FDA Delays Decision on Omeros' Transplant Drug Narsoplimab

The U.S. Food and Drug Administration (FDA) has extended its review period for Omeros Corporation's narsoplimab, pushing back the decision date by three months. This delay marks another setback for the biotech company in its efforts to bring the transplant-associated thrombotic microangiopathy (TA-TMA) treatment to market.

Extended Review Period and Labeling Discussions

Omeros announced that the FDA has moved the decision date for narsoplimab from September 25 to December 26, 2025. The agency cited the need to review additional information provided by the company in response to its queries. Despite the delay, the FDA has indicated that, barring any major deficiencies, labeling discussions are expected to commence no later than October 2025.

The company remains optimistic, stating that all analyses requested by the FDA have consistently demonstrated statistically significant support for narsoplimab's benefits, as outlined in the Biologics License Application (BLA) resubmission.

Narsoplimab's Journey and Clinical Data

Narsoplimab, an anti-MASP-2 antibody, aims to treat TA-TMA, a potentially life-threatening complication of hematopoietic stem cell transplants. The drug's path to approval has been fraught with challenges, including an initial FDA rejection in 2021.

Omeros' latest application is based on a new data analysis showing a 68% improvement in overall survival among patients treated with narsoplimab. This analysis compared 28 patients from the pivotal phase 2 trial to over 100 TA-TMA patients from an external control registry who did not receive the drug.

Strategic Focus and Future Outlook

As Omeros concentrates its efforts on narsoplimab, the company has temporarily halted clinical progress on two other assets: zaltenibart, a MASP-3 inhibitor ready for phase 3 trials in paroxysmal nocturnal hemoglobinuria, and OMS1029, a long-acting MASP-2 inhibitor prepared for phase 2 studies.

Gregory Demopulos, M.D., CEO of Omeros, expressed confidence in the company's trajectory, citing ongoing partnering discussions and potential value-driving milestones anticipated throughout the remainder of 2025 and into 2026. The company continues to prepare for the anticipated approval and subsequent launch of narsoplimab in TA-TMA, an indication with a growing unmet need and no currently approved treatments.