New York,  US pharmaceutical company Pfizer has begun Phase 1 clinical trial of a novel oral antiviral drug for SARS-CoV-2, the virus that causes Covid-19.

The oral antiviral clinical candidate "PF-07321332", a SARS-CoV2-3CL protease inhibitor, has demonstrated potent in vitro anti-viral activity against SARS-CoV-2, as well as activity against other coronaviruses, the company said in a statement late on Tuesday.

According to the company, the findings suggest potential for use in the treatment of Covid-19 as well as potential use to address future coronavirus threats.

"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 hospitalised or in critical care," said Mikael Dolsten, Chief Scientific Officer and President, Worldwide Research, Development and Medical of Pfizer.

"At the same time, Pfizer's intravenous anti-viral candidate is a potential novel treatment option for hospitalised patients. Together, the two have the potential to create an end-to-end treatment paradigm that complements vaccination in cases where the disease still occurs," Dolsten added.

Protease inhibitors bind to a viral enzyme (called a protease), preventing the virus from replicating in the cell. Protease inhibitors have been effective at treating other viral pathogens such as HIV and hepatitis C virus, both alone and in combination with other anti-virals, the company said.

Currently marketed therapeutics that target viral proteases are not generally associated with toxicity and as such, this class of molecules may potentially provide well-tolerated treatments against Covid-19, it added.

The Phase 1 trial is a randomised, double-blind, sponsor-open, placebo-controlled, single and multiple dose-escalation study in healthy adults evaluating the safety, tolerability and pharmacokinetics of PF-07321332.

The initiation of this study is supported by preclinical studies that demonstrated the antiviral activity of this potential first-in-class SARS-CoV-2 therapeutic designed specifically to inhibit replication of the SARS-CoV2 virus.

The structure of PF-07321332, together with the pre-clinical data, will be shared in a Covid-19 session of the Spring American Chemical Society meeting on April 6.

The company said that it is also investigating an intravenously administered investigational protease inhibitor, PF-07304814, which is currently in Phase 1b multi-dose trial in hospitalised clinical trial participants with Covid-19.