MELISSA BLOCK, HOST:
The FDA has given doctors two new tools for treating patients with COVID-19. The regulatory agency has granted emergency use authorization to drugmakers Pfizer and Merck for their new antiviral therapies. That's good news all by itself. But even better news - it appears the new drugs will work to treat COVID cases that are caused by the omicron variant. Joining us to talk about this is NPR's Joe Palca. And Joe, we're talking about two drugs here. Let's start first with the Pfizer drug. Tell us about it.
JOE PALCA, BYLINE: Yes, it's called Paxlovid or Pax-lovid (ph), if you prefer. It works by messing with a key enzyme in the coronavirus called a protease. If you inhibit the protease, the virus can't grow and spread. You take it with another drug called ritonavir twice a day for five days. The company conducted a study in some 2,200 volunteers that showed that it could reduce the risk of hospitalization and death by close to 90% in people at high risk for the disease. Susanna Naggie is an associate professor of infectious diseases at Duke University Medical Center.
SUSANNA NAGGIE: It does appear to be a highly efficacious oral pill, which we've been waiting on for quite some time.
PALCA: And having a drug that you can give as a pill is a big deal because a doctor could just write a prescription, and the drug could be dispensed by a pharmacy, and the patient could take the pills at home as opposed to going for infusions that are needed for some of the monoclonal antibody therapies for COVID.
BLOCK: OK. So that's the Pfizer drug, Paxlovid. What about the Merck drug?
PALCA: The Merck drug is called molnupiravir, and it received an endorsement for an FDA advisory committee last month. It's also an antiviral. It works by causing errors in the RNA when the virus tries to make copies of itself. It was also tested in a large clinical trial, and the drug does reduce hospitalizations and death, but not nearly as well as Paxlovid. FDA said molnupiravir should only be used when, quote, "other FDA-authorized treatments for COVID-19 are inaccessible or are not clinically appropriate." That seems to be saying, if there's Paxlovid to be had, use that first. FDA didn't authorize molnupiravir for use in patients younger than 18 because the drug may interfere with bone and cartilage growth. The agency also said the medicine is not recommended for use during pregnancy because animal studies suggest that it could harm the fetus.
BLOCK: OK. Now, we mentioned that these drugs appear to work against the omicron variant. If vaccines, as we've heard, are less effective against omicron, why is that not the case with these drugs?
PALCA: Well, vaccines are designed based on the spike protein, and it's the spike protein that has a lot of mutations in omicron. There don't seem to be as many mutations in the genes for the protease protein, and so in theory, these drugs should work against any of the variants. And there are lab tests that suggest that's the case. But of course, to be certain, it will be necessary to test the drug in patients infected with omicron, and those tests haven't been done yet.
BLOCK: Now, you were indicating that Pfizer's drug does seem to be better, more effective than the drug from Merck. So how useful is the Merck drug going to be?
PALCA: Well, it's going to be a question of supply, I think. The Pfizer drug will only be available in the tens of thousands of doses to begin with. A Merck spokesperson said the company will be able to supply 3 million courses of its therapy by the end of January. Susanna Naggie says there will still be patients who will qualify for receiving the Merck drug.
NAGGIE: For the right person, where the risk-benefit favors taking it, I still think it's probably going to be a drug that we see used, at least for now, particularly given the numbers that we're seeing with omicron spreading in various parts of the country.
PALCA: She says any drug that will help keep people out of the hospital is a good thing.
BLOCK: That is NPR's Joe Palca talking about two drugs that have now gotten emergency use authorization from the FDA to fight COVID.
Joe, thanks so much.
PALCA: You're welcome.
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