Merck and Pfizer Seek Approval for COVID-19 Antiviral Drugs

Merck and Pfizer have submitted Emergency Use Authorization (EUA) applications to the U.S. Food and Drug Administration (FDA) to authorize distribution of what would be the first antiviral drug specifically designed to treat COVID-19 disease.¹

Merck/Ridgeback Biotherapeutics are seeking EUA approval for Molnupiravir (MK-4482/EIDD-2801), an investigational oral antiviral drug originally developed to treat influenza.² Pfizer is seeking EUA approval for their oral antiviral candidate, Paxlovid (PF-07321332; ritonavir) for the treatment of mild to moderate COVID disease.³

Molnupiravir Comes With Risks

Molnupiravir is a polymerase inhibitor. Polymerase inhibitors stop the genetic material of a virus from being replicated by tricking the enzyme (called a polymerase) responsible for replicating the virus’s RNA by inserting errors and mutations. The mutations then get replicated over and over, until there are numerous mutations making it difficult for the virus to survive.⁴

Katherine Seley-Radtke, PhD, a medical chemist at the University of Maryland who specializes in antiviral drug development maintains that the drug’s mutation/error catastrophe method is effective. However, she says it is “a little bit risky, because it could also hit human host enzymes, as well.”⁵

Some scientific research suggests that drugs like Molnupiravir can affect other enzymes in the body when taken for longer periods of time. Although Molnupiravir is to be taken at home as four capsules twice a day for five days, for a total of 40 pills,⁶ Dr. Seley-Radtke says “it still causes concerns.”⁷

Paxlovid Combines an Older Drug With an Experimental Molecule

Pfizer’s Paxlovid antiviral pill is to be administered in combination with an older antiviral drug called ritonavir and is designed to treat mild to moderate COVID in patients at increased risk of hospitalizations or death.⁸

Paxlovid’s mechanism is very different from the one used in Molnupiravir. Pfizer describes how Paxlovid works…

PF-07321332 is designed to block the activity of the SARS-CoV-2-3CL protease, an enzyme that the coronavirus needs to replicate. Co-administration with a low dose of ritonavir helps slow the metabolism, or breakdown, of PF-07321332 in order for it to remain active in the body for longer periods of time at higher concentrations to help combat the virus.

PF-07321332 inhibits viral replication at a stage known as proteolysis, which occurs before viral RNA replication. In preclinical studies, PF-07321332 did not demonstrate evidence of mutagenic DNA interactions.⁹

Vaccination Advocates Want to Prioritize COVID Vaccinations, Not Drug Treatments

Some vaccination advocates are concerned that the COVID pills will further deter unvaccinated people from getting vaccinated, arguing that although the antiviral COVID pills may be effective in treating the infection, getting unvaccinated people to take COVID vaccines should be a priority.¹⁰

Scott Ratzan, MD, a lecturer at City University of New York (CUNY) School of Public Health, noted that, in a preliminary survey of 3,000 people led by his team, one out of every eight survey respondents said they would rather be treated with a pill after getting infected than get vaccinated.¹¹

“The new COVID pills are a big deal but vaccinations will always be the cornerstone of our response to COVID,” Dr. Ratzan said. “The oral medication represents a significant improvement in our ability to treat COVID and avert further deaths, but we must stay focused on fully vaccinating as many people as possible. Only a vaccine can control the rate at which a virus spreads and mutates.”¹²

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