Omeros Shares Slide Following European Regulatory Setback for Narsoplimab

3-line summary

• The European Medicines Agency's CHMP maintained a negative opinion on narsoplimab after re-examination, declining to approve it for transplant-associated thrombotic microangiopathy (TA-TMA) following stem-cell transplant — reaffirming its initial negative stance from June 2026. An 8-member expert group convened by CHMP had recommended that individual patient-level data be reviewed by outside experts, but per the report, CHMP did not provide that data to the expert group before its decision; Omeros had submitted substantial patient data in August.
• Omeros shares fell about 4% in Friday morning trading. In response, Omeros told CHMP it will end its European compassionate-use program for the drug, citing surging US demand; European patients currently on the program will receive enough supply to complete their treatment course. The company plans to start trials for acute respiratory distress syndrome (ARDS) and prevention of high-risk pediatric TA-TMA later this year.
• Narsoplimab targets MASP-2, an enzyme in the lectin pathway of the complement system. The FDA approved it in December 2025 under the brand name Yartemlea, the first FDA-approved treatment for TA-TMA in patients age 2 and older — a contrast the article drew with the EU rejection. The article noted it is the only marketed systemic complement inhibitor without a boxed warning, REMS, or specific vaccination requirements, and cited rising US demand as the direct reason for ending the European program.

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