Pfizer Inc (NYSE: PFE) has started an early-stage U.S. trial of an oral COVID-19 antiviral therapy, dubbed as PF-07321332.

• The drugmaker, which developed the first authorized COVID-19 vaccine in the U.S. with Germany's BioNTech SE (NASDAQ: BNTX), said the antiviral candidate showed potent activity against SARS-CoV-2 in lab studies.
• The Phase 1 study progressed to multiple ascending doses after completing the dosing of single ascending doses in healthy adults.
• PF-07321332 is a protease inhibitor that prevents the virus from replicating in cells.
• The company is also studying an intravenously administered antiviral candidate in an early-stage trial in hospitalized COVID-19 patients.
• Pfizer's candidate is behind two other oral antiviral therapies, which are in mid-stage trials:
  •  Molnupiravir - in development by Merck & Co (NYSE: MRK) with Ridgeback Bio. Recent interim data showed that the antiviral significantly reduced the infectious virus in COVID-19 patients after five treatment days.
  • Roche Holdings AG (OTC:RHHBY) and Atea Pharmaceuticals Inc (NASDAQ: AVIR) are developing AT-527 in mild or moderate COVID-19 patients in an outpatient setting. The first patient was dosed in February. 
• Gilead Sciences' remdesivir is currently the only FDA-approved drug for the treatment of COVID-19.
• The FDA granted an emergency authorization to intravenous therapies from Eli Lilly bamlanivimab alone and in combination with etesevimab, and a combination therapy from Regeneron.
• Price Action: PFE shares are trading 0.97% lower at $35.65 in market hours on the last check Tuesday.