Doctors across Canada are now assessing COVID patients to determine which ones may be candidates for Pfizer’s antiviral medication, Paxlovid.

The drug was approved by Health Canada a few weeks ago but it’s hard to even imagine who might actually get the pills when they have so many potential contraindications and dangerous interactions with other medications.

The antiviral pills must be taken within five days of infection with COVID. Only the highest risk patients (unvaccinated or immunocompromised, those with diseased organs, others with obesity, diabetes, or neurological conditions, etc.) are going to be considered for Paxlovid. The medication was shown in Pfizer clinical trials to drastically reduce the need for hospitalization but clinical trials aren’t real-world experiences.

By March, the federal government expects to have 120,000 doses shipped to provinces; to date, 30,000 have been shipped across Canada. Here in B.C., health authorities have just released instructions to physicians about how to screen patients who may be candidates for the pills.

Health Canada deemed that the benefits of Paxlovid outweigh its risks while at the same time conceding that the treatment “has the potential to interact with a number of other drugs, potentially decreasing its effectiveness or in some cases causing potentially serious effects.”

The drug interactions could cause severe, life-threatening effects, or even death. Those who are taking other medications could find that they don’t get much of a benefit from Paxlovid.

These are the medications that could have bad interactions with Paxlovid:

  • alfuzosin, used for benign prostatic hypertrophy
  • amiodarone, bepridil*, dronedarone, flecainide, propafenone and quinidine, used to treat arrythmias
  • apalutamide, used in prostate cancer treatment
  • astemizole* or terfenadine* for allergy symptoms
  • cisapride* for stomach disorders
  • colchicine, to treat gout in patients with kidney or liver problems
  • ergotamine*, dihydroergotamine (for headaches), ergonovine, methylergonovine* (used after labour/delivery)
  • fusidic acid, used as an antibiotic
  • lovastatin, lomitapide or simvastatin, used to reduce cholesterol levels
  • lurasidone and pimozide, for mental health conditions
  • neratinib, for breast cancer
  • ranolazine, for chronic angina (chest pain)
  • rifampin and saquinavir, used to treat tuberculosis (these drugs should not be taken with ritonavir)
  • rivaroxaban, used as an anticoagulant
  • salmeterol, used for asthma and chronic obstructive pulmonary disease
  • St. John’s wort (Hypericum perforatum), a herbal medicine used to treat depression
  • triazolam and midazolam* (oral or injection), used to relieve anxiety and/or sleep disorders
  • PDE5 inhibitors: vardenafil, used to treat erectile dysfunction, or sildenafil when used to treat pulmonary arterial hypertension
  • voriconazole, used as an antifungal agent
  • venetoclax, at initiation of treatment and during the dose-escalation period, used to treat chronic lymphocytic leukemia
  • carbamazepine, phenobarbital and phenytoin, used as anticonvulsants (epilepsy)
  • medications used to treat erectile dysfunction, like tadalafil
  • medications used to treat pulmonary arterial hypertension, like bosentan or tadalafil
  • medications used to lower blood cholesterol, such as atorvastatin and rosuvastatin
  • certain medications that affect the immune system, such as cyclosporine, sirolimus and tacrolimus
  • certain medications used to treat seasonal allergies and ear and eye infections, such as budesonide, dexamethasone, fluticasone propionate, prednisone and triamicinolone
  • medications used to treat AIDS and AIDS-related infections, such as amprenavir, indinavir*, nelfinavir, saquinavir, didanosine*, rifabutin, tipranavir, delavirdine*, atazanavir, maraviroc, fosamprenavir, raltegravir, tenofovir and darunavir
  • medications used to treat depression, such as trazodone, desipramine and bupropion
  • certain medications for heart problems, such as calcium channel blockers, including diltiazem, nifedipine and verapamil
  • medications used to regulate heart rhythms, such as systemic lidocaine and digoxin
  • antifungals such as ketoconazole and itraconazole*
  • morphine-like medications used to relieve severe pain, such as methadone and meperidine
  • anticoagulants, such as warfarin
  • some antibiotics, such as rifabutin and clarithromycin
  • antibiotics used to treat tuberculosis, such as rifampin
  • bronchodilators used to treat asthma, such as theophylline
  • anti-cancer medications such as abemaciclib, dasatinib, encorafenib, ibrutinib, nilotinib, vincristine and vinblastine
  • medications used to treat low blood platelet counts, such as fostamatinib
  • some medications for heart rhythm disorders, such as mexiletine and disopyramide
  • some anticonvulsants, such as clonazepam, divalproex, lamotrigine and ethosuximide
  • certain narcotic analgesics, such as all forms of fentanyl, tramadol and propoxyphene
  • quetiapine used to treat schizophrenia, bipolar disorder and major depressive disorder
  • medications used to treat hepatitis C, such as simeprevir, glecaprevir/pibrentasvir or ombitasvir, paritaprevir and ritonavir with or without dasabuvir*;
  • certain sedatives or medications used to treat anxiety, such as buspirone, clorazepate, diazepam, flurazepam and zolpidem
  • stimulants, such as methamphetamine
  • medications used to relieve pain associated with endometriosis, such as elagolix
  • medications used to treat depression, such as amitriptyline, clomipramine, fluoxetine, imipramine, maprotiline*, nefazodone*, nortriptyline, paroxetine, sertraline, trimipramine
  • medications used to treat nausea and vomiting, such as dronabinol*;
  • medications used to treat pneumonia, such as atovaquone
  • medications used for sedation and drugs used to help you sleep (hypnotics), such as estazolam
  • medications used to reduce intraocular pressure, such as timolol
  • medications used to reduce blood pressure, such as metoprolol
  • medications used to treat HIV, such as efavirenz;
  • medications used to prevent rejection of transplanted organs, such as everolimus and rapamycin
  • medications used to treat certain mental or mood disorders, including schizophrenia and bipolar disorder, such as perphenazine, risperidone and thioridazine
  • medications used as hormonal contraceptives containing ethinyl estradiol (“The Pill”)