CHMP Rejects Omeros’ Narsoplimab for Second Time

The European Medicines Agency's Committee for Medicinal Products for Human Use (CHMP) confirmed on 16 October 2026, after re-examination, its negative opinion on Omeros Corporation's marketing authorisation application for narsoplimab (Yartemlea) in transplant-associated thrombotic microangiopathy (TA-TMA), a rare and often-fatal complication of stem cell transplantation. It is the second time the committee has rejected the filing. In response, Omeros says it will end the European compassionate-use program that had been the only route to the drug for EU patients — even as narsoplimab remains FDA-approved and commercially sold in the United States.

A second rejection, not a first look

CHMP's original negative opinion on narsoplimab for TA-TMA was adopted in June 2026. Omeros exercised its right to request re-examination — a formal EU procedure that triggers review by an ad hoc group of independent experts separate from the committee members who issued the first opinion. That group, eight members in this case, examined the case and, according to Omeros' account of the re-examination minutes, recommended that external experts review the trial's individual patient-level data before the committee finalized its view. Omeros says it submitted that patient-level data to CHMP in August, ahead of the re-examination's conclusion. Its own telling is that the committee did not pass that data on to the expert group it had convened — a procedural detail Omeros is treating as central to its disagreement with the outcome, though the company's announcement does not include CHMP's own account of why the data was not forwarded or whether the committee judged it unnecessary to its determination.

What the evidence looked like

TA-TMA is a complication of hematopoietic stem cell transplantation involving small-vessel blood clots that damage organs, with mortality rates in some published series exceeding 80 percent for severe, treatment-refractory cases — the population narsoplimab targets. Narsoplimab is a monoclonal antibody that inhibits MASP-2, a protease in the lectin pathway of the complement system implicated in the vascular injury TA-TMA causes. The pivotal trial behind both the US approval and the EU filing was a single-arm study of roughly 28 patients, without a randomized control arm; its survival claim rested on comparison to an external, historical control population rather than a contemporaneous comparator group. That design choice is a recurring sticking point in ultra-rare-disease drug development, where enrolling a large randomized trial is often impractical — FDA accepted the external-control comparison as adequate for approval in December 2025; CHMP, across two opinions now, has not. Trade coverage also cites a safety figure from the trial — serious or life-threatening infections in 36 percent of patients — as a factor in CHMP's calculus, consistent with narsoplimab's mechanism of suppressing part of the complement immune pathway.

The access consequence

The rejection itself was, by CHMP precedent, not guaranteed to end EU access outright: Omeros had been supplying narsoplimab to European TA-TMA patients through a compassionate-use program while the marketing authorisation application was pending. That changes now. Citing commercial demand from the drug's established US market under its Yartemlea approval, Omeros has told CHMP it intends to wind the European program down — patients currently on therapy will receive enough drug to complete their ongoing course, but the company will not enroll new EU patients through that pathway going forward. For a disease this acute and this lethal, the practical effect of a second CHMP rejection is not merely that no new EU patients can access narsoplimab through a licensed product; it is that the one remaining access route, compassionate use, is also closing. CEO Gregory Demopulos characterized the outcome as a setback the company does not accept quietly: Omeros said in its own announcement that it is “deeply disappointed in the re-examination process and outcome.”

Frequently asked questions

What did CHMP decide on 16 October 2026?

The Committee for Medicinal Products for Human Use confirmed, after re-examination, its negative opinion on Omeros' marketing authorisation application for narsoplimab (Yartemlea) in transplant-associated thrombotic microangiopathy (TA-TMA) — a rare, often-fatal complication of stem cell transplantation. It is the second time CHMP has rejected the application for this use; the original negative opinion was adopted in June 2026.

Why did CHMP reject it?

Per Omeros' own account and trade coverage, CHMP's concerns centered on the pivotal study's design: a single-arm trial of roughly 28 patients, with no randomized control group, relying on an external-control comparison for its survival claim that the committee judged insufficient to establish efficacy. Coverage also cites a safety signal — serious or life-threatening infections reported in 36% of trial patients. Omeros has not published CHMP's full assessment report.

What happened during the re-examination?

Omeros requested re-examination of the original opinion, triggering review by an eight-member ad hoc expert group (AHEG). Omeros says it submitted substantial patient-level data in August in support of its case, and that the AHEG itself recommended external review of that data — but that CHMP did not provide the patient-level data to the expert group before the panel's review concluded.

What happens to patients who were already accessing the drug?

Narsoplimab was approved by the FDA as Yartemlea in December 2025 and remains commercially available in the US. With the EU authorisation rejected a second time and citing rising US commercial demand, Omeros has told CHMP it intends to end its European compassionate-use program. Patients already enrolled will receive enough drug to complete their current course; no new EU patients will be able to start the drug through that pathway.