UK to roll out COVID-19 antiviral drug trial this month

Britain will start to roll out Merck’s molnupiravir Covid-19 antiviral pill through a drug trial later this month, Susan Hopkins, Chief Medical Adviser at the UK Health Security Agency said on Sunday.

The government said in October it had secured 480,000 courses of the Merck drug, as well as 250,000 courses of an antiviral pill developed by Pfizer Inc.

Asked about the molnupiravir approval, Hopkins told BBC television: “That is great news and it will start to be rolled out through a drug trial in the end of this month/the beginning of December.”

Hopkins said all the trials so far had been done with the unvaccinated, so this would help understand how it will work in the wider vaccinated population.

“The new Pfizer drug is probably not going to be licensed until the new year some time,” she added. “It is still likely to be a couple of months away.”

Pfizer and Merck have developed experimental antiviral pills that have shown promising efficacy in trials of adults with COVID-19 who are at high risk of serious illness.

Both drugs also are being studied to see if they can prevent infection in people exposed to the virus.

Here is an explanation of the differences in the two pills.

Which of the new pills works better?

Trial figures provided by the two companies suggest that Pfizer has the more effective pill, but they have not yet offered full data.

Pfizer said on Friday trial results showed that its pill reduced the chance of hospitalization or death by 89% in COVID-19 patients at risk for severe illness given the treatment within three days of the onset of symptoms and by 85% when given within five days of onset.

Merck on Oct. 1 said its pill lowered the chance of hospitalization or death by about 50% in patients at risk for severe illness given the treatment within five days of onset. It did not provide figures regarding patients getting the pill within three days of onset.

Pfizer’s drug has the brand name Paxlovid. Merck’s drug has the brand name Lavgevrio in Britain, where it has won regulatory approval.

How do they work?

Both drugs are given for five days. Pfizer’s regimen is three pills in the morning and three pills at night. Merck’s drug is taken as four pills in the morning and four at night.

Pfizer’s drug is part of a class known as protease inhibitors designed to block an enzyme that the coronavirus needs to multiply. Pfizer said that because the drug targets a part of the virus essential to replication, the pathogen cannot become resistant to the treatment.

Pfizer’s drug is given in combination with ritonavir, an older antiviral that boosts the activity of protease inhibitors but can cause gastrointestinal side effects and interfere with other medications.

Merck’s pill, developed with Ridgeback Biotherapeutics, is a nucleoside analogue with a mechanism of action that aims to introduce errors into the genetic code of the virus. Because the drug generates random mutations into the virus, it is difficult for the coronavirus to evolve and become resistant.