First at-home COVID-19 antiviral prescription drug authorized by Health Canada

OTTAWA —
Health Canada has authorized the use of Pfizer’s COVID-19 antiviral treatment Paxlovid, the first oral and at-home prescription medication to be cleared for use in this country.

The federal health agency says the prescription-only medication can be given to adults ages 18 and older to treat mild to moderate cases of COVID-19, if they have a confirmed positive test and are at a high risk of becoming seriously ill. 

The authorization comes with specific instructions on scenarios in which the regime cannot be used, including to prevent COVID-19 infections or to treat patients who are already hospitalized due to severe COVID-19 cases.

The medication— two antiviral medicines co-packaged together— cannot be taken for longer than five days in a row, nor can it be given to teens or children.

“The authorization today provides a new tool the toolkit against COVID-19 at a crucial time the pandemic as we’re faced with new variants. Importantly, it is a more accessible antiviral treatment for those at high risk of progression to severe COVID-19,” said Health Canada’s Chief Medical Adviser Dr. Supriya Sharma, during a technical briefing discussing Paxlovid’s authorization.

“No drug, including Paxlovid, is a substitute for vaccination,” she said..

Pfizer submitted clinical data for the oral medication, on Dec. 1, 2021. 

The government has a deal in place with the pharmaceutical giant securing access to an initial one million doses of the therapeutic drug.

Responding to recent calls from the provinces for a swift rollout of this medication in the face of an expected surge in Omicron hospitalizations, the federal government has vowed that delivery of the drug will happen in short order.

Health Minister Jean-Yves Duclos and Procurement Minister Filomena Tassi will be holding a press conference to discuss the rollout of this treatment at 1:30 p.m. EST.

“While there is currently limited global supply of Paxlovid, we are working to firm up a delivery schedule with the intent of bringing treatment courses to Canada as quickly as possible,” said Chief Public Health Officer Dr. Theresa Tam during the technical briefing.

She said based on this, the Public Health Agency of Canada has communicated to the provinces and territories an interim set of guidelines for use of this new treatment while supplies are limited.

This means that provinces are being asked to prioritize giving this medication to:

• Individuals who have the highest likelihood of severe illness including those who are immunocompromised regardless of vaccination status;
• Individuals over the age of 80 whose vaccinations are not up to date; and
• Canadians aged 60 or older who live in underserved rural or remote communities, long-term care homes, who are from First Nations, Inuit, and Metis communities, or whose vaccinations are not up to date.

As well, first use should be prioritized for those whose infections have been confirmed and are able to start the treatment within five days of symptom onset. Tam said that if PCR testing is not available, or if results will not be available until more than five days from symptom onset, a rapid antigen test may be used.

EFFICACY AND SIDE EFFECTS  

In November 2021, Pfizer released the results of their Phase 2/3 trials for the drug, stating that they had found the pills to significantly reduce hospitalization and death in COVID-19 patients. 

Pfizer said that in a randomized, double-blind study of more than 380 patients, there was an 89 per cent reduction in the risk of being hospitalized or dying of COVID-19 in patients that received Pfizer’s pill within three days of displaying COVID-19 symptoms, compared to the study group that received a placebo.

The drug giant has been submitting data to Health Canada on a rolling basis, with new information recently submitted showing its efficacy against the Omicron variant, with more data expected in the months ahead, said Sharma.

According to Pfizer, Paxlovid is designed to block the activity of an enzyme in SARS-CoV-2 that is essential for the virus to replicate itself, and also help to slow the breakdown of the pill’s ingredients in order to help combat the virus for longer.

“PAXLOVID stops the virus from multiplying. This can help your body to overcome the virus infection and may help you get better faster,” reads Health Canada’s authorization.

Paxlovid contains two medicines co-packaged together, a 150mg pink tablet of Nirmatrelvir and a 100mg white tablet of Ritonavir, which has been used in combination with other antiviral medications before.

The regime is meant to be taken consistently twice a day, for five days in a row. The agency has outlined on their website the detailed instructions for taking this medication, as well as a list of potential contraindications.

For example, Health Canada has issued warnings for patients with kidney or liver problems; patients with a human immunodeficiency virus (HIV) infection; patients who are pregnant, breastfeeding, or are planning to become pregnant; and patients who take a series of other commonly-used medicines which may interact with Paxlovid causing decreased drug effectiveness, or in some cases cause potentially serious effects.

Side effects can include an altered sense of taste, diarrhea, muscle pain, vomiting, high blood pressure, and headache. Though, given the limited use of this medication to date, the agency cautions that it is possible not all side effects are known at this time and advise speaking with a healthcare professional if other side “troublesome” effects arise.

“Health Canada’s review determined that the benefits pf Paxlovid outweigh its potential risks, but it’s important to remember that inherently all drugs carry some risks, and this is no different,” said Sharma.

“As a prescription medication, patients need to discuss the risks and benefits of treatment with the healthcare provider who’s aware of their health conditions and other medications.”

MERCK DRUG REVIEW ONGOING

Health Canada has also been reviewing an experimental pill from drugmaker Merck, called molnupiravir, since mid August.

The federal government has a contract to purchase 500,000 of Merck’s antiviral medication, with an option for 500,000 more pending regulatory approval.

In late December, the U.S. Food and Drug Administration issued an emergency use authorization for both Pfizer and Merck’s drugs. 

With files from CTV News’ Alexandra Mae Jones and Sarah Turnbull