The data will be at the center of a panel discussion by US Food and Drug Administration advisers
Merck & Co said updated results showed its Covid-19 pill reduced the risk of hospitalization or death among adults with mild to moderate disease by 30%, less than a previous estimate and well below a rival treatment from Pfizer Inc.
Shares of Merck slid 3.4 per cent to $79.46 in pre-market trading, reversing earlier gains, while Pfizer rose 5.9 per cent.
Nine deaths were reported in the placebo group, and one in the group receiving the treatment, called molnupiravir.
The data will be at the center of a Tuesday panel discussion by US Food and Drug Administration advisers regarding its use to treat Covid in high-risk patients.
Merck sought US authorization for molnupiravir, also called Lagevrio, in October after a late-stage study showed it cut the risk of hospitalization or death by around 50% in high-risk patients. Another drug, Pfizer's Paxlovid, has been submitted for review for use in the same population after showing an 89% reduction.
If authorized by regulators, the pills from Merck and Pfizer are likely to overtake infused drugs monoclonal antibodies from Regeneron Pharmaceuticals Inc. and Eli Lilly & Co. that are more expensive and harder to use.
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