Treatment with ensitrelvir, an oral SARS-CoV-2 3C-like protease inhibitor developed in Japan, shortened COVID-19 symptoms in people who received the medication within 3 days of symptom onset, researchers reported recently in JAMA Network Open.
In 2023, the drug—made by Shionogi—was authorized for emergency use in Japan and received a fast-track review designation from the US Food and Drug Administration.
The randomized clinical trial took place between February 2022 and July 2022 when the Omicron BA.2 variant was circulating at clinical sites in Japan, Vietnam, and South Korea. The study population included mostly healthy people ages 12 to 69 years old who had mild to moderate COVID symptoms and a positive test for the virus. About 91% had previously received two doses of COVID vaccine.
Researchers evaluated two different ensitrelvir doses given for 5 days against placebo. One dose was 125 mg given once a day (375 mg on the first day), and the other was 250 mg once daily (750 mg on the first day). Researchers followed the groups for 28 days, monitoring symptoms including runny nose, sore throat, shortness of breath, and cough, as well as any side effects.
Symptoms shortened from 5 days to 4 days
They saw a significant difference between the 125-mg dose and placebo, with treatment shortening symptoms by 1 day, from 5 days to 4 days. There were no serious adverse events, but people who took ensitrelvir had temporary reductions in their high-density lipoprotein levels. In the secondary analysis, treatment also reduced viral loads when compared to placebo.
The team said more studies need to be done to assess efficacy in populations outside of Asia and in people who have a range of different risk factors.