Ensitrelvir, known as Xoxcova®125 mg in Japan, is an investigational oral 3CL protease inhibitor designed to suppress replication of the SARS-CoV-2 virus. While the drug has been given emergency regulatory approval in Japan, it is still an investigational agent outside the country.
The FDA’s decision to fast-track review of the antiviral was based on phase 3 data from the SCORPIO-SR study. SCORPIO-SR evaluated ensitrelvir safety and efficacy in persons with mild-to-moderate COVID-19 who were enrolled regardless of risk factors for COVID-19 progression. The cohort was more than 90% vaccinated against COVID-19. A total of 1203 patients from Japan, South Korea, and Vietnam received either ensitrelvir 125mg, with an initial loading dose of 375mg (n=603), or placebo (n=600) orally once daily for 5 days, within 5 days of symptom onset.
SCORPIO-SR investigators reported that treatment with ensitrelvir met the study’s primary endpoint demonstrating a statistically significant reduction in the time to resolution of 5 symptoms of COVID-19, compared with placebo (167.9 hours vs 192.2 hours; median time difference, 24.3 hours; P=.0407). Further, they observed a significant reduction in the time to achieve a negative infectious viral titer (secondary endpoint) in the ensitrelvir arm compared with the placebo arm (median time, 36.2 hours vs 65.3 hours; P<.001).
The phase 3 study was conducted during the Omicron-dominant phase of the epidemic.
There were no serious treatment-related adverse events during the study, according to the company statement, with the most commonly reported being a temporary decrease high-density lipoprotein and increased blood triglycerides, findings consistent with previous studies of ensitrelvir.
“There is a need for additional COVID-19 treatment options as SARS-CoV-2 continues to affect people in the US. Receiving Fast Track designation from the FDA recognizes the potential of ensitrelvir as a once-daily, oral antiviral for SARS-CoV-2,” said Nathan McCutcheon, CEO, Shionogi Inc, the US subsidiary of Shionogi. “We look forward to our continued discussions with the FDA to bring ensitrelvir to patients as soon as possible.”