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Clinical Trial
. 2025 May;18(5):e70231.
doi: 10.1111/cts.70231.

EDP-323, a First-In-Class, Once-Daily, Oral L-Protein Inhibitor for the Treatment of RSV: Results From a Phase 1 Study in Healthy Adults

Kimberly Elmore  1 , John DeVincenzo  1 , Michael H J Rhodin  1 , Scott T Rottinghaus  1 , Alaa Ahmad  1
Affiliations
Clinical Trial

EDP-323, a First-In-Class, Once-Daily, Oral L-Protein Inhibitor for the Treatment of RSV: Results From a Phase 1 Study in Healthy Adults

Kimberly Elmore et al. Clin Transl Sci. 2025 May.

Abstract

Respiratory syncytial virus (RSV) remains a significant health concern, particularly for vulnerable populations. Despite preventive strategies, there remains a need for effective antiviral treatments. EDP-323 is a first-in-class, potent oral selective non-nucleoside inhibitor of the large protein (L polymerase) of RSV under investigation for the treatment of RSV infection. This phase 1, randomized, double-blind, placebo-controlled study evaluated the safety and pharmacokinetics of EDP-323. This study included fasted single ascending dose (SAD; EDP-323 50/100/200/400/600/800 mg doses, 3:1 to placebo), fed multiple ascending dose (MAD; EDP-323200/400/600/800 mg doses, 3:1 to placebo), and food effect (EDP-323200 mg dose, 4:1 to placebo) cohorts in healthy adult participants. Key objectives were to assess the safety, tolerability, and pharmacokinetic (PK) profile of EDP-323 in plasma and urine, and to evaluate the effect of food intake on its pharmacokinetics. Among 82 randomized participants (SAD, n = 50; MAD, n = 32), EDP-323 was well tolerated up to the highest tested dose (800 mg once daily for 7 days). Adverse events (AEs) were reported in 14.6% of total participants, with the majority being mild and deemed unlikely related to the study drug. Headache was the most frequent AE (n = 3). PK analysis showed that EDP-323 was rapidly absorbed (Tmax = 3.0-5.0 h), with exposures increasing with ascending dose. The half-life of EDP-323 (t1/2 = 10.8-16.6 h) supported once-daily dosing, and no food effect was observed. EDP-323 demonstrated a favorable safety and PK profile, supporting its potential as a once-daily oral treatment for RSV.

Keywords: clinical trials; healthy subjects; infectious disease; oral; pharmacodynamics; pharmacokinetics; phase I; safety.

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Conflict of interest statement

Medical writing assistance was provided by Shvetha Srinath, MSc, Katherine Stevens‐Favorite, PhD, and Brittany Eldridge, PhD, on behalf of Syneos Health, and supported by Enanta Pharmaceuticals.

All authors are currently employees of and hold stock in Enanta Pharmaceuticals Inc., Watertown, MA.

Figures

FIGURE 1
FIGURE 1
Study design. Healthy volunteers were randomized 3 (active): 1 (placebo), 4:1 in the FE cohort. All SAD participants were fasted except for those in a 200 mg FE cohort (high‐fat meal). All MAD participants were fed a standard meal. FE, food effect; MAD, multiple ascending dose; SAD, single ascending dose.
FIGURE 2
FIGURE 2
Mean EDP‐323 plasma concentration vs. time following oral administration of single doses on a linear scale (A) and log scale (B). Analysis was based on the PK set defined as all participants who received the study drug with a measurable plasma concentration of the study drug. PK, pharmacokinetic.
FIGURE 3
FIGURE 3
Mean EDP‐323 plasma concentration vs. time on Day 7 following oral administration of multiple doses on a linear scale (A) and log scale (B). Analysis was based on the PK set defined as all participants who received the study drug with a measurable plasma concentration of the study drug. PK, pharmacokinetic.
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