplant study

Omeros sought approval on the strength of a 28-participant single-arm, open-label clinical trial. After originally refusing to disclose key information such as the number of subjects in the study, Omeros released final data from the trial last year. Sixty-one percent of patients had complete responses, as defined by the presence of improvements in disease markers and organ function.

Shares in Omeros climbed in the weeks and months after the release of the full data but were sent spiraling downward by news of deficiencies identified by the FDA. Despite the FDA telegraphing its intentions to issue a CRL, shares in Omeros still fell further in response to the news, sliding 15% in premarket trading to $6.60.