Merck said on Friday (Nov 26) that updated data from its study on its experimental COVID-19 pill showed the drug was less effective in cutting hospitalisations and deaths than previously reported.
The drugmaker said its pill showed a 30 per cent reduction in hospitalisations and deaths, based on data from more than 1,400 patients.
In October, its data showed a roughly 50 per cent efficacy, based on data from 775 patients.
Merck's shares fell 3 per cent to US$79.80 in premarket trading, amid a fall in the broader markets.
The company filed for a US authorisation of the drug molnupiravir on Oct 11, following the interim data.
Merck said on Friday the data on molnupiravir, developed with Ridgeback Biotherapeutics, had been submitted to the US Food and Drug Administration ahead of a meeting of its expert advisers on Tuesday.
The FDA's scientists are expected to publish their briefing documents ahead of the meeting as early as Friday.
The panel is expected to vote whether to recommend that the agency authorise the oral capsules for the treatment of mild-to-moderate COVID-19 in adults who are at risk of severe disease.
A planned interim analysis of the data last month showed that 7.3 per cent of those given molnupiravir twice a day for five days were hospitalised and none had died by 29 days after the treatment.
That compared with a hospitalisation rate of 14.1per cent for patients on placebo.
In the updated data, 6.8 per cent of those given molnupiravir were hospitalised and one person died, while the other placebo group had a hospitalisation rate of 9.7 per cent.