Pfizer (PFE 1.52%) is one of the top pharmaceutical businesses in the world, and it's the undisputed champion of coronavirus medicines. Between its antiviral pill Paxlovid and its vaccine called Comirnaty, it's on track to make around $54 billion in sales of its coronaviral mitigation products before 2022 ends.

And regulators at the Food and Drug Administration (FDA) just gave it a huge and somewhat unexpected gift that could increase that tally by even more. To sweeten the pot, the pharma won't need to spend an additional dime to capture the extra cash, and that's music to investors' ears -- let's investigate what's going on.

Accessing Paxlovid is getting even easier than before

On July 6, regulators at the FDA said that they were expanding the Emergency Use Authorization (EUA) issued for Pfizer's antiviral drug Paxlovid for coronavirus infections so that it could be prescribed by pharmacists. The expanded EUA means that there are fewer barriers for patients seeking treatment, as they don't even need to get a doctor's appointment to get their course of Paxlovid prescribed. While there are a few health-related restrictions that pharmacists will need to abide by when prescribing the medicine, it'll still bring in even more sales for Pfizer. 

That means the company's guidance for $22 billion in Paxlovid sales during 2022 might need to be updated, provided that government purchasers in the U.S. anticipate an increased level of demand or rising utilization of the country's Test to Treat program as a result of the FDA's decision. Results are favorable so far; in the first quarter, the company reported that its U.S. sales of Paxlovid were $1 billion on an operational basis, with an additional $455 million in international sales.

For those keeping track, with the help of Paxlovid's contribution to the pharma's top line, Pfizer currently expects to make between $98 billion and $102 billion for fiscal year 2022. But that sum includes global sales, and the expanded prescribing guidelines are only valid for the U.S., at least unless other regulatory bodies decide to follow in the FDA's footsteps. 

Antiviral competitors will have an even harder time catching up

Aside from the possibility of making additional sales, the new prescribing rules will also help Paxlovid to continue outperforming competing antiviral therapies for coronavirus infections, like Merck's  (MRK 0.16%) pill called molnupiravir and the infusion-delivered remdesivir by Gilead Sciences (GILD 0.23%). Whereas molnupiravir brought in around $952 million in the fourth quarter of 2021 and Merck expects it to make as much as $6 billion this year, Gilead is predicting as much as $2 billion for remdesivir after making $1.4 billion in the last three months of last year.

For Gilead in particular, the new guidelines will be an additional headwind, as its revenue from remdesivir was already declining toward the end of 2021, and its prescribing guidelines are already substantially stricter than those for Paxlovid due to the fact that it's delivered intravenously rather than in the form of a pill. So, it's reasonable to expect that Paxlovid will continue to steal its market share at an even faster rate than before. 

The consequences for Pfizer's stock will be positive, especially if it ends up outperforming its original estimates for the year. Picking up yet another tailwind for Paxlovid sales probably isn't a valid reason to purchase the company's shares on its own, though. Assuming that the pandemic continues to get more and more manageable over time, it's reasonable to expect that sales of antivirals will eventually start to fall, potentially as soon as next year. Until then, Pfizer will remain the top dog in the coronavirus market, and its lead looks to only be increasing.