Key advisers to the Food and Drug Administration are scheduled to meet Tuesday to decide whether to recommend that the agency grant emergency use authorization to Merck's experimental pill to treat Covid-19.
Members of the agency's Antimicrobial Drugs Advisory Committee will scrutinize the company's data before voting on whether the drug's overall benefits outweigh its risks. The FDA doesn't have to follow the committee's advice, but it often does.
Merck asked the FDA in October to clear its drug, called molnupiravir, for use in adults with mild-to-moderate Covid-19 who are at risk for severe disease or hospitalization. If granted emergency use authorization, it would be the first antiviral pill to treat the disease. All other FDA-backed treatments require an IV or injection.
Results released Friday by Merck showed the drug reduced the risk of hospitalization and death among high-risk Covid patients by 30 percent. That's down from an estimate of 50 percent the company made in October, and lower than currently authorized monoclonal antibody treatments, which have been shown to reduce the risk of severe outcomes from Covid by at least 70 percent.
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FDA scientists also noted potential risks of the drug, particularly to pregnant women, as animal studies suggest it could cause harm to the fetus or possible birth defects. These risks were not observed in the clinical trials, however, because pregnant women were excluded from Merck's study and the use of contraception was required for all participants, the agency said.
The drug — developed in partnership by Merck and Ridgeback Biotherapeutics — works by introducing errors, or mutations, into the virus's genetic material that make it difficult for the virus to replicate. It takes a different approach than another antiviral pill, developed by drugmaker Pfizer, which blocks an enzyme the virus needs to replicate. Scientists say both drugs need to be taken in the early stages of the disease to be effective; in Merck's study, participants were given the drug within five days of symptom onset.
Dr. David Boulware, an infectious disease physician at the University of Minnesota Medical School, said he expects the committee to endorse molnupiravir for most high-risk adults. While the efficacy of the drug was found to be "substantially" lower than previously estimated, it could still be helpful, he said.
Physicians are still going to want to "recommend monoclonal antibodies. They're better," he said. "Still, this is kind of an option for people that don't have access to those treatments or other factors come into play."
The benefit of being able to prescribe something in the middle of the night or on weekends, and have a patient just go to their local pharmacy to pick up the pills cannot be overstated, Boulware said. Uptake is likely to be better for a pill than monoclonal antibody treatments, which require an infusion.
Initially, demand for Merck's drug could outstrip supply, Boulware said; the federal government has agreed to purchase about 3.1 million courses of molnupiravir for $2.2 billion, with the option to buy more.
Demand for the drug could also wane after the anticipated authorization of Pfizer's oral antiviral treatment, which has been shown to cut the risk of hospitalization and death by 89 percent and may be safer for some groups, such as pregnant women, he said.
No major safety concerns were identified in the clinical trial data for Merck's pill, though the drug may increase the rate of changes in the virus's spike protein, "which, in theory, could enhance SARS-CoV-2 spike protein evolution," the FDA said.
The agency also pointed out that Merck's safety dataset, which included 593 people, was notably smaller than those provided for other therapies authorized for the treatment of mild-to-moderate Covid.
Ronald Swanstrom, a biochemistry professor at the University of North Carolina School of Medicine, said he hopes the FDA committee discusses the potential long-term consequences of using the drug, including its potential impact on human DNA.
He and his colleagues published a study in The Journal of Infectious Diseases this year that found that a byproduct of the drug induced low levels of mutations in the DNA of animal cells, suggesting it could pose a risk of cancer. Merck later pushed back on the study.
The mutations could be "trivial," Swanstrom acknowledged. "Every time you go to get a dental X-ray, you've got these X-rays firing through your head and that's doing DNA damage. The bulk of the experience we have is, it's not enough to make a difference in any of our health outcomes."
Still, for Merck's drug, "we have no idea what the level of risk is and that's a problem," he said.
"We should be careful on who we give the drug to and we should set up a cohort and find out what the long-term consequences are," he said.
Dr. Paul Offit, a vaccine expert at Children's Hospital of Philadelphia, said that while vaccination remains the best form of protection against the virus, pills like Merck's could keep the disease from progressing in those who do get infected and prevent trips to the hospital. He said he does worry about side effects though.
He also said he doesn't expect that authorization of the pill will sway unvaccinated people to get their shots. Many of them made up their minds about the vaccines a long time ago, he said.
"I think at this point if you're choosing not to get a vaccine, you're entrenched," he said. "There's nothing that's going to convince you at this point."