Last updated:
March 9, 2026
Definition of terms
| Term | Definition |
|---|---|
| Adverse drug reaction (ADR) | A noxious and unintended response to medicine that occurs at normal therapeutic doses used in humans for prevention, diagnosis, or therapy of disease, or for the modification of physiologic function |
| Side effect | Any unintended effect of a pharmaceutical product occurring at normal therapeutic doses and is related to its pharmacological properties. Such effects may be well-known and even expected and require little or no change in patient management. |
| Serious adverse effect | Any untoward medical occurrence that occurs at any dose and results in death, requires hospital admission or prolonged hospital stay, results in persistent or significant disability, or is life-threatening |
- Patient risk factors for adverse drug reactions
- Polypharmacy
- Elderly
- Children
- Patients with multiple diseases
- Pregnancy
- Malnourished
- Immunosuppression
- Drug abusers and addicts
- Causes of adverse drug reactions
- Incorrect medicine ordering by a prescriber
- Administration of a medicine or dose that differs from the written order
- Medical negligence
- Classification of ADR by severity
- Minor: No therapy, antidote, or prolongation of hospitalisation is required.
- Moderate: Requires a change in drug therapy, specific treatment, or prolonged hospital stay.
- Severe: Potentially life-threatening, causes permanent damage, or requires intensive medical treatment.
- Lethal: Directly or indirectly contributes to the death of the patient.
- Classification of ADR by etiology
- Type A – Exaggerated pharmacological response
- Pharmacodynamic (e.g., bronchospasm from beta-blockers)
- Toxic (e.g., deafness from aminoglycoside overdose),
- Often predictable and dose-dependent e.g., propranolol and heart block, anticholinergics and dry mouth
- Responsible for at least two-thirds of ADRs
- Type B – Nonpharmacological, often an allergic response
- Rare and unpredictable
- Medicine-induced diseases (e.g., antibiotic-associated colitis)
- Allergic reactions (e.g., penicillin anaphylaxis)
- Idiosyncratic reactions (e.g., aplastic anaemia with chloramphenicol)
- Type C – Continuous or long-term (time-related): e.g., Osteoporosis with oral steroids
- Type D – Delayed (lag time): e.g., Teratogenic effects with anticonvulsants or lisinopril
- Type E – Ending of use (withdrawal): e.g., Withdrawal syndrome with benzodiazepines
- Type F – Failure of efficacy (no response): e.g., Resistance to antimicrobials
- Type A – Exaggerated pharmacological response
- Types of allergic drug reactions
- Type I – immediate, anaphylactic (IgE): e.g., anaphylaxis with penicillins
- Type II – cytotoxic antibody (IgG, IgM): e.g., methyldopa and hemolytic anaemia
- Type III – serum sickness (IgG, IgM), antigen-antibody complex: e.g., procainamide-induced lupus
- Type IV – delayed hypersensitivity (T cell): e.g., contact dermatitis to rubber
- Prevention of ADR
- Avoid inappropriate use of drugs
- Appropriate drug administration (Rational Therapeutics): Take note of the dose, dosage form, duration, route, frequency, and technique
- Ask for the previous history of drug reactions and allergies
- Always suspect ADR when a new symptom arises after initiation of treatment ( No new drug for new symptoms).
- Ask for laboratory findings like serum creatinine