Merck's COVID-19 antiviral pill vs. Pfizer's: What's the same, what's different

Both Merck and Pfizer have recently released data suggesting their COVID-19 antiviral pills are safe and effective ways to treat COVID-19, and if approved, both could be game changers in the fight against the virus. 

Merck's antiviral, which it developed in partership with Miami-based Ridgeback Biotherapeutics, is called molnupiravir. The drugmaker has already filed for emergency use authorization of the drug, saying it cuts the risk of hospitalization or death from COVID-19 by about 50 percent. The FDA's advisory committee is set to meet Nov. 30 to discuss authorizing the drug. 

Pfizer's antiviral is called Paxlovid, and the drugmaker said it cuts the risk of hospitalization or death by 89 percent. The company plans to file for emergency use authorization from the FDA as soon as possible. 

Here's a breakdown of the similarities and differences between the two antivirals: 

What's the same 

Both of the antivirals aim to stop the COVID-19 virus from replicating, and both are given as pills. They were both initially being developed to treat other things but were repurposed to treat COVID-19, NBC News reported. 

For both of the drugs, starting treatment early in the course of the disease is important. The longer the virus has to replicate, the more it spreads and causes damage, NBC News reported. In clinical trials, both Merck's and Pfizer's antivirals were started within five days of the onset of COVID-19 symptoms. 

Both clinical trials reported no adverse side effects. 

What's different 

Though both are antiviral pills, the way they work is different. 

Molnupiravir is a polymerase inhibitor, which works by stopping the virus's genetic material from being replicated accurately, according to NBC News. It tricks the enzyme that replicates the virus's RNA so it inserts errors or mutations, which then get replicated many times until the virus can no longer survive. 

The method is effective, but somewhat risky, NBC News reported, because it could also affect human host enzymes. Katherine Seley-Radtke, PhD, a medical chemist at the University of Maryland-Baltimore County told NBC News that some research suggests drugs similar to molnupiravir can affect other enzymes in the body when given for longer periods of time. 

Paxlovid is made up of two components, an experimental molecule called PF-07321332 and a drug called ritonavir. Both components are protease inhibitors, meaning they block an enzyme that cuts apart long strands of nonfunctional viral proteins into smaller, functional proteins, according to NBC News

The molecule in Paxlovid works on the virus itself, while ritonavir stops other enzymes from destroying it. Ritonavir is also used in some antiviral drugs to treat HIV, NBC News reported. 

 

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