FDA has cleared ArkBio to begin a Phase 2 clinical trial of ziresovir, an investigational antiviral treatment for infants with severe respiratory syncytial virus infection, including patients receiving care in pediatric intensive care units.
The multicenter, randomized, double-blind, placebo-controlled study will enroll hospitalized infants with severe RSV disease. It will evaluate ziresovir’s clinical efficacy, with particular attention to the duration of oxygen treatment and time to sustained recovery. The findings are intended to inform future registrational trials.
RSV is a major cause of lower respiratory tract infections in infants and young children. ArkBio said the virus causes about 33 million lower respiratory tract infection cases, 3.6 million hospitalizations and more than 100,000 deaths each year worldwide.
Severely ill infants may require intensive respiratory support in pediatric intensive care units because of rapid disease progression and the risk of serious complications. ArkBio said care remains largely limited to symptomatic and supportive measures, including oxygen therapy, leaving a need for effective antiviral treatments in hospitalized patients with severe disease.
Ziresovir, also known as AK0529, is a direct-acting RSV antiviral medicine. ArkBio said it is the first direct RSV antiviral to complete a Phase 3 clinical trial with positive results.
In a China-based clinical trial involving patients ages 1 to 24 months, ziresovir significantly reduced viral load and accelerated the resolution of respiratory symptoms, according to the company. ArkBio also said the therapy was associated with a lower risk of recurrent wheezing and asthma during a 24-month follow-up period and showed a favorable safety profile.
Results from ziresovir studies have been published in The New England Journal of Medicine and The Lancet Child & Adolescent Health. In 2025, the medicine was included as the only therapeutic drug in the World Health Organization’s Pediatric Drug Optimization for Respiratory Syncytial Virus publication, ArkBio said.
The newly cleared U.S. Phase 2 study extends the program into a more critically ill patient population than previously studied. ArkBio said the trial represents an important step in the global development of ziresovir and could provide evidence for future studies aimed at treating severe RSV infection in hospitalized infants.
Subscribe to our e-Newsletters
Stay up to date with the latest news, articles, and events. Plus, get special offers
from American Pharmaceutical Review – all delivered right to your inbox!
Sign up now!