The US Food and Drug Administration (FDA) has issued emergency use authorization to a second oral COVID-19 treatment. Called molnupiravir the new drug is not as effective as Pfizer’s recently approved COVID antiviral pill, and many experts suggest the FDA should never have authorized it in the first place as it has the potential to generate new SARS-CoV-2 variants.
Just a few months ago molnupiravir, being developed by pharma giant Merck, was being mooted as a game-changing new drug that could turn the tide of the pandemic. It was one of the first antiviral pills to directly target SARS-CoV-2, and a preliminary Phase 3 trial announcement indicated promising efficacy.
But as the weeks passed molnupiravir quickly lost its luster. Pfizer’s novel antiviral pill raced to the head of the pack with impressive clinical trial data, while a final analysis of molnupiravir’s Phase 3 data revealed a stark drop in efficacy, down to levels bordering on insignificant.
While Pfizer’s final trial analysis reported up to 90 percent protection from COVID-19 hospitalization or death, molnupiravir’s efficacy strangely dropped from interim analysis to final reporting. Initially Merck announced molnupiravir delivered around 50 percent protection from COVID-19 hospitalization or death but a final trial analysis weeks later revealed that efficacy had dropped to barely 30 percent.
Alongside the disappointing efficacy data, questions began to arise over the drug’s safety profile, on both individual and societal levels.
Molnupiravir is a very different drug to Pfizer’s COVID antiviral Paxlovid. Pfizer’s drug is specifically targeted at SARS-CoV-2, working to inhibit the activity of a key enzyme the virus needs to replicate. Molnupiravir, on the other hand, targets RNA viruses in general. It was originally developed in 2018 as a tool to treat influenza, and lab work revealed it potentially worked against other RNA viruses including Ebola and the first SARS coronavirus.
It works by generating transcription errors as a virus replicates. This essentially produces a massive volume of downstream mutations in a virus as it replicates and this quickly leads to major dysfunction in the viral copies.
While there were no significant adverse effects reported in molnupiravir’s Phase 3 clinical trial, its particular mode of action has concerned some experts who argue this mutagenic mechanism could theoretically cause problems in some fast-growing human cells. As an FDA advisory panel debated the safety and efficacy of molnupiravir in late November, the main safety issue they raised was whether the drug should be offered to someone who is pregnant.
The independent advisory panel ultimately voted to recommend approval of molnupiravir, but the result was far from unanimous. A divisive 13-10 vote led a Merck representative at the meeting to affirm the company would not recommend pregnant individuals take the drug. However, the representative also indicated these decisions should be made in conversation between patients and their individual doctors.
“We would not recommend its use in pregnancy and we would also recommend contraception in women of childbearing age,” the Merck representative was reported as saying. “But I think the idea here is that ultimately the physician is the best position to determine the relative risk benefit for their patients.”