A global pandemic that's bringing the world to its knees. A big biotech with the first drug to demonstrate clinical efficacy in treating the viral disease. Healthcare experts stating that this drug would likely become the standard of care. Put all of that together and you'd think that the biotech in question would be on the verge of making an enormous amount of money from its antiviral drug.

This scenario is referring to Gilead Sciences (NASDAQ:GILD) and its drug remdesivir. But the last part of the scenario isn't a foregone conclusion. Here are three reasons Gilead's remdesivir might not be the mega-moneymaker that some think it will be.

Magnifying glass over blocks spelling remdesivir

Image source: Getty Images.

1. A unique situation

Gilead Sciences' executive team realizes that they're operating in the spotlight. If the company is perceived as taking advantage of the COVID-19 pandemic to make a massive profit, CEO Dan O'Day will be raked over the coals -- and rightfully so.

O'Day was asked in Gilead's first-quarter conference call if the company's returns on its COVID-19 treatment would be similar to its big returns on other programs targeting HIV and hepatitis C. His response: "We are conscious of the fact that this is unique, and this is different."

Gilead has stated that its "overarching goal is to make remdesivir both accessible and affordable to governments and patients around the world." So far, the company's actions back up that statement. Gilead is donating 1.5 million vials -- its entire supply of the drug through early summer. It recently signed deals with five generic drug makers to supply remdesivir to 127 low- and middle-income countries.

To be sure, Gilead Sciences isn't a charitable organization. It will want to make a profit on remdesivir. But O'Day said in the Q1 call that "we understand our responsibility to a variety of different audiences" in commercializing the drug. The COVID-19 pandemic truly is a unique situation. Don't be surprised if the pricing of remdesivir is relatively low, especially in developing nations.

2. Inherent limitations

The picture many people might have of a COVID-19 treatment is a pill that patients diagnosed with the novel coronavirus disease pop into their mouth and swallow every now and then. But that's not the actual picture for remdesivir.

Gilead's drug is administered intravenously. And, at least for now, the FDA emergency use authorization (EUA) for remdesivir allows the drug to be given only to patients with severe cases of COVID-19 who are hospitalized. The FDA's definition of severe translates to patients with low blood oxygen levels, many of whom will require oxygen therapy or be placed on ventilators.

These limitations shouldn't be overlooked. They certainly whittle down the number of patients who can be treated with remdesivir. It's possible (and perhaps even probable) that other clinical studies will support the use of remdesivir in patients with less severe cases of COVID-19. Gilead is also exploring subcutaneous and inhaled formulations of the drug. But right now, the overall market size for remdesivir is probably smaller than many think it is.

3. Potential rivals

Remdesivir might be on track to become the standard of care in treating COVID-19. But it might not. There are plenty of other potential therapies either already in clinical studies or that soon will be.

Probably the most well-known possible COVID-19 treatment, hydroxychloroquine (HCQ), is currently being evaluated in more than 80 late-stage clinical trials. At least 30 late-stage studies are exploring the potential for convalescent plasma (taken from the blood of patients who have recovered from COVID-19) to treat the novel coronavirus disease. 

Quite a few other big drugmakers are hoping to develop a safe and effective COVID-19 treatment as well. Regeneron plans to begin testing a COVID-19 cocktail therapy in June that could potentially be given before exposure to the novel coronavirus and to treat patients who have already been infected. Alexion's Ultomiris, Incyte's Jakafi, and Roche's Actemra are just three of the other drugs being evaluated in studies targeting COVID-19.

The bottom line is that Gilead could have competition on the way. The more drugs that are successful in clinical studies, the lower the market opportunity could be for remdesivir.

Making money, but not mega-money

Gilead thinks that it could spend $1 billion and perhaps more this year on scaling up its production capacity for remdesivir. The company will need to recover its cost of investment. It's reasonable, therefore, to expect that remdesivir will become a blockbuster drug

But to put things into perspective, Gilead's lineup currently includes three drugs that generated more than $2 billion in sales last year and one that came close to doing so. The company awaits regulatory approval for filgotinib, which could achieve peak annual sales of $4 billion or more.

Remdesivir will likely be a commercial success. But it's not likely to make Gilead the kind of money that the biotech has made and potentially will make with other products.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.