Professor Kelly Grindrod answers questions about Pfizer’s COVID-19 antiviral treatment Paxlovid
Health Canada has approved Pfizer’s Paxlovid as the first oral and at-home prescription medication to treat COVID-19 in Canada.
Kelly Grindrod, a pharmacist and University of Waterloo professor, answers common questions about this new drug.
Does Canada have any of this medication yet?
Canada signed an agreement with Pfizer to secure one million treatment courses of Paxlovid. To date, Canada has received 30,400 treatment courses, with another 120,000 expected before the end of March. Ontario has received 11,000 doses which have been shipped across the province.
How does Paxlovid work?
Paxlovid is a combination of two drugs. The main ingredient is nirmatrelvir, which works by stopping the SARS-CoV-2 virus that causes COVID from replicating in the body. Nirmatrelvir works very well, but the body breaks it down very quickly. Thus, Paxlovid also includes a drug called ritonavir, which is added to work as an enzyme blocker to slow the body’s ability to break down nirmatrelvir. It helps boost nirmatrelvir to have a stronger, longer-lasting effect.
Paxlovid is indicated for use in mild illness before someone is sick enough to need hospital care. It aims to prevent a mild infection from becoming a severe infection. People with severe illness are offered different treatments.
Can anyone get Paxlovid from a family doctor? Or will it primarily be used in hospitals?
Paxlovid is not yet available from family doctors. Right now, Paxlovid is only available from a small number of COVID-19 Clinical Assessment Centres located throughout the province. Family doctors can help refer patients to these centres too. Eventually, Paxlovid may be made available through family doctors and pharmacies.
To take Paxlovid, you need to have tested positive within the last five days, and the COVID test needs to be either a PCR test or a healthcare provider administered rapid test.
Because Paxlovid contains ritonavir as a boosting agent, it has very serious drug interactions with many other medications. This makes it very complicated to prescribe.
There is more information on the Government of Ontario website.
Is Paxlovid a new medication? Is it effective and safe?
Nirmatrelvir is a new drug that has only been approved for use in COVID-19. Ritonavir is an older drug that has been used for many years to help boost other medications used in the treatment of HIV and hepatitis C.
Health Canada has reviewed the data from Pfizer and approved the use of Paxlovid based on interim results of the EPIC-HR trial. EPIC-HR included more than 2,000 people who had developed mild COVID symptoms and tested positive for COVID within the last five days, but who were not sick enough to need supplemental oxygen or hospital care.
The trial results have not been published yet, though Health Canada reviewed the EPIC-HR interim study data during the approval process. The product monograph notes that Paxlovid reduces the risk of severe illness and death by 89 per cent.
Side effects appear to be generally mild. Out of every 100 people who take the drug, five may experience an altered sense of taste, three will have diarrhea, one will vomit, one will have a temporary increase in blood pressure, one will have a headache, and one will have muscle aches. Most will have no side effects.
Does COVID-19 vaccination status affect someone’s ability to take Paxlovid?
Like with vaccination, one of the goals of using Paxlovid is to lessen the impact of COVID-19 on our healthcare system. As long as Canada has a limited supply of Paxlovid, it will likely be prioritized for the people most likely to need hospital care. That includes people who are older and who may be either unvaccinated, have a serious health condition, or have a moderate to severely weakened immune system. However, as we get more Paxlovid supply and more experience with the drug, it may become more widely available.
