# Ensitrelvir

Ensitrelvir, sold under the brand name Xocova is an antiviral medication used as a treatment for COVID-19. It was developed by Shionogi in partnership with Hokkaido University and acts as an orally active 3C-like protease inhibitor. It is taken by mouth.
The most common adverse events include transient decreases in high-density lipoprotein and increased blood triglycerides.

## Medical uses

Ensitrelvir is indicated for the treatment of COVID-19.

## History

As of 2022, ensitrelvir had reached Phase III clinical trials. The Japanese government is reportedly considering allowing Shionogi permission to apply for approval for medical use before the final steps of trials are completed, potentially speeding up the release for sale. This conditional early approval system has previously been used in Japan to accelerate the progression to market of other antiviral drugs targeting COVID-19, including remdesivir and molnupiravir. In a study of 428 patients, viral load was reduced, but symptoms were not significantly reduced.
In February 2022, the company sought emergency approval from regulators in Japan.
Shionogi announced they had reached a preliminary agreement to supply 1 million doses to the Japanese government once the drug is approved. The CEO said they could have capacity to make 10 million doses a year.
Ensitrelvir may be effective in treating smell and taste loss from COVID-19 infection. In a 2023 study, the drug was associated with a 39% reduction in these symptoms.

## Society and culture
### Legal status

Ensitrelvir was approved for emergency use in Japan in November 2022, before gaining full approval in March 2024. It was approved in Singapore in November 2023.
In April 2023, ensitrelvir was given a "Fast Track" designation from the US Food and Drug Administration.

### Names

Ensitrelvir is the international nonproprietary name (INN).

## Research

Ensitrelvir has been investigated for use as potential post-exposure prophylaxis (PEP) for SARS-CoV-2 infection. The SCORPIO-PEP trial, a global Phase 3 study, assessed the safety and efficacy of ensitrelvir in preventing symptomatic COVID-19 among household contacts of individuals with confirmed SARS-CoV-2 infection. Top-line results from this trial suggested that use of ensitrelvir as post-exposure prophylaxis may significantly reduce the risk of symptomatic COVID-19 infection in exposed household contacts compared to placebo.
An April 2024 pre-clinical study in a mouse model investigating ensitrelvir demonstrated its potential use as a pre-exposure prophylactic (PrEP) against developing COVID-19. When administered 24 hours before viral exposure, a single dose of ensitrelvir significantly increased survival rates, inhibited weight loss, and suppressed viral replication in aged mice.
A retrospective study conducted between November 2022 and July 2023 using a large Japanese health insurance database suggested that ensitrelvir may be effective in reducing hospitalization risk in outpatients at high risk for severe COVID-19. The study found a significantly lower risk of hospitalization and a reduced need for respiratory monitoring and oxygen therapy in the ensitrelvir group compared to the control group. In addition, other clinical study shows that early ensitrelvir treatment resulted in rapid symptom relief and significant viral load reduction, with no adverse events, viral rebound, or PASC symptoms, demonstrating its potential efficacy and safety.
In May 2024, Shionogi announced that in a phase 3 trial (SCORPIO-HR), ensitrelvir did not achieve its primary endpoint of a statistically significant reduction in the time to sustained resolution of 15 common COVID-19 symptoms compared to placebo. However, the drug did meet key secondary endpoints, including demonstrating a significant reduction in viral RNA levels, a shorter time to achieve the first negative infectious viral titer in nasal swabs compared to placebo, and a shorter resolution time of 6 symptoms.