Merck, known as MSD outside the United States and Canada, announced that the US Food and Drug Administration (FDA) has approved an update to the US product label for Winrevair (sotatercept-csrk) based on findings from the Phase 3 HYPERION trial. The updated label includes efficacy and safety data from adults newly diagnosed with pulmonary arterial hypertension (PAH, WHO Group 1 pulmonary hypertension) who were within 12 months of diagnosis and had WHO functional class II or III disease with intermediate to high risk of progression. 

Winrevair is an activin signalling inhibitor approved in the US for the treatment of adults with PAH to improve exercise capacity and WHO functional class and reduce the risk of clinical worsening events, including PAH-related hospitalisation, lung transplantation and death. The latest label update provides additional information on its use when added to background PAH therapy during the first year following diagnosis. 

The HYPERION trial enrolled 320 participants, with 160 receiving Winrevair and 160 receiving placebo, alongside background therapy. The addition of Winrevair reduced the risk of clinical worsening events by 76 percent compared with placebo, with a hazard ratio of 0.24. A first clinical worsening event occurred in 10.6 percent of participants receiving Winrevair compared with 36.9 percent of those receiving placebo. 

The primary composite endpoint assessed the time to death or the first confirmed morbidity event. Events included all-cause death, unplanned PAH-related hospitalisation lasting at least 24 hours, atrial septostomy, lung transplantation, or a reduction in six-minute walk distance combined with worsening of WHO functional class, signs or symptoms of increased right-heart failure, or the addition or modification of background PAH therapy. 

Participants had been diagnosed with PAH for an average of 7.2 months. At baseline, 72 percent were receiving double background therapy and 28 percent were receiving triple therapy, while 17 percent were receiving prostacyclin infusion therapy. The treatment effect was consistent across the prespecified subgroups reported by the company. 

The treatment can also increase haemoglobin levels and potentially cause erythrocytosis, which, when severe, may increase the risk of thromboembolic events or hyperviscosity syndrome. Winrevair may decrease platelet counts and cause severe thrombocytopenia, which can increase the risk of bleeding. The FDA-approved safety information calls for monitoring haemoglobin and platelet counts before each dose during the first five doses, or longer if values remain unstable, and periodically thereafter. Treatment should not be initiated when platelet counts are below 50,000/mm³. 

Earlier in September 2026, the European Respiratory Society published updated clinical guidelines for PAH that included Winrevair. According to Merck, the guidelines provide a strong recommendation for use of Winrevair in adults with PAH receiving background therapy who have not achieved low-risk status at follow-up. 

The US FDA's September 2026 action follows its earlier 2025 label update for Winrevair based on the Phase 3 ZENITH study.