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The first participants have been dosed in a large Phase 2/3 trial testing a novel oral treatment designed to alleviate symptoms of COVID-19. The first results are expected by the end of this year.

A simple, pill-based COVID-19 treatment that can be taken at home during the earliest stages of infection is perhaps the biggest missing link in the fight against SARS-CoV-2. Over the past 18 months an incredible array of treatments have been developed, from prophylactic vaccines to monoclonal antibodies preventing serious disease.

But while vaccines can help reduce a person’s risk of hospitalization or death, and other therapies can be administered while in hospital to prevent serious decline, there is a vital need for an effective oral treatment that can be taken at home in the very earliest stages of disease. A number of anti-COVID-19 pills are currently in development, but Pfizer’s candidate is one of the first oral antivirals designed specifically to target SARS-CoV-2 to reach advanced human trial stages.

Called PF-07321332, the drug is in a class of antiviral agents known as protease inhibitors. Proteases are enzymes crucial to viral replication mechanisms and protease inhibitors have previously been developed to treat HIV/AIDS and hepatitis C.

“Protease inhibitors, like PF-07321332, are designed to block the activity of the main protease enzyme that the coronavirus needs to replicate,” Pfizer explains in a recent statement. “Co-administration with a low dose of ritonavir is expected to help slow the metabolism, or breakdown, of PF-07321332 in order for it to remain in the body for longer periods of time at higher concentrations, thereby working continuously to help combat the virus. Ritonavir has previously been used in combination with other antivirals to similarly inhibit metabolism.”

Two double-blind, placebo-controlled Phase 2/3 clinical trials are currently underway testing the oral PF-07321332/ritonavir combination. The first trial commenced in July looking at whether a course of the drug administered to those at high-risk of severe COVID-19 would reduce rates of hospitalization and death. Over the next few months 3,000 people are expected to be enrolled.

The second trial commenced in late August and is investigating the effects of the drug on individuals at a low-risk of severe COVID-19. Unlike the other trial, which is focusing on preventing hospitalization and death, here the researchers are looking at whether PF-07321332 shortens the duration and severity of COVID-19 symptoms in generally healthy adults.

This trial is planning to enroll 1,140 participants. The at-home treatment begins within three days of COVID-19 symptoms appearing and involves taking a pill every 12 hours for five days. Pfizer expects preliminary results for PF-07321332 by the end of the year.

Source: Pfizer