Is Merck's Dig at Pfizer's COVID-19 Pill Justified?

Merck (MRK 0.35%) and Pfizer (PFE -0.08%) could soon compete against each other in the oral COVID-19 therapy market. But Merck has already started a war of words with Pfizer even before either drug has won authorization. In this Motley Fool Live video recorded on Dec. 8, Motley Fool contributors Keith Speights and Brian Orelli discuss whether or not Merck's recent dig at Pfizer's COVID-19 pill is justified.

Keith Speights: All right, Brian, let's stay on COVID-19, but we're going to move to a different angle. This isn't about vaccines, this is about COVID-19 pills, the oral therapies.

There has been some sniping back and forth between Merck and Pfizer. Both companies of course have developed COVID-19 pills. Merck Senior Vice President of Global Medical Affairs, Eliav Barr, told the Financial Times that Pfizer's COVID-19 pill would be unsuitable for some patients because of the anti-HIV drug, ritonavir, that's included in the regimen for Pfizer's oral COVID therapy Paxlovid.

Then Pfizer fired back. Pfizer said Paxlovid is safe and that any potential drug-drug interactions could be managed by adjusting the dosing.

Do you think that the potential for these drug interactions could hurt Pfizer's COVID pill sales, or is this just more of a case where Merck is maybe engaging in some trash talk here?

Brian Orelli: Can I claim neutral Switzerland on this one? Because [laughs] they're both right. Ritonavir is in Pfizer's Paxlovid. What it does is, it's not actually an active drug, it doesn't do anything to the virus. It doesn't do anything to the HIV, virus either.

What it does is it inactivates human protein that is responsible for breaking down the active ingredient in Pfizer's Paxlovid and does the exact same thing in HIV drugs. By keeping it from getting degraded, then it has a longer half life and can be more active. Ritonavir also inhibits the degradation of hundreds of other drugs.

If you're taking a drug, let's say generic Lipitor, I think that's one of the ones that gets broken down less if you take ritonavir and then start taking Paxlovid. Now you're taking effectively a much larger dose of Lipitor because it's not getting broken down as quickly and so it's building up in your bloodstream. Some of these drugs could actually be deadly at high doses if you're taking ritonavir.

The solution is either to stop taking the medication if that's possible. Not taking a Lipitor for 10 days isn't going to have any major effect on your health. Or you could take a lower dose of the drug if it's been established what the lower dose should be if you're on ritonavir, or you could just take a different antiviral and that's what Merck would love you to do.

The HIV doctors who have been dealing with this for years have said ritonavir is a big part of many of the regimens. But most primary care doctors probably have little or no experience with ritonavir, and presumably, pharmacists could catch the drug-drug interaction, but only if the pharmacy has all the prescriptions of the patient.

If you go into different pharmacies then they're not going to necessarily know other drugs that you're currently on. Obviously, the pharmacist could ask the patient, "What are your any other medications?" Because this is has drug-drug interactions.

But you would imagine that most people are going to have somebody else go pick up their COVID-19 treatment since they currently have active COVID-19. That may make things challenging because does your wife or your friend know all drug names of the drugs that you're on? I guess you can just call them now that we have cellphones.

Maybe it's not a horrible issue, but it's definitely something that needs to be managed very closely. I think it's an issue, but it's a manageable issue.