Merck's Winrevair Secures FDA Label Expansion, Solidifying Its Blockbuster Potential

Merck's strategic acquisition of Acceleron in 2021 continues to bear fruit as the pharmaceutical giant secures a significant label update for its pulmonary arterial hypertension (PAH) treatment, Winrevair. The U.S. Food and Drug Administration (FDA) has approved an expansion to Winrevair's label, highlighting its ability to reduce the risk of hospitalization, lung transplantation, and death in PAH patients.

Zenith Trial Results Pave the Way for Label Update

The label expansion is based on the compelling results from the phase 3 Zenith trial, which was halted early due to overwhelming efficacy. The study, which enrolled 172 high-risk PAH patients classified as World Health Organization Functional Class (FC) III or IV, demonstrated that Winrevair, when added to maximum background therapy, reduced the risk of clinical worsening events by an impressive 76% compared to placebo.

Dr. Vallerie McLaughlin, a professor of cardiovascular medicine at the University of Michigan, emphasized the significance of these results, stating, "For patients with PAH, the risk of serious events such as hospitalization, transplantation or death remains unacceptably high despite being maximally treated with traditional therapies. Results from the pivotal Zenith trial add to the growing body of data and support the potential for Winrevair as standard of care."

Winrevair's Mechanism and Market Potential

Winrevair, a first-in-class activin signaling inhibitor, works by rebalancing cell signaling in PAH patients. The rare disease affects approximately 40,000 people in the United States, predominantly middle-aged women. PAH is characterized by thickened and narrowed blood vessels in the lungs, leading to increased blood pressure and potential heart failure.

Since its initial approval in March 2024, Winrevair has shown strong market performance. In the second quarter of 2025, the drug generated revenue of $336 million, up from $280 million in Q1. Following the Zenith trial results, analysts at Citi have revised their 2030 sales estimates for Winrevair to a range of $5.7 billion to $6.1 billion, solidifying its status as a potential blockbuster drug.

Implications for PAH Treatment Landscape

The expanded label and robust clinical data position Winrevair as a potential game-changer in the PAH treatment landscape. As the first therapy to demonstrate such significant risk reduction in hospitalization, transplantation, and mortality, Winrevair may become the new standard of care for high-risk PAH patients.

With this latest development, Merck's $11.5 billion acquisition of Acceleron in 2021 appears increasingly prudent, potentially reshaping the company's position in the rare disease market and providing new hope for patients living with this challenging condition.