The Medical Letter on Drugs and Therapeutics
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Molnupiravir - An Oral Antiviral Drug for COVID-19
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Merck and Ridgeback Biotherapeutics have announced that they will submit an application to the FDA for Emergency Use Authorization (EUA) for their investigational oral antiviral drug molnupiravir for treatment of COVID-19.1 If the EUA is granted, molnupiravir would be the first oral antiviral drug to be authorized in the US for treatment of COVID-19. The IV antiviral drug remdesivir (Veklury) was approved by the FDA for treatment of COVID-19 in hospitalized patients in October 2020.2

MECHANISM OF ACTION — Molnupiravir is a prodrug of the synthetic nucleoside derivative β-D-N4-hydroxycytidine. It targets viral RNA polymerase, resulting in the introduction of copying errors during viral RNA replication.3

CLINICAL STUDY — The efficacy of molnupiravir is currently being investigated in a randomized, double-blind, placebo-controlled phase 3 trial (MOVe-OUT) in non-hospitalized adult patients with mild to moderate COVID-19. Eligible patients had laboratory-confirmed SARS-CoV-2 infection with symptom onset within 5 days of randomization and at least one risk factor associated with poor disease outcome (e.g., obesity, age ≥60 years, diabetes, or heart disease). According to the results of a planned interim analysis released by the manufacturers, among 775 patients who were initially enrolled in the trial, molnupiravir reduced the risk of hospitalization or death through day 29 by approximately 50% (7.3% vs 14.1% with placebo). There were no deaths in the molnupiravir group compared to 8 deaths in the placebo group. The efficacy of the drug appears to be similar among the Gamma, Delta, and Mu variants. Based on these interim results, enrollment in MOVe-OUT has been stopped.1

ADVERSE EFFECTS — According to the manufacturers, adverse effects in MOVe-OUT were similar with molnupiravir and placebo. Fewer patients discontinued molnupiravir due to an adverse event (1.3% vs 3.4% with placebo).1

DOSAGE — The dosage of molnupiravir in the clinical trial was 800 mg twice daily for 5 days.4

CONCLUSION — The manufacturers of the investigational oral antiviral drug molnupiravir plan to file an application for Emergency Use Authorization (EUA) for the drug based on unpublished interim results of a randomized, placebo-controlled clinical trial which showed molnupiravir significantly reduced the risk of hospitalization or death in outpatients with mild to moderate COVID-19.

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