In this video from Motley Fool Live, recorded on March 29, contributors Brian Orelli and Keith Speights discuss Pfizer's (PFE 0.66%) move beyond vaccines into potential treatments for COVID-19. The pharmaceutical giant is focused on a pair of drug candidates, PF-07304814 and PF-07321332, which could help both early- and late-stage patients on their road to recovery.

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Brian Orelli: Pfizer started a phase 1 study of its protease inhibitor, PF-(a whole bunch of long numbers), but we'll just call it "332" since that's what they end in. Can you talk about what a protease is, and then why inhibiting it might stop the coronavirus from replicating?

Keith Speights: Yeah. So, protease: It's an enzyme. It's a special kind of enzyme that cuts other enzymes, and that's a critical step that's necessary for viral replication. In the case of SARS-CoV-2, which is the virus that causes COVID-19, it starts out as a long protein chain called the polypeptide, and that basically has multiple enzymes linked together. What the protease enzyme does is -- it's like scissors, it cuts those enzymes apart. If it can't do its job, the virus can't replicate, and so that's what these protease inhibitors do: They bind to the proteases, they try to prevent them from doing their cutting job, cutting those enzymes apart. Basically, by doing so, it keeps the virus from replicating.

These inhibitors have been around for quite awhile, for decades really. They've been used for a long time in treating HIV, in treating hepatitis C virus. Now, more recently, in recent years, more effective therapies have come out that captured more of the market for HIV and hepatitis C, but they're still in use. Pfizer is only in its early-stage testing here with targeting COVID-19, but we know that protease inhibitors -- in the past, anyway -- have been both safe and effective, at least in treating other viruses. So I think this is a promising path for Pfizer to take here.

Orelli: Yeah, of course, each individual protease inhibitor works for a specific virus --

Speights: Right.

Orelli: Well, definitely, if we inhibit the protease, Pfizer's drugs [are] going to work. The biggest question is: Well, can it inhibit, in humans, the protease?

Speights: Yeah, there's no guarantee that it's going to work. Again, we're talking about a phase 1 study. There's no guarantee that it's going to work. There could still be some safety issues. But as a class, this particular drug class has a pretty good track record.

Orelli: Yes, definitely. Then also the protease inhibitor, PF-, we'll call this one "814," which is in phase 1b testing for hospitalized patients. Then the other one is for non-hospitalized patients. Any thoughts on which one has better prospects?

Speights: I think it's hard to say. The candidate that's targeting the hospitalized patients with COVID-19 is administered intravenously, so that could tend to be more effective -- IV meds. However, it has a harder job to do because it's battling COVID-19 in patients who are already so sick that they're in the hospital, whereas the oral medication is targeting patients with very early infection. In terms of which one will work better at its intended use, I have no idea, we'll see.

In terms of market potential, this is just my hunch, Brian, but my hunch is that Pfizer might have better commercial prospects with the IV therapy. The reason why is -- again, I'm just speculating here, but -- the widespread availability of COVID vaccines could make people more likely to think that...let's say you've been vaccinated, I just got my second vaccine, and let's say a few weeks from now, I start to have symptoms that could be COVID, but it also just could be a cold or hay fever or something like that. If I've been vaccinated already, I'm going to be more likely to think it's one of the more common things and not COVID, and not even go get treated, so I would never be a candidate to even get the oral medication because I'm assuming that I'm OK.

I think maybe there's going to be a bigger market potential with the IV meds because the people that get sick and get hospitalized, doctors are going to say, "We've got this IV therapy that hopefully works for Pfizer and we'll be more likely to use it." My guess is the IV therapy might have a bigger market potential.

Orelli: Yeah, I agree. I think that also probably they can charge more for the drug for hospitalized patients because you're closer to dying. Therefore, the value of the medication is a lot higher compared to an oral medication, which they're giving to everybody. A lot of those people are going to get better on their own, so the price that they would be able to charge for that is substantially lower.

Speights: Right.