Shionogi has announced that ensitrelvir, its oral antiviral Covid-19 drug, has met primary and key secondary endpoints in the Phase III segment of the SCORPIO-SR study.

SCORPIO-SR is a randomised, double-blind, placebo-controlled Phase II/III study enrolling mild to moderate Covid-19 patients.

The Phase III trial included patients in South Korea, Japan, and Vietnam.

Ensitrelvir is claimed to be the first antiviral agent to demonstrate improvement in clinical symptom and antiviral effect in a vaccinated population infected with the Omicron variant of the SARS-CoV-2 virus.

In the primary analysis group, ensitrelvir led to a statistically significant decline in the time to resolution of five common symptoms of Covid-19 compared to placebo.

Furthermore, the median time to symptom resolution was nearly one day shorter in the ensitrelvir arm versus placebo.

Subjects in the study were treated within 72 hours from the development of symptoms, and more than 90% had received a minimum of two doses of a Covid-19 vaccine.

On secondary endpoints, a less amount of viral ribonucleic acid (RNA) was seen in ensitrelvir group on day four compared to placebo.

Additionally, the time to achieve the first negative infectious viral titer in nasal swabs was significantly shorter for patients receiving ensitrelvir, indicating a quicker clearance of the infectious virus from the upper airways.

Regarding safety, most adverse events reported in the trial were mild, with no deaths observed.

The common treatment-related adverse events included temporary decline in high-density lipoprotein and increases in blood triglycerides.

Ensitrelvir, known as Xocova in Japan, received emergency regulatory approval from the Ministry of Health, Labour and Welfare in Japan in 2022.

In November 2023, it was also approved in Singapore based on the Special Access Route application. However, it remains under investigation in other regions.

The US Food and Drug Administration has granted fast track designation for the antiviral drug.

Shionogi Drug Development and Regulatory Science senior vice-president Takeki Uehara said: “These results demonstrate accelerated resolution in a range of symptoms, reinforcing the potential of ensitrelvir across multiple patient profiles.

“Additionally, ensitrelvir reduced viral RNA levels and time to first negative viral titer, suggesting it could help reduce transmission of SARS-CoV-2.”