Pfizer (PFE  ) announced on Tuesday that it has started an early stage clinical trial for the U.S. pharmaceutical giant's experimental antiviral drug for the potential treatment of COVID-19 and other future coronaviruses. The treatment candidate is administered orally.

The company's Phase one trial of the drug--known as PF-07321332--will be conducted in the United States, with healthy adult participants to evaluate the potential treatment's safety and tolerability profiles. The placebo-controlled study will research the drug's effects in both single and multiple dose regimens.

The drug is a protease inhibitor, which works by blocking a virus's ability to replicate in human cells by inhibiting a critical enzyme. This class of drugs are used in the treatment of HIV and hepatitis C by stopping the viral life cycle of those infectious diseases.

"Tackling the COVID-19 pandemic requires both prevention via vaccine and targeted treatment for those who contract the virus," said Mikael Dolsten, Pfizer's chief scientific officer, in a press release. "Given the way that SARS-CoV-2 is mutating and the continued global impact of COVID-19, it appears likely that it will be critical to have access to therapeutic options both now and beyond the pandemic."

Since the drug is taken by mouth, it has the potential to be used outside of a healthcare setting for newly infected individuals, and possibly curbing the risk of severe disease or hospitalization.

The new trial comes alongside another early-stage study of an intravenously administered protease inhibitor developed by Pfizer, called PF-07304814. That drug is currently in Phase 1b clinical trials of patients hospitalized with COVID-19.

"We have designed PF-07321332 as a potential oral therapy that could be prescribed at the first sign of infection, without requiring that patients are hospitalized or in critical care," Dolsten continued. "At the same time, Pfizer's intravenous antiviral candidate is a potential novel treatment option for hospitalized patients. Together, the two have the potential to create an end to end treatment paradigm that complements vaccination in cases where disease still occurs."

Pfizer has also developed a COVID-19 vaccine with German biotech BioNTech (BNTX  ), which is authorized for emergency use in several nations including the United States and the European Union.