The FDA decision on Merck & Co. Inc.’s (MRK) new supplemental Biologics License Application seeking approval to update the U.S. product label based on the phase 3 ZENITH trial for WINREVAIR is due on October 25, 2025. The ZENITH trial was designed to evaluate whether the addition of WINREVAIR could reduce the risk of death, lung transplantation, or pulmonary arterial hypertension (PAH) hospitalisations for patients living with advanced PAH. The trial was stopped early as WINREVAIR demonstrated a statistically significant and clinically meaningful reduction in the risk of morbidity or mortality events compared to placebo, both on top of background PAH therapy.WINREVAIR was approved in March 2024 for the treatment of adults with pulmonary arterial hypertension (PAH, World Health Organization [WHO] Group 1) to increase exercise capacity, improve WHO functional class (FC), and reduce the risk of clinical worsening events. The drug was approved based on the results of the STELLAR trial, which demonstrated that adding WINREVAIR to background therapy increased six-minute walk distance from baseline by 41 meters at Week 24 and significantly improved multiple important secondary outcome measures. The drug generated sales of $419 million in the full year 2024 and $616 million in the first half of 2025.MRK closed Friday’s (September 26, 2025) trading at $78.56, up 1.24%.