Merck's shares fell 3.5 % in premarket trading on Friday as the firm awaits the results of the FDA's examination of the COVID-19 tablet it co-developed with Ridgeback Biotherapeutics.
The stock originally rose 1.2 % but was dragged down by broader market fears about the appearance of a new coronavirus type in South Africa.
The firms say that molnupiravir, an antiviral medication, lowers the risk of hospitalization or death in individuals with COVID-19's current prevalent strain.
There is no evidence that the medicine molnupravir would work against the new strain.
A study of clinical-trial data for molnupiravir will be covered in a report from FDA staff, which is expected on Friday. The FDA staff's opinion on whether the medicine should be approved for usage may also be included in the report.
Molnupiravir could be the world's first oral antiviral medication for COVID if it is authorized.
The company has stated that if the emergency use approval is granted in December, the medicine could generate up to $7 billion in revenue in 2022, including $1 billion this year.
The medication is quite inexpensive to produce and distribute. Merck plans to produce 10 million treatment courses by the end of 2021, with more doses coming in 2022. It has pledged to furnish the US government with 3.1 million courses, assuming all appropriate permits are granted.
Merck's antiviral tablet, along with treatments from Pfizer and Regeneron, is one of just three oral medicines that show success against Covid-19 thus far. According to Pfizer, the risk of hospitalization or death is reduced by 89 %.