Health Canada still reviewing data on antiviral COVID-19 drug approved in U.K.

Health Canada says it's still reviewing data on an antiviral COVID-19 drug that was authorized Thursday in the United Kingdom.

The federal regulator said it continues to receive data "as new information becomes available" from pharmaceutical company Merck on their drug molnupiravir, considered the first pill to successfully treat COVID-19.

It offered no timeline for completion of the review process.

"As the review is still ongoing, it is not possible to predict when a regulatory decision will be made," Health Canada stated by email.

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While molnupiravir was granted conditional authorization for use in Britain, it wasn't immediately clear how quickly the pill would be available there.

Merck has been supplying data to Health Canada on a rolling basis since August, when the product was still undergoing clinical trials.

Health Canada said earlier Thursday by email that it was "awaiting the final package of manufacturing data" from Merck, but said later in the day that statement was issued in error, however did not immediately elaborate.

The regulator said its review will determine whether benefits of using the drug outweigh risks and ensure it meets "stringent safety, efficacy and quality requirements."

Merck announced preliminary results in September showing its drug cut hospitalizations and deaths by half among patients with early COVID-19 symptoms. The results haven't yet been peer reviewed or published in a scientific journal.

The company also didn't disclose details on molnupiravir's side effects, except to say that rates of those problems were similar between people who got the drug and those who received dummy pills.

Molnupiravir was initially studied as a potential flu therapy with funding from the U.S. government. Last year, researchers at Emory University in Atlanta, Ga., decided to repurpose the drug as a potential COVID-19 treatment. They then licensed the drug to Ridgeback and partner Merck.

The drug targets an enzyme the coronavirus uses to reproduce itself, inserting errors into its genetic code that slow its ability to spread and take over human cells. That genetic activity has led some independent experts to question whether the drug could potentially cause mutations leading to birth defects or tumours.

Britain's Medicines and Healthcare products Regulatory Agency said molnupiravir's ability to interact with DNA and cause mutations had been studied "extensively" and that it wasn't found to pose a risk to humans.

Dr. Sumon Chakrabarti, an infectious disease expert in Mississauga, Ont., said molnupiravir is intriguing because the errors it inserts into the genetic code aren't recognized as errors by the SARS-CoV-2 virus.

"So that lead to massive mutations and the virus dies," he said. "It's kind of cool, actually."

Merck Canada said Thursday that Health Canada will decide on authorization after reviewing "all necessary evidence."

The company added that a supply agreement was not yet in place but that conversations with the Canadian government were ongoing.

"We remain committed to working with the government to ensure Canadians will have access to our medicine should it receive market authorization by Health Canada," Merck said in an email from its media centre.

Chakrabarti said the current context of COVID-19's circulation in the United Kingdom, where there's been a "slow burn of a ton of hospitalizations," may have provided more urgency for regulators there to authorize the drug on a conditional basis.

He said Health Canada will consider use of the drug "in the Canadian context."

"They've been pretty good about not rushing things," he said of the Canadian regulator. "They look at the data and when they make a recommendation, you can trust it."

Molnupiravir is also pending review with regulators in the United States, the European Union and elsewhere. The U.S. Food and Drug Administration announced last month it would convene a panel of independent experts to scrutinize the pill's safety and effectiveness in late November.

Merck and partner Ridgeback Biotherapeutic have requested clearance for the drug for adults with early cases of COVID-19 who are at risk for severe disease or hospitalization.

The pill, a take-home treatment, was licensed in Britain for adults 18 and older who have tested positive for COVID-19 and have at least one risk factor for developing severe disease, such as obesity or heart disease. Patients with mild-to-moderate COVID-19 would take four pills of the drug twice a day for five days.

Chakrabarti, who hasn't seen the clinical trial data, said the caveat with the drug is that it has to be taken early — either shortly after exposure or in the first days of infection.

"The absolute risk reduction doesn't seem to be that high, but at least it's another tool in the box," he said. "Anything we can use to to prevent hospitalization is good."

With files from The Associated Press