— Initial Orders Received and Fulfilled from Multiple Transplant Centers, with YARTEMLEA Now Administered to Both Adult and Pediatric Patients with TA-TMA —

Omeros Corporation (NASDAQ: OMER) today announced that the first commercial shipments of YARTEMLEA^® (narsoplimab-wuug) to its distributors were completed last week, with orders from transplant centers beginning that same day. Both adult and pediatric patients with stem cell transplant-associated thrombotic microangiopathy (TA-TMA) are now receiving YARTEMLEA, including patients who have recently failed prior off-label C5-inhibitor regimens, in both hospital and outpatient settings.

YARTEMLEA is the first and only approved therapy for TA-TMA, an often-fatal complication of stem cell transplantation driven by activation of the lectin pathway of complement. YARTEMLEA, which was approved by the U.S. FDA on December 23, 2025, selectively inhibits MASP-2, the effector enzyme of the lectin pathway, blocking the pathway’s activation while preserving classical and alternative complement functions important for host defense against infection. YARTEMLEA is approved for use in adults and in children ages two years and older.

TA-TMA can occur following both autologous and allogeneic hematopoietic stem cell transplantation, with substantially higher prevalence following allogeneic transplant. Approximately 30,000 allogeneic transplants are performed annually in the United States and Europe. Recent studies estimate that TA-TMA develops in up to 56 percent of allogeneic transplant recipients, though the condition is thought to be frequently under-recognized, and timely diagnosis can be a key factor in outcomes.

A marketing authorization application for YARTEMLEA for the treatment of TA-TMA is currently under review by the European Medicines Agency with a decision expected in mid-2026.

About Omeros Corporation

Omeros is an innovative biotechnology company that discovers, develops, and commercializes first-in-class small-molecule and protein therapeutics for large-market and orphan indications, with particular emphasis on complement-mediated diseases, cancers, and addictive or compulsive disorders. Omeros’ lead lectin pathway inhibitor YARTEMLEA^® (narsoplimab-wuug), which inhibits the pathway’s effector enzyme MASP-2, is FDA-approved and commercially available in the U.S. for the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA) in adult and pediatric patients ages two years and older. A marketing authorization application for YARTEMLEA in TA-TMA is currently under review by the European Medicines Agency. OMS1029, Omeros’ long-acting MASP-2 inhibitor, has successfully completed Phase 1 clinical trials.

Under a recently announced asset purchase and licensing agreement, Novo Nordisk acquired global rights to zaltenibart (formerly OMS906), a MASP-3 inhibitor in clinical development for PNH and other alternative pathway indications, along with associated intellectual property and related assets. Omeros’ pipeline also includes OMS527, a phosphodiesterase 7 inhibitor in clinical development for cocaine use disorder and fully funded by the National Institute on Drug Abuse, as well as a growing portfolio of novel molecular and cellular oncology programs. For more information about Omeros and its programs, visit www.omeros.com.

About YARTEMLEA^®

YARTEMLEA^® (narsoplimab-wuug), is the first and only approved inhibitor of the lectin pathway of complement. YARTEMLEA, a fully human monoclonal antibody, inhibits mannan-binding lectin-associated serine protease-2 (MASP-2), the effector enzyme of the lectin pathway. In hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), MASP-2 inhibition prevents lectin pathway-mediated cellular injury, including endothelial damage in small blood vessels, and thrombus formation. By selectively blocking activation of the lectin pathway, YARTEMLEA preserves classical and alternative pathway activity, including functions essential to the adaptive immune response.

YARTEMLEA is approved by the U.S. FDA for the treatment of TA-TMA in adults and in children ages two years and older. A marketing authorization application for YARTEMLEA for TA-TMA is under review by the European Medicines Agency (EMA).

YARTEMLEA has received breakthrough therapy and orphan drug designations from the FDA for TA-TMA, and the EMA has granted it orphan drug designation in hematopoietic stem-cell transplantation.

Important Safety Information for YARTEMLEA^®

Contraindications

None.

Warnings and Precautions

Serious and life-threatening infections have occurred in patients treated with YARTEMLEA.

