So-called anti-COVID pills are back in the news. U.S. Food and Drug Administration (FDA) advisers are meeting today to decide whether molnupiravir, a new antiviral for COVID-19 produced by Merck and Ridgeback Biotherapeutics, should be recommended for patients with coronavirus. If the panel votes to allow it, molnupiravir would be the first take-home oral drug approved to treat mild to moderate COVID-19, NPR reports. Paxlovid, a COVID-19 antiviral pill produced by Pfizer, is also currently under review by the FDA.
The hope is that these pills could have a significant impact in preventing people from suffering from the more severe stages of the disease. But how are anti-COVID pills supposed to work?
When the SARS-CoV-2 virus that causes COVID-19 enters our cells, it uses the cell’s own machinery to make copies of itself, heaps, heaps of copies. These copies leave the cell and then infect other cells, repeating the same process. Both pills aim to work by reducing the virus’s ability to replicate in our system, but their methods are different.
Molnupiravir is called a polymerase inhibitor. It tricks polymerases, which are enzymes that copy ribonucleic acid for the virus, by creating mutation errors. Instead of the original virus being copied, this new error is copied instead, until there are so many errors that the virus cannot survive. However, there are some concerns that the drug may affect other enzymes in our body, because NBC News reports, especially if taken for a longer period of time. A course of molnupiravir would be 40 tablets prescribed over five days.
Paxlovid, on the other hand, uses an experimental molecule called PF-07321332 that works as a protease inhibitor, like CNBC Explain. Protease is an enzyme that splits viral proteins so that they can spread more easily. Paxlovid essentially dulls the protease, not allowing it to slice up proteins. The larger strands of viral protein do not allow the virus to replicate. Unlike the drug from Merck, no mutation is introduced. A course of Paxlovid would be 30 tablets over five days (some being Paxlovid and others the antiviral ritonavir, which appears to help keep Paxlovid in the body longer).
Initial data from Merck’s clinical trials suggests that high-risk unvaccinated people with mild or moderate COVID-19 who started taking molnupiravir within five days of the onset of their symptoms saw a 50% reduction in hospitalizations and deaths, compared to those who received a placebo. But the final analysis of the clinical trial suggested only a 30% decrease in hospitalizations and deaths compared to the placebo groups, the New York Times reports.
Pfizer’s early clinical trials look more promising. For unvaccinated patients with at least one disease that made them at high risk, those who took Paxlovid within three days of the onset of their symptoms saw an 89% reduced risk of hospitalization and death because the New York Times reports. For people who started within four or five days of symptoms, their risk was reduced by 85%.
Currently, the only treatment approved by the FDA for COVID-19 patients with mild to moderate cases (and who are at high risk of becoming seriously ill) are monoclonal antibodies, which reduce the risk of hospitalization and death by 70 %. Monoclonal antibodies are laboratory-made molecules that replace natural antibodies in people who have never been vaccinated or infected before, and they can also help build existing immunity, according to the FDA. They can help prevent the virus from attaching to human cells and they can help neutralize the coronavirus. (Remdesivir, which you may also have heard of, is FDA approved specifically to treat COVID-19 cases requiring hospitalization, not mild or moderate ones.)
Monoclonal antibodies should be delivered intravenously and in a clinical setting. As NPR explains, the pills are said to be easier for people to obtain, easier to take, and they are much cheaper to manufacture. But first, we’ll have to wait for the verdict from the FDA.