COVID-19 patients who received the antiviral pill molnupiravir were clear of infectious SARS-CoV-2 virus activity by day three of treatment, according to new trial results. 

The federal government authorized the drug, made by Merck, for emergency use in December. It is indicated for COVID-19 patients with mild-to-moderate illness at risk for progression to severe disease. The drugmaker’s original clinical trial, MOVe-OUT, had found it to be 30% effective against COVID-19 progression when given within five days of symptom onset. 

The new Merck study analyzes the drug’s effect on the SARS-CoV-2 virus in infected patients. Investigators used frequent PCR COVID-19 tests to determine signs of active disease and potential transmissibility during treatment. 

No active virus detected

Participants received a five-day treatment course of twice-daily 800 mg pills. On treatment day three, there was no detectable active SARS-CoV-2 in any of the 92 participants treated with molnupiravir. In contrast, 22% of the 96 participants who received a placebo still tested positive for active virus, the researchers reported. 

By day five on the antiviral pills, viral activity had dropped sharply in the placebo group, with 2.2% still testing positive for activity. In contrast, the patients taking molnupiravir continued to maintain zero activity.

The recommended five-day treatment course for molnupiravir results in a more rapid decline in viral RNA and “faster elimination of infectious virus than placebo,” the researchers concluded.

Pills lead to faster clearance

“This study provides additional evidence that molnupiravir helps those infected clear SARS-CoV-2 faster than placebo, and supports MOVe-OUT’s primary finding that molnupiravir can lower the risk of progression to serious illness in this high-risk cohort,” they said.

Due to a relative lack of efficacy when compared to the antiviral Paxlovid, for example, and concerns about side effects, advisers to the Food and Drug Administration have recommended that the drug be used only in cases where more effective COVID-19 drugs were not available or were contraindicated.