Pfizer, Merck launch new trials of oral antiviral drugs for COVID

Pfizer said its latest mid-to-late-stage trial will enroll 1,140 non-hospitalized adults diagnosed with coronavirus infection who are not at risk of severe illness. Patients in the trial will be given Pfizer's pill, known as PF-07321332, and a low dose of ritonavir, an older medication widely used in combination treatments for HIV infection.

Pfizer's drug is designed to block the activity of a key enzyme that is needed for the coronavirus to multiply.

Merck said its new trial will study experimental drug molnupiravir for the prevention of COVID-19 among adults in the same household as someone diagnosed with symptomatic coronavirus infection. Merck and partner Ridgeback Biotherapeutics are already conducting a late-stage trial of the treatment in non-hospitalized patients to see if it reduces the risk of hospitalization or death.

Molnupiravir is a type of antiviral designed to introduce errors into the RNA of the virus that eventually prevent it from replicating.

Pfizer began in July a different trial of PF-07321332 in adults with COVID-19 infection who are at high risk of becoming severely ill due to underlying health conditions such as diabetes. The company said it expects initial results from that study some time this fall.

Rivals Pfizer and Merck, along with Swiss pharmaceutical Roche Holding AG, have made the most progress in developing what would be the first antiviral pill to treat, or possibly prevent, COVID-19.

To date, Gilead Sciences Inc's intravenous drug Veklury, known generically as remdesivir, is the only approved antiviral treatment for COVID-19 in the United States.

Roche and partner Atea Pharmaceuticals in June said early data from a trial of their experimental oral antiviral AT-527 showed that it lowered viral load in hospitalized patients.

Merck said in June that the U.S. government agreed to pay about $1.2 billion for 1.7 million courses of molnupiravir, if it is proven to work and authorized by regulators. The company said it expected to file for U.S. emergency use authorization of molnupiravir in the second half of 2021 at the earliest.

Pfizer said in July if the PF-07321332 trial was successful, it would file for a potential emergency use authorization in the fourth quarter.