Evaluation of zelicapavir for pediatric RSV

Female adult helps small child with RSV use nebulizer.

Enanta Pharmaceuticals, Inc., announced positive topline results from its phase 2 study evaluating zelicapavir in hospitalized and non-hospitalized children aged 28 days to 36 months with respiratory syncytial virus (RSV). This is the first pediatric assessment of zelicapavir, a novel N-protein inhibitor in development as a once-daily oral treatment for RSV.

Investigators observed an antiviral effect for the primary and secondary virology endpoints in the overall population. The study showed a pronounced antiviral effect with a viral load decline of 1.4 log at the end of treatment (day five) compared to placebo. Additionally, a prespecified subset of pediatric patients who joined the trial within three days of symptom onset witnessed a 1.2 log decline in viral load at day five compared to placebo. 

The company also reported zelicapavir demonstrated a favorable safety profile and was well-tolerated in this pediatric population.

“These data provide us with continued confidence in zelicapavir and valuable insights to inform the design of a potential registration enabling trial,” said Scott T. Rottinghaus, MD, chief medical officer of Enanta Pharmaceuticals, in a press release.

The phase 2 randomized, double-blind, dose-ranging, placebo-controlled study included a total of 96 patients, who were treated with zelicapavir (n=70) or placebo (n=26). The primary objective of part 1 of the study was to evaluate the safety and pharmacokinetics of zelicapavir and to determine the optimal dosing for part 2 of the study. In both parts, patients received either the drug or placebo once daily for five days. 

Zelicapavir achieved target drug exposure levels across all age groups and dosing cohorts. A dose of 5 mg/kg was selected for patients 28 days to 12 months old. A dose of 7.5 mg/kg was selected for patients 12 to 36 months of age.

“In my practice, I see many children requiring hospitalization for severe RSV infection during the RSV season,” said principal investigator Jaime Deville, MD, FAAP, professor of clinical infectious diseases in the Department of Pediatrics at the David Geffen School of Medicine, UCLA, and UCLA Mattel Children’s Hospital. “The impact of RSV is felt not only by patients and caregivers, but also broadly by public health. I believe that a safe and effective antiviral therapeutic is critical in addressing this significant and unmet need.”

Zelicapavir demonstrated a favorable safety profile over the five-day dosing period and through the follow-up period of 23 days. Adverse events of zelicapavir were similar to those of the placebo, and there were no AEs leading to treatment discontinuation or study withdrawal. 

The research team balanced demographics and baseline characteristics across treatment groups, with the majority of patients hospitalized at enrollment, and a mean duration of RSV symptoms prior to randomization of four days. Virology results were similar regardless of age or whether patients were enrolled from a hospital or outpatient setting.

The U.S. Food and Drug Administration (FDA) previously granted Fast Track designation for zelicapavir. Enanta Pharmaceuticals said it will present complete study results at a later date.

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