Oral Antiviral Candidate Shows Promise for RSV Treatment: Daily Dose

Patient Care brings primary care clinicians a lot of medical news every day—it’s easy to miss an important study. The Daily Dose provides a concise summary of one of the website's leading stories you may not have seen.

On January 30, 2025, we reported on preliminary findings from a phase 2 human challenge trial assessing S-337395 (Shionogi & Co. Ltd., UBE Corporation), an oral antiviral candidate, for the treatment of respiratory syncytial virus (RSV).

The medication

S-337395 is a low-molecular-weight compound that contains a novel mechanism that inhibits the ribonucleic acid (RNA)-dependent RNA polymerase activity of the L protein controlled by RSV, which is crucial for virus replication. The investigational therapy differs from the F protein inhibitors due to its role in preventing viral proliferation among infected cells, providing higher efficacy and a greater rapid reduction in the viral load.

The study

The randomized, placebo-controlled, double-blind human challenge study enrolled 114 healthy adults who were actively inoculated with RSV and received once-daily oral administration of S-337395 for 5 days. The primary endpoint was the area under the curve (AUC) of the viral load over time.

The findings

Individuals in the highest treatment dose group exhibited an 88.94% reduction in viral load (P < 0.0001) and a statistically significant improvement in clinical symptom scores compared to those in the placebo group.

The treatment was generally well tolerated, with no serious or severe adverse events reported and no dose-dependent increase in the incidence or severity of adverse events. No participants discontinued treatment due to adverse events.

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