Though much attention has been paid to the development of a coronavirus vaccine in the past weeks, companies that are focused on treatments are also making rapid progress. Regeneron Pharmaceuticals (NASDAQ:REGN) is working on two efforts: an antibody cocktail and the repurposing of a rheumatoid arthritis drug that it commercializes with partner Sanofi (NASDAQ:SNY). As for Gilead Sciences (NASDAQ:GILD), the U.S. Food and Drug Administration (FDA) recently granted the company emergency use authorization for its coronavirus treatment.

Beyond the coronavirus programs, both companies have full pipelines and product portfolios. The question is: If you are looking to add just one coronavirus stock to your holdings, should you choose Regeneron or Gilead?

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The case for Regeneron

Unlike Gilead, Regeneron doesn't have a coronavirus treatment that is in use beyond clinical trials, though the company is moving forward rapidly. After identifying hundreds of virus-neutralizing antibodies, Regeneron chose two for a "cocktail" that just entered clinical testing this month. The candidate is being developed to both treat and prevent infection. The trial includes four test groups: hospitalized COVID-19 patients, non-hospitalized COVID-19 patients, uninfected people with exposure to a COVID-19 patient, and uninfected people at high risk of exposure, such as healthcare workers. 

Regeneron's second coronavirus effort involves testing rheumatoid arthritis drug Kevzara in severe and critical coronavirus patients. Kevzara works by inhibiting the interleukin-6 pathway. Interleukins are a type of protein that regulate inflammatory response. Trial data showed no benefit in severe patients but potential benefit in critical patients, so Regeneron is continuing Kevzara phase 2/3 studies with critical patients only.

Regeneron also offers plenty of growth outside of the coronavirus program. Annual revenue has been climbing for more than a decade. Cancer treatment Libtayo and eye drug Eylea may keep that trend going.

In treating advanced cutaneous squamous cell carcinoma, a form of skin cancer, Libtayo posted a 179% surge in sales to $75 million in the first quarter. And the company stopped a phase 3 trial for Libtayo in first-line non-small cell lung cancer early after a positive overall survival benefit was reached. The company is planning on regulatory submissions for that indication later in the year. Regeneron also plans to submit Libtayo for approval in second-line advanced basal cell carcinoma this year after positive pivotal trial data in that indication.

Though Eylea's annual growth rate of 6% wasn't steep, first-quarter sales of the treatment for wet age-related macular degeneration totaled $1.9 billion. And the growing market means more opportunity ahead. The global market for the disorder is expected to grow at a compound annual rate of 7.1% to reach $10.4 billion by 2024, a report from Prescient & Strategic Intelligence showed. 

The case for Gilead

Gilead is giving away its total existing supply of remdesivir, or about 1.5 million individual doses of the potential coronavirus treatment. The main question now is how much revenue remdesivir may generate. Gilead hasn't yet set a price for the drug, and since management plans to invest as much as $1 billion in remdesivir this year, pricing will be crucial. Given that remdesivir is a treatment for a pandemic, developed to some extent with government money, Gilead's challenge will be to make an acceptable profit while still maintaining affordability for patients.

While remdesivir hasn't been a miracle cure, the drug has demonstrated enough benefit to drive demand. Patients taking remdesivir for five days were 65% more likely to show clinical improvement on day 11 than those in a standard-of-care group, according to recent phase 3 trial data.

Gilead has nearly 50 additional drug candidates in the pipeline and almost 30 commercialized products in areas including HIV, oncology, and cardiovascular disease. The strongest element here is Gilead's HIV business. Sales of Biktarvy more than doubled to nearly $1.7 billion in the first quarter compared with the year-earlier period, leading gains in the overall program. The global HIV drug market is expected to grow at a compound annual rate of 3.7% to reach $26 billion by 2022, according to Allied Market Research.

While the HIV business represents an opportunity, sales of Gilead's chronic hepatitis C drugs have been on the decline, and that's weighed on annual revenue growth. Former blockbuster Sovaldi generated $10 billion in revenue back in 2014, but that has plummeted into the millions due to competition and bargaining with payers.

More growth is ahead for Gilead, though, as the company awaits regulatory decisions on filgotinib for rheumatoid arthritis. FDA approval may come as early as this month, since Gilead submitted  the drug for priority review in December. The company is preparing for a possible launch in the second half of 2020 and is aiming for approval in Japan and Europe later this year.

Regeneron or Gilead?

Both biotech companies make solid investments -- for their coronavirus work and their product portfolios. And both have possible product launches on the horizon. Right now, though, Gilead represents a better buy because it is close to generating revenue from its coronavirus treatment and regulatory approval for filgotinib may be right around the corner.

Though Regeneron has shown more revenue growth momentum than Gilead in recent years, filgotinib for rheumatoid arthritis and other indications in phase 2 and phase 3 studies may be a ticket to growth. On its full-year 2019 earnings call, Gilead mentioned the possibility of five filgotinib indication launches in the next four years. Now may be a good time to bet on all of that potential.

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.