Representatives from Merck and from the F.D.A. reviewed the results of safety studies in cells, animals, and clinical trials. “The overall risk of mutagenicity in humans is considered low,” Dr. Aimee Hodowanec, a senior medical officer at the F.D.A., said at the meeting, referring to the potential for the drug to induce mutations in the DNA of people taking it.
However, when rats were given extremely high doses of molnupiravir compared to what people would get, they experienced some concerning effects. When pregnant rats got these high doses, their fetuses sometimes suffered deformities or died. Young rats that received high doses of molnupiravir experienced a disruption of their bone growth.
Children and pregnant women were excluded from the clinical trials of the drug.
Dr. Kartsonis said that while the company was not recommending use of the treatment in pregnant or breastfeeding women, it believes the F.D.A. should allow for exceptions in cases in which the benefit of treatment might outweigh the potential risks. He also said the company would start a pregnancy surveillance program to monitor the outcomes of women exposed to molnupiravir during pregnancy.
Britain, which authorized Merck’s pill earlier this month, recommended that it not be given to pregnant or breastfeeding women, and that women who could become pregnant use contraception while taking the drug and for four days after. The F.D.A. panel will discuss whether there are some situations in which the drug may be appropriate during pregnancy.
Dr. Kartsonis spent much of his presentation to the panel describing the interim results from the clinical trial, based on just 775 patients. In that analysis, molnupiravir reduced hospitalization and death by 50 percent. That result led the trial’s safety committee to halt the trial, since the benefit was already clear.
Within the last ten days, the full results from 1,433 volunteers were unblinded, Dr. Kartsonis said. Analyzing the full results, researchers found that the effectiveness dropped to 30 percent.
The drop was the result of a shift in outcomes in the trial. Late in the trial, a lower percentage of people who got the placebo ended up in the hospital. When asked to interpret the results, Dr. Kartsonis did not offer an explanation. “It doesn’t really add up to us,” he said.
Dr. Hodowanec said that the F.D.A.’s review of the full trial results “is currently ongoing.”
“As we enter the winter months, another surge is imminent,” Dr. Kartsonis said. “We remain in dire need of novel, effective well tolerated and conveniently administered therapies to treat Covid-19 in the outpatient setting.”