Adverse drug reaction WHO defination
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WHO definition adverse drug reaction 1972 pharmacovigilance
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Here is a complete, exam-ready breakdown of the WHO definition of Adverse Drug Reaction (ADR):
Adverse Drug Reaction (ADR) - WHO Definition
Official WHO Definition (Technical Report 498, 1972)
"A response to a drug which is noxious and unintended, and which occurs at doses normally used in man for the prophylaxis, diagnosis, or therapy of disease, or for the modification of physiological function."
- Source: WHO Technical Report Series No. 498, 1972
- Also adopted by the International Conference on Harmonization (ICH), of which WHO and the US FDA are members
Key Elements of the Definition
| Element | Meaning |
|---|---|
| "Response to a drug" | Implies a causal relationship - the drug caused the reaction, not just a coincidental occurrence |
| "Noxious" | Harmful, injurious, or undesirable |
| "Unintended" | Not a planned or expected therapeutic effect |
| "Normal doses" | Excludes intentional/accidental overdose |
| Purposes covered | Prophylaxis, diagnosis, therapy, OR modification of physiological function |
What the WHO ADR Definition EXCLUDES
- Therapeutic failure (drug not working)
- Intentional or accidental overdose
- Drug abuse
- Drug withdrawal reactions (debated)
- Medication errors (in some classifications)
ADR vs. Adverse Drug Event (ADE) - Important Distinction
| Term | WHO Definition | Causal Link? |
|---|---|---|
| ADR | Noxious, unintended response at normal doses | YES - causal relationship required |
| ADE (Adverse Drug Event) | "Any untoward medical occurrence that may present during treatment with a pharmaceutical product, but which does not necessarily have a causal relationship with this treatment" (WHO, 2005) | NOT necessarily - just temporal association |
- Every ADR is an ADE, but not every ADE is an ADR.
Updated Definition (Edwards & Aronson, 2000)
A more modern alternative definition describes an ADR as:
"An appreciably harmful or unpleasant reaction, resulting from an intervention related to the use of a medicinal product, which predicts hazard from future administration and warrants prevention or specific treatment, or alteration of the dosage regimen, or withdrawal of the product."
This is broader and more clinically relevant, as it also implies action (dose change, withdrawal, treatment).
Classification of ADRs (Rawlins & Thompson, 1977 - Augmented)
| Type | Features | Examples |
|---|---|---|
| Type A (Augmented) | Dose-dependent, predictable, common | Bleeding with warfarin, hypoglycaemia with insulin |
| Type B (Bizarre) | Dose-independent, unpredictable, rare, immunological/idiosyncratic | Anaphylaxis to penicillin, agranulocytosis with clozapine |
| Type C (Chronic) | Long-term use | Adrenal suppression with steroids |
| Type D (Delayed) | Appear after a delay | Teratogenicity, carcinogenesis |
| Type E (End of use) | Withdrawal reactions | Opioid withdrawal |
| Type F (Failure) | Failure of therapy (not classical ADR) | Oral contraceptive failure with enzyme inducers |
Pharmacovigilance Context
The WHO definition is the cornerstone of pharmacovigilance - the science of detecting, assessing, understanding, and preventing adverse effects of medicines. Reporting systems like the WHO's VigiBase and the FDA's MedWatch are built around this definition to collect global ADR data post-marketing, when rare reactions (not seen in clinical trials of a few thousand patients) become apparent in millions of users.
Pharmacovigilen e WHO defination
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WHO definition pharmacovigilance science activities detection assessment prevention adverse effects
Here is a complete, exam-ready breakdown of the WHO definition of Pharmacovigilance:
Pharmacovigilance - WHO Definition
Official WHO Definition
"The science and activities relating to the detection, assessment, understanding and prevention of adverse effects or any other medicine/vaccine related problem."
- Source: WHO - Regulation and Safety: Pharmacovigilance (originally published in The Importance of Pharmacovigilance, WHO 2002)
Breaking Down the Four Core Activities
| Activity | What it Means |
|---|---|
| Detection | Identifying new or unknown adverse effects through reporting systems (spontaneous reports, clinical trials, literature) |
| Assessment | Evaluating the causal relationship, severity, and frequency of the adverse effect |
| Understanding | Determining the mechanism, risk factors, and population at risk |
| Prevention | Taking regulatory or clinical action - warnings, dose changes, contraindications, or withdrawal |
Etymology of the Word
| Component | Meaning |
|---|---|
| Pharmaco- | Relating to drugs/medicines (Greek: pharmakon) |
| Vigilance | Watchfulness, alertness (Latin: vigilantia) |
The word literally means "watchfulness over drugs."
Objectives of Pharmacovigilance (WHO)
- Improve patient care and safety in relation to medicine use
- Improve public health and safety in relation to medicine use
- Contribute to the assessment of benefit, harm, effectiveness, and risk of medicines
- Encourage safe, rational, and more effective use of medicines
- Promote understanding, education, and clinical training in pharmacovigilance
- Facilitate communication to the public about medicine safety
Scope of Pharmacovigilance
Pharmacovigilance covers:
- Licensed medicines (post-marketing surveillance)
- Herbal medicines and traditional medicines
- Vaccines (Adverse Events Following Immunization - AEFI)
- Blood products and biologicals
- Medical devices (in some frameworks)
- Medicines used in clinical trials
Key Global Infrastructure
| Organization | Role |
|---|---|
| WHO Programme for International Drug Monitoring | Global coordination of PV since 1968 |
| Uppsala Monitoring Centre (UMC), Sweden | Manages VigiBase - WHO's global ADR database (18+ million reports) |
| ICH (International Council for Harmonisation) | Sets technical standards for PV across USA, EU, Japan |
| National PV Centres | Country-level reporting (e.g., CDSCO/PvPI in India, MHRA in UK, FDA MedWatch in USA) |
Historical Background - The Thalidomide Tragedy (1961)
The modern pharmacovigilance system was born from the thalidomide disaster:
- Thalidomide was prescribed to pregnant women for morning sickness
- Led to over 10,000 babies born with phocomelia (limb defects) worldwide
- This catalyzed the formation of the WHO International Drug Monitoring Programme (1968)
- Made spontaneous ADR reporting systematic, organized, and regulated globally
Pharmacovigilance vs. Related Terms
| Term | Definition |
|---|---|
| Pharmacovigilance | Science of detecting, assessing, understanding, and preventing drug-related problems |
| Drug Safety | Broader term encompassing all safety aspects of a medicine |
| Post-Marketing Surveillance (PMS) | Monitoring of drug safety after marketing approval |
| Signal Detection | Identification of new, possibly causal drug-adverse event associations |
| Risk Management | Set of PV activities to minimise risks of medicines |
Why Pharmacovigilance is Needed
Clinical trials before drug approval are limited:
- Involve only a few thousand carefully selected patients
- Short duration - rare or delayed ADRs are missed
- Exclude special populations (elderly, pregnant, children, those with comorbidities)
- Post-marketing phase exposes millions of patients, revealing ADRs not seen in trials
This is why ongoing pharmacovigilance throughout a drug's lifecycle is essential.
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