Enanta Pharmaceuticals has dosed the first patient in its global Phase IIb/III RESOLVE trial assessing zelicapavir in high-risk adult outpatients diagnosed with respiratory syncytial virus (RSV) infection.
Initial results from the Phase IIb segment of the programme are anticipated in 2027.
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The double-blind, randomised, placebo-controlled, multi-centre study is assessing the safety and efficacy of zelicapavir in adults presenting with respiratory symptoms lasting no more than three days and a confirmed RSV diagnosis.
Enrolled participants must be at least 75 years old, have chronic obstructive pulmonary disease, or suffer from congestive heart failure.
During the trial, subjects take an oral dose of 800mg of zelicapavir or a matched placebo once daily for seven days, followed by a 28-day assessment period.
The trial uses the duration until all 13 RSV symptoms fully resolve, measured using the RiiQ tool, as its primary endpoint.
Hospitalisation frequency serves as a key secondary measure, alongside overall safety, antiviral activity, and additional clinical efficacy outcomes.
At least 200 participants will take part in the Phase IIb portion to verify treatment effect sizes, while the Phase III stage is expected to enrol nearly 660 individuals.
Enanta Pharmaceuticals chief medical officer Scott Rottinghaus said: “We are excited to advance our zelicapavir programme into a Phase IIb/III study with the dosing of the first patient in RESOLVE. Based on learnings from our Phase II RSVHR study, the RESOLVE trial is enrolling adults at high risk for severe outcomes from RSV.
“The Phase IIb portion is designed to confirm the treatment effect size and generate an additional dataset with the goal of strengthening the clinical evidence supporting zelicapavir.
“Together with LOTUS, our paediatric Phase IIb trial, this progress positions us to deliver two important Phase IIb data readouts in 2027 and marks a significant step forward in the development of zelicapavir.”
Zelicapavir holds fast track designation from the US Food and Drug Administration. Unlike RSV fusion inhibitors that prevent viral entry, the compound inhibits the RSV N-protein to halt viral replication across RSV-A and RSV-B strains.
In earlier Phase II testing involving high-risk adults, the therapy shortened the time needed to resolve all 13 symptoms by 6.7 days compared to placebo in patients matching the RESOLVE criteria.
That earlier study also recorded an RSV-related hospitalisation rate of 0% in treated patients compared to 5% in the placebo cohort.
In a paediatric Phase II trial of children aged 28 days to three years, the therapy also demonstrated antiviral activity and accelerated symptom resolution. Across clinical trials, zelicapavir has been administered to more than 700 individuals.
Enanta Pharmaceuticals focuses on discovering small molecule treatments for immunological diseases and viral infections.
