Paxlovid (Nirmatrelvir and Ritonavir): Uses, Dosage, Side Effects and Cost in Canada

Paxlovid is a prescription COVID-19 antiviral made by Pfizer. It is a pack of two medicines: nirmatrelvir, which acts against the virus, and ritonavir, which keeps nirmatrelvir at a useful level in the body.

Health Canada has authorized Paxlovid for mild-to-moderate COVID-19 in adults with a positive test who are at high risk of becoming severely ill. It must be started as soon as possible after diagnosis and within 5 days of the first symptoms. It is not for people in hospital with severe COVID-19, and it is not used to prevent COVID-19.

In BC, Paxlovid is prescribed for adults who are moderately to severely immunocompromised, or who are 60 or older with at least one high-risk health condition. Most people in BC do not need it.

Paxlovid needs a prescription. BC residents can speak with a BC-licensed doctor by phone through Avee Health to ask whether it is appropriate for them. The doctor decides based on your health history and your other medicines. A prescription is not guaranteed.

In Canada, Paxlovid is authorized for:

• Treating mild-to-moderate COVID-19 in adults with a positive test who are at high risk of becoming severely ill, including a risk of hospitalization or death

Paxlovid is not authorized for people who need hospital care for severe or critical COVID-19, to prevent COVID-19 before or after an exposure, or for more than 5 days in a row. Its safety and effectiveness have not been established in people under 18.

In BC, Paxlovid is prescribed for adults who are moderately to severely immunocompromised, or who are 60 or older with at least one high-risk health condition. A second course is not given if symptoms continue after the 5 days. Eligibility rules change, so check the BC government's Paxlovid page or ask your doctor or pharmacist.

Nirmatrelvir blocks an enzyme the COVID-19 virus needs to copy itself. Ritonavir slows the breakdown of nirmatrelvir by a liver enzyme called CYP3A, so it stays active longer. The same effect on CYP3A is why Paxlovid interacts with so many other medicines.

In the main clinical trial, in high-risk adults who were not in hospital, fewer people given Paxlovid were hospitalized or died than people given placebo.

Your doctor sets your dose. The usual directions in the Canadian product monograph are:

• Usual dose: two 150 mg nirmatrelvir tablets and one 100 mg ritonavir tablet, taken together, twice a day for 5 days.
• When to start: as soon as possible after COVID-19 is diagnosed, and within 5 days of the first symptoms.
• Moderate kidney problems: one 150 mg nirmatrelvir tablet and one 100 mg ritonavir tablet, taken together, twice a day for 5 days.

Paxlovid is not recommended for people with severe kidney problems or severe liver problems. Tell your doctor about any kidney or liver disease.

How to take it: with or without food. Swallow the tablets whole. Do not chew, break or crush them. Take the full 5 days unless your doctor tells you to stop.

Missed dose: if you are less than 8 hours late, take it as soon as you remember and carry on as usual. If you are more than 8 hours late, skip the missed dose and take the next one at the usual time. Do not take a double dose.