Molnupiravir: Merck’s pill against Covid-19 could quickly be authorized in the United States

It may be less effective than expected, but has been approved by a committee of independent American scientists. This decision on molnupiravir, Merck’s pill against Covid-19 that could treat certain adults at risk, could pave the way for its probable authorization in the United States in the days to come. This drug has already been approved in early November in Great Britain, where it is marketed under the name Lagevrio. Antiviral treatments are eagerly awaited because they should make it possible to reduce the serious forms of Covid-19 using tablets taken simply at home, quickly after the onset of symptoms in the event of an infection.

The U.S. Medicines Agency (FDA), which called Tuesday’s meeting, will have the final say on granting emergency clearance for the drug, after the committee’s non-binding vote. He recommended that molnupiravir could be prescribed to people with mild to moderate cases of the disease who are at high risk of developing a severe case that could lead to hospitalization or death (in case of obesity, age advanced…). “This is the first opportunity for oral treatment to be available” outside the hospital for this population, said David Hardy, a member of the committee who spoke out for his emergency authorization.

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A “difficult” decision

The experts’ vote, which took place at the end of a day of discussions broadcast live, was however close, with 13 votes in favor and 10 against. Several called the decision “difficult”. They were particularly worried about the lower than initially anticipated efficacy of the treatment. According to data released Friday, the full results of the clinical trial on 1,400 participants showed a 30% reduction in the rate of hospitalization and death among at-risk patients. However, preliminary results, which only took into account a part of the participants in the trial, had initially put forward a figure of 50%.

The marked difference is due to a lower number of hospitalizations among people who received a placebo during the second half of the trial, which could not be clearly explained by the company. Merck, known as MSD outside of the United States, said in a presentation to the committee that it does not recommend the use of molnupiravir in pregnant women. On Tuesday, many experts on the committee also said that pregnant women should avoid taking this treatment, or at least favor others, such as synthetic antibodies, if available.

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Adverse effects?

In documents released Friday ahead of the meeting, the FDA noted certain adverse effects on fetal development during animal testing. Observations made on pregnant rats and rabbits have indeed shown that some litters had experienced more cases of malformation than in the control groups. Children are not affected by Tuesday’s decision, and pediatric testing is not considered until the results of ongoing tests on young rats. The treatment is administered within five days of the first symptoms, twice a day for five days. Molnupiravir works by introducing a mutation into the virus, which causes it to stop replicating.

Experts also raised concerns on Tuesday that the treatment could generate new, unwanted mutations in the virus, due to its technology. “The risk of mutagenic effects (…) is not firmly established or characterized,” said Sankar Swaminathan, a member of the committee, in explaining his vote against the recommendation. Daria Hazuda, a biochemist at Merck, however, stressed to AFP that “not treating patients and allowing the virus to evolve naturally (was) a much greater risk than the ability of molnupiravir to direct the evolution”.

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This mechanism also has an advantage over new variants. Unlike other treatments such as synthetic antibodies or vaccines, antivirals do not target the spike protein, which is used by the virus to enter cells. However, the Omicron variant has many mutations precisely on this protein, causing concern among experts as to the effectiveness of the remedies. On the contrary, Merck expects molnupiravir to have “similar activity against any new variant,” Daria Hazuda said during the meeting on Tuesday. Pfizer is also developing an antiviral treatment, the trade name of which is paxlovid, which works differently, by blocking an enzyme necessary for the virus to replicate. The United States has already ordered 3.1 million treatments from Merck and 10 million from Pfizer.

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