Enanta fails its first respiratory syncytial virus test

There are good reasons why developers avoid testing potential new medicines in not-very-sick people who are likely to get better quickly. For one, proving a benefit is tough, an issue that tripped up some Covid antiviral developers, and one that has now set back Enanta’s hopes in respiratory syncytial virus. A phase 2b trial of the oral antiviral EDP-938 conducted in otherwise healthy patients with RSV failed, with misses on both the primary endpoint, which looked at symptom scores, and secondary antiviral measures. Enanta attempted a somewhat flimsy defence of the project’s activity: more EDP-938 than placebo patients had no detectable viral RNA at the end of treatment, it said, but this claim is weakened by the failure of the study. Last week the company presciently announced plans for a trial in high-risk patients, but results from that and other ongoing studies are unlikely to emerge until next year, meaning that it will be a while before investors can figure out whether Enanta tripped itself up here, or if ‘938 is a dud. J&J recently dropped out of this narrow field, so there is certainly opportunity, but RSV has long been a tricky space. Enanta stock dropped 7% this morning. 

A thin pipeline: selected clinical-stage antivirals in development for RSV 
Project Company Description Status
Ziresovir (AK0529) Arkbio  RSV F-protein fusion inhibitor Ph3 Airflo trial in Chinese hospitalised infants said to have succeeded; ex-China development unclear
EDP-938 Enanta N-protein inhibitor Ph2 RSVP in low-risk adults failed; RSVPEDs in hospitalised/non-hospitalised children & RSVTx in immunocompromised adults due 2023; ph2b in high-risk adults to start Q4'22
Sisunatovir Pfizer (via Reviral) RSV F-protein fusion inhibitor Ph2 Reviral 1 in hospitalised infants completes Nov 2023; Reviral 2 in immunocompromised adults completes Jun 2023
RSV-N* Pfizer (via Reviral) N-protein inhibitor Ph1
Rilematovir (JNJ-53718678) Johnson & Johnson RSV F-protein fusion inhibitor Ph3 Daisy and ph2 Primrose terminated in April (no reason given, CT.gov states no safety concerns)
*Route of admin for this project not disclosed, assumed oral. Source: Evaluate Pharma & clinicaltrials.gov.

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