Pharmacodynamics: Adverