Enanta Pharmaceuticals (ENTA) Study Result summary

Study design and objectives

• Phase II randomized, double-blind, placebo-controlled study in infants and children aged 28 days to 36 months with RSV infection, divided into two age cohorts.

• Study conducted in two parts: part one focused on dose finding (safety and PK), part two on virology (antiviral activity).

• Enrolled 99 patients, with 96 dosed; majority were hospitalized at baseline and baseline characteristics were balanced.

• Patients followed for 23 days post-treatment; dosing: 5 mg/kg for ages 28 days to <12 months, 7.5 mg/kg for ages 12–36 months, once daily for 5 days.

• Primary objectives: assess antiviral activity, safety, pharmacokinetics, and dose selection.

Efficacy and virology results

• Zelicapavir showed a 1.4 log viral load decline at day five in part two compared to placebo.

• In patients treated within three days of symptom onset, viral load declined by 0.9 log at day three and 1.2 log at day five versus placebo.

• Greater proportion of patients on zelicapavir had undetectable RSV RNA at days five and nine versus placebo.

• Antiviral effect was consistent across age groups and hospitalization status.

• Qualitative improvement in time to undetectable viral load observed at early timepoints.

Safety and tolerability

• Zelicapavir was well tolerated with a favorable safety profile; no adverse events led to discontinuation or withdrawal.

• Adverse events were similar between zelicapavir and placebo; most common were diarrhea and rash.

• Serious adverse events were infrequent and balanced between groups; one serious event (community-acquired pneumonia) was not related to the study drug.

• Target drug exposures achieved across all age groups and dosing cohorts, matching efficacious levels seen in adults.