Ensitrelvir’s Impact in COVID-19 Symptom Management and Relief

Women taking an antiviral pill.

Shionogi & Co, Ltd disclosed the outcomes of their pivotal phase 3 study, SCORPIO-HR, conducted globally to evaluate the efficacy of ensitrelvir (Generic name: ensitrelvir fumaric acid, Code No: S-217622), aimed at combating COVID-19 symptoms. The study did not meet its primary goal of achieving a statistically significant reduction in the time to sustained resolution of 15 common COVID-19 symptoms when ensitrelvir was administered once daily within 3 days of symptom onset compared to a placebo.

A predefined secondary analysis focusing on the resolution of 6 symptoms did reveal a significant disparity (p<0.05) in the time taken for symptom resolution. Ensitrelvir exhibited a robust antiviral effect, leading to a marked reduction in viral RNA levels and viral culture positivity compared to the placebo. There were no instances of symptomatic viral rebound observed during the study, consistent with prior findings from SCORPIO-SR.

The SCORPIO-HR trial encompassed a diverse cohort of symptomatic, non-hospitalized COVID-19 patients, irrespective of previous SARS-CoV-2 infection, across regions where the Omicron variant was prevalent. Most participants had received vaccinations, and 30% had underlying risk factors for severe disease such as obesity, hypertension, or diabetes mellitus.

Key Takeaways

  1. The primary endpoint of the SCORPIO-HR study was the time to sustained symptom resolution (the first day of 2 consecutive days with complete resolution of 15 common COVID-19-related symptoms).
  2. Although ensitrelvir demonstrated a numerical reduction in the time to symptom resolution compared to placebo among participants treated within 3 days of symptom onset, the difference was not statistically significant.
  3. A pre-defined supportive analysis of resolution of 6 symptoms for one day using a statistical method similar to that used in the SCORPIO-SR Study (Phase 3 part of the Phase 2/3 study of ensitrelvir conducted in Asia) yielded a significant difference (p<0.05) in the time to resolution of symptoms.

For the primary analysis, the median time to symptom resolution was approximately 7 days (ensitrelvir group) vs 8 days (placebo). Participants were administered a once-daily ensitrelvir, 125mg, and those included in the primary analysis were randomized less than 72 hours from symptom onset. More than 90% of patients had received 2 or more doses of the COVID-19 vaccine and patients were included regardless of risk factors for severe disease.2

The study also met its 2 key secondary endpoints (primary analysis population). The amount of viral RNA was significantly lower on day 4 in the 125 mg ensitrelvir group compared with placebo (least squares mean change from baseline -2.48 log10 copies/mL versus -1.01 log10 copies/mL, p<0.001).2

The time to achieve the first negative infectious viral titer in nasal swabs, indicating clearance of infectious virus from the upper airways was significantly shorter in the ensitrelvir 125 mg group compared with placebo (a median time of 36.2 hours versus 65.3 hours, p<0.001).2

This trial is part of the National Institutes of Health’s (NIH) Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV) initiative and is being conducted collaboratively by Shionogi, the National Institute of Allergy and Infectious Diseases (NIAID), and the ACTG global clinical trials network, primarily focused on HIV and other infectious diseases and funded by NIAID.

Ensitrelvir was granted Fast Track designation by the US Food and Drug Administration (FDA) in 2023, aimed at expediting the development and review process for drugs addressing medical needs. In Japan, where it is marketed under the brand name Xocova, ensitrelvir received emergency regulatory approval in 2022 and obtained full approval in March 2024. Over a million individuals have been treated with ensitrelvir since its emergency approval in Japan. Additionally, ensitrelvir secured approval in Singapore through a Special Access Route application in 2023.

Ensitrelvir’s mechanism of action involves selectively inhibiting the 3CL protease enzyme of SARS-CoV-2, crucial for the virus’s replication. Its Fast Track designation underscores its potential in addressing effective COVID-19 therapeutics, while its regulatory approvals in Japan and Singapore mark milestones toward global recognition and accessibility.

  1. SHIONGI. Shionogi Provides Updates from SCORPIO-HR, a Global Phase 3 Study of Ensitrelvir for Non-Hospitalized Participants with COVID-19. Published May 13, 2024. Accessed May 14, 2024.
  2. Parkinson J. Antiviral Reduces Time to Resolution of Symptoms in Mild to Moderate COVID-19. Contagion. Published February 26, 2024. Accessed May 14, 2024. https://www.contagionlive.com/view/antiviral-reduces-time-to-resolution-of-symptoms-in-mild-to-moderate-covid-19

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