In these pages last March, I reminded readers to be thankful for the vaccines that prevent COVID-19, but to not forget the antiviral drugs that are being developed that might treat the disease. Both vaccines and antivirals are part of the same quiver of weapons we have to fight the pandemic. In that blog post, I mentioned an experimental drug, molnupiravir that was being developed by Merck and Ridgeback Therapeutics. Well, they just posted an encouraging update. It continues to show success at preventing serious disease when given to high-risk people early after infection. Its only side effects were similar to the placebo, meaning it is very safe. In animal studies, the drug also was effective against different CoV-2 variants, including Delta, and against other coronaviruses including SARS and MERS. Molnupiravir is a “prodrug,” which means that it has no activity on its own; rather it is metabolized after ingestion to an active drug that was developed in the early 2000s to treat hepatitis C.
This is a significant step for being able to easily protect high-risk patients at home. The pill that patients take on their own cuts their risk of hospitalization or death by ~50%. The results were so encouraging that the study was halted after consultation with the FDA. Early termination of studies like this is only done when interim data analyses show such good efficacy of a treatment that it would be unethical to continue enrolling subjects, some of whom would receive placebo, thereby being denied an effective therapy.
The drug slows the spread of the virus in infected people by forcing the enzyme that copies the viral genetic material into making so many mistakes the virus cannot reproduce. That, in turn, reduces the patient’s viral load, shortening the infection and damping the type of over-exuberant immune response (cytokine storm) that causes serious problems in many COVID patients. It was not effective when given to already hospitalized, or advanced, patients. It is on track to be approved by the FDA by the end of the year, and would be the first proven and approved oral antiviral drug for treating COVID-19 (neither ivermectin nor hydroxychloroquine have been proven or approved).
The FDA has already cleared another antiviral drug, remdesivir, for treating COVID-19, but it is only used to treat advanced patients who are already hospitalized (interestingly remdesivir was also originally developed to treat hepatitis C and it is also used to treat Ebola). Several lab-produced monoclonal antibody treatments have also been approved by the FDA for treating mild to moderate COVID-19 and they are more successful than molnupiravir at preventing advanced disease. But both remdesivir and the antibody treatments require an intravenous infusion done in a health care setting, making them more complicated and more expensive than just taking a pill at home, which is a decided advantage of molnupiravir. Finally, one of the more effective approved drugs against COVID-19 is the steroid, dexamethasone, but that is only given to very sick patients since its side effects are significant. Therefore, there is much room in the anti-COVID quiver for effective, simple-to-administer drugs such as molnupiravir. Both Pfizer and Roche also have other antiviral drugs that block viral replication in advanced stages of development. Stay tuned.
As of October 5, 2021, the Milken Institute tracker shows that there are 331 “treatments” for COVID-19 in development worldwide. This effort recently got a $3.2 billion boost from the US Antiviral Program for Pandemics, which is a rejuvenated initiative that was started during the MERS outbreak in 2012, but was tabled after MERS fizzled out. Then there is the Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV) program, also sponsored by NIH. These programs focus on developing non-vaccine therapies designed to treat not prevent the disease and they include studies of medicines currently used to treat other diseases (including ivermectin, which has yet to be proven effective) as well as studies of new drugs.
While the news about molnupiravir is encouraging, health experts are concerned that the news also could increase complacency regarding vaccines in the vax-hesitant. It is important to realize that prevention (vaccination) is almost always preferable to treatment (drugs).
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