• In clinical trials in patients with TA-TMA, serious infections (regardless of causality) were reported in 36% (10/28) of patients receiving YARTEMLEA. Reported serious infections included sepsis, viral infections, pneumonia, bacteremia, fungal infection, gastroenteritis, respiratory tract infection, and urosepsis.
• If YARTEMLEA is administered to patients with active infections, monitor closely for worsening infection and treat promptly.

Adverse Reactions

The most common adverse reactions (≥20%), regardless of causality or relatedness to YARTEMLEA, were viral infections, sepsis, hemorrhage, diarrhea, vomiting, nausea, neutropenia, pyrexia, fatigue, and hypokalemia.

To report suspected adverse reactions, contact Omeros Corporation at 1-844-YARTEM1 (1-844-927-8361), or contact FDA at 1-800-FDA-1088 or through FDA MedWatch.

Please see Full Prescribing Information for YARTEMLEA.

About Hematopoietic Stem Cell Transplant-Associated Thrombotic Microangiopathy

Hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA) is a severe and often-fatal complication of hematopoietic stem cell transplantation in adults and children. TA-TMA is driven by systemic endothelial injury triggered by conditioning regimens, immunosuppressants, infection, graft-versus-host disease, and other transplant-related factors, with activation of the lectin pathway of complement playing a central role in disease pathogenesis.

TA-TMA can occur following both autologous and allogeneic transplant, with higher prevalence after allogeneic procedures. Approximately 30,000 allogeneic transplants are performed annually in the U.S. and Europe. Recent studies estimate that TA-TMA develops in up to 56 percent of allogeneic transplant recipients. Mortality in severe TA-TMA can exceed 90 percent, and survivors frequently face long-term renal complications, including dialysis dependence.

YARTEMLEA^® is the only approved treatment for TA-TMA.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, which are subject to the “safe harbor” created by those sections for such statements. All statements other than statements of historical fact are forward-looking statements, which are often indicated by terms such as “anticipate,” “believe,” “could,” “estimate,” “expect,” “goal,” “intend,” “likely,” “look forward to,” “may,” “objective,” “plan,” “potential,” “predict,” “project,” “should,” “slate,” “target,” “will,” “would,” and similar expressions and variations thereof. Forward-looking statements, including statements regarding the marketing authorization application for YARTEMLEA^® in Europe, prospects for obtaining EMA approval of YARTEMLEA in any indication, plans and expectations regarding the commercial launch of YARTEMLEA in the U.S., and in the EU following any EMA approval, our ability to consummate licensing, partnering or other transactions and the benefits, if any, we would receive from any such transactions, expectations regarding the sufficiency and availability of our capital resources to fund current and planned operations, including the commercialization of YARTEMLEA are based on management’s beliefs and assumptions and on information available to management only as of the date of this press release. Omeros’ actual results could differ materially from those anticipated in these forward-looking statements for many reasons, including, without limitation, unfavorable or unexpected regulatory conclusions or interpretations related to the clinical data, external registry data, statistical analyses or other information and data included in the YARTEMLEA MAA, inability to respond satisfactorily to information requests during regulatory review of the YARTEMLEA MAA, potential differences between the diagnostic criteria used in our pivotal trial and in the external registry, and whether the EMA determines the registry used in our statistical analysis is sufficiently representative of TA-TMA patients, unanticipated or unexpected outcomes or requirements of regulatory processes in relevant jurisdictions, our financial condition and results of operations, including our ability to raise additional capital for our operations or complete other transactions on favorable terms or at all, regulatory processes and oversight, challenges associated with manufacture or supply of our products to support clinical trials, regulatory inspections and/or commercial sale following any marketing approval, changes in reimbursement and payment policies by government and commercial payers or the application of such policies, intellectual property claims, competitive developments, litigation, and the risks, uncertainties, and other factors described under the heading “Risk Factors” in our Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 31, 2025 and in subsequently filed Quarterly Reports on Form 10-Q. Given these risks, uncertainties, and other factors, you should not place undue reliance on these forward-looking statements, and we assume no obligation to update these forward-looking statements, whether because of new information, future events or otherwise, except as required by applicable law.

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