10.6 Pharmacovigilance and Adverse Drug Reaction Reporting in Canada
Key Takeaways
- Health Canada's Canada Vigilance Program receives adverse reaction and medical device incident reports, and reporting by health professionals and consumers is voluntary.
- Under Vanessa's Law, Canadian hospitals must report serious adverse drug reactions and medical device incidents to Health Canada within 30 days.
- A serious adverse reaction is one that is fatal or life-threatening, requires or prolongs hospitalisation, causes persistent disability, results in a congenital malformation, or requires intervention to prevent one of these.
- The Naranjo algorithm scores causality as definite, probable, possible, or doubtful using rechallenge, dechallenge, timing, and alternative explanations.
- Type A reactions are dose-related and predictable from pharmacology, whereas type B reactions are idiosyncratic, unpredictable, and often immunologic.
10.6 Pharmacovigilance and Adverse Drug Reaction Reporting in Canada
Exam Focus: "Adverse drug reaction reporting" is an explicit syllabus bullet under medication and patient safety practices. Items test the classification of a reaction, the causality assessment, and the Canadian reporting obligation.
Why Post-Market Surveillance Exists
Pre-market clinical trials are limited by design. They enrol a few hundred to a few thousand carefully selected participants, run for months rather than years, and exclude children, pregnant people, and those with significant comorbidity or polypharmacy. Consequently they cannot detect rare reactions, delayed reactions, reactions in excluded populations, or interactions that appear only in real-world use.
The rule of three captures the limitation: to have a 95% chance of observing at least one occurrence of an event with an incidence of 1 in n, roughly 3n patients must be exposed. A reaction occurring in 1 in 10,000 patients will almost certainly not appear in a 3,000-patient trial. Post-market surveillance is therefore not a formality; it is where most serious rare reactions are discovered.
Classifying Adverse Drug Reactions
| Type | Name | Characteristics | Examples |
|---|---|---|---|
| A | Augmented | Dose-related, predictable from pharmacology, common, low mortality | Bleeding on an anticoagulant, hypoglycemia on a sulfonylurea, bradycardia on a beta-blocker |
| B | Bizarre | Not dose-related, unpredictable, uncommon, higher mortality | Anaphylaxis, Stevens-Johnson syndrome, idiosyncratic hepatotoxicity |
| C | Chronic | Related to cumulative dose and duration | Osteonecrosis of the jaw with bisphosphonates, adrenal suppression with corticosteroids |
| D | Delayed | Appears long after exposure | Carcinogenesis, tardive dyskinesia |
| E | End of use | Occurs on withdrawal | Benzodiazepine withdrawal, corticosteroid adrenal crisis, rebound acid hypersecretion |
| F | Failure | Unexpected therapeutic failure, often from interaction | Contraceptive failure with an enzyme inducer |
Type A reactions are managed by dose reduction and monitoring; type B reactions usually require permanent avoidance and documentation of a true allergy.
An adverse drug reaction is a noxious and unintended response to a drug at normal doses, whereas an adverse drug event is any harm associated with drug use including that caused by error. Distinguishing them matters: an error is addressed through the quality improvement system, while a genuine reaction is addressed through pharmacovigilance.
Assessing Causality
Before reporting, assess how likely it is that the drug caused the event. The Naranjo algorithm scores factors including previous conclusive reports, temporal relationship, response to dechallenge, response to rechallenge, alternative causes, dose-response relationship, and objective confirmation. Total scores classify the reaction as definite (9 or more), probable (5 to 8), possible (1 to 4), or doubtful (0 or less).
The practical questions behind the score:
- Timing — is the interval between starting the drug and the event biologically plausible?
- Dechallenge — did the event improve when the drug was stopped or the dose reduced?
- Rechallenge — did it recur on re-exposure? Deliberate rechallenge is usually unethical for serious reactions.
- Alternative explanations — could the underlying disease, another drug, or an unrelated illness account for it?
- Prior reports — is this reaction described in the literature or the product monograph?
Uncertain causality is not a reason to withhold a report. Signal detection works by aggregating uncertain individual reports.
The Canadian Reporting System
Canada Vigilance is Health Canada's national post-market surveillance program. It collects reports of suspected adverse reactions to pharmaceuticals, biologics, natural health products, and radiopharmaceuticals, along with medical device incidents. Reports may be submitted online, by telephone, by fax, or by mail, and are also accepted through the manufacturer.
Who reports, and whether it is mandatory:
| Reporter | Obligation |
|---|---|
| Health professionals in the community, including pharmacists | Voluntary |
| Consumers and patients | Voluntary |
| Hospitals | Mandatory for serious adverse drug reactions and medical device incidents, within 30 days of first documentation, under Vanessa's Law |
| Market authorisation holders (manufacturers) | Mandatory, with defined expedited timelines |
Vanessa's Law — the Protecting Canadians from Unsafe Drugs Act — amended the Food and Drugs Act to strengthen post-market oversight. It introduced mandatory hospital reporting of serious adverse drug reactions and medical device incidents, and it gave the Minister of Health powers to order a label change, order a recall, compel post-market studies, and disclose confidential business information where there is a serious risk to health.
A serious adverse reaction is one that is fatal or life-threatening, requires or prolongs hospitalisation, results in persistent or significant disability or incapacity, causes a congenital malformation, or requires intervention to prevent one of these outcomes. Severity and seriousness are not the same thing: a severe headache is not "serious" in the regulatory sense, while an asymptomatic arrhythmia requiring admission is.
What to report. Health Canada particularly encourages reports of serious reactions, unexpected reactions not described in the labelling, reactions to newly marketed products, and reactions to natural health products. Include the patient's age, sex, and relevant history; the suspected product with dose, route, and dates; the reaction with its onset, course, and outcome; concomitant medications; and the results of dechallenge or rechallenge.
Adverse events following immunization follow a parallel route, reported to local public health for entry into the national surveillance system.
From Signal to Action
Reports are analysed for signals — a possible causal association previously unknown or incompletely documented. A validated signal can lead to a label and monograph change, a Health Canada risk communication or health product advisory published through the recalls and safety alerts database, a required post-market study, a restriction of the indication, or, rarely, market withdrawal.
Pharmacists are positioned to see what no other clinician sees: the complete dispensing history across prescribers, the non-prescription and natural health products, and the patient's own account of what happened. Practically, this means asking directly about new symptoms after a therapy change, considering a drug cause before adding a new drug to treat a symptom — the prescribing cascade — documenting reactions in the patient record with the reaction described rather than simply labelled "allergy", and submitting the report.
Recording "penicillin allergy" without describing the reaction causes lasting harm, because it drives a lifetime of broader-spectrum, more toxic, and less effective antibiotic use. Record what happened, when, and how it was managed.
A hospital pharmacist documents a serious adverse drug reaction in an inpatient. Under Vanessa's Law, what is the reporting obligation?
A patient develops Stevens-Johnson syndrome two weeks after starting lamotrigine. How is this reaction classified?
Which finding would most increase the Naranjo causality score for a suspected adverse drug reaction?
A pharmacist notes that a patient started on metoclopramide for reflux has been prescribed benztropine for a new tremor. What phenomenon should be considered first?