Merck has received FDA approval for an expanded indication of its activin signaling inhibitor WINREVAIR (sotatercept‑csrk) for adults with WHO Group 1 pulmonary arterial hypertension (PAH). The approval extends the drug’s use to patients with WHO functional class III or IV PAH, a population that remains at high risk for clinical worsening, hospitalization, lung transplantation, and death.
The approval is based on the Phase 3 ZENITH trial, which enrolled 172 adults (86 in the WINREVAIR group and 86 in the placebo group). The composite primary endpoint—time to first occurrence of all‑cause death, lung transplantation, or PAH‑worsening hospitalization of ≥24 hours—occurred in 15 (17 %) WINREVAIR‑treated participants versus 47 (55 %) placebo‑treated participants, yielding a 76 % relative risk reduction. The study also demonstrated significant improvements in 6‑minute walk distance and WHO functional class, and was stopped early for overwhelming efficacy.
WINREVAIR is administered as a weight‑based subcutaneous injection, starting at 0.3 mg/kg and titrated to a target of 0.7 mg/kg every three weeks. Common adverse reactions observed in the trial included infections, epistaxis, diarrhea, and telangiectasia. The drug can raise hemoglobin levels, potentially leading to erythrocytosis, and lower platelet counts, increasing bleeding risk, and requires routine monitoring. WINREVAIR is a recombinant activin receptor type IIA‑Fc fusion protein and represents a novel fourth therapeutic pathway for PAH, distinct from the nitric oxide, endothelin, and prostacyclin pathways.
Merck first received FDA approval for WINREVAIR in March 2024 based on the STELLAR study, which showed improvements in exercise capacity and WHO functional class. The expanded indication broadens the drug’s commercial portfolio and provides Merck with a new revenue stream in the PAH market, a niche with limited treatment options. The approval also reinforces Merck’s biologics platform and complements its flagship oncology product Keytruda. WINREVAIR is licensed to Bristol Myers Squibb, further supporting its development and commercialization.
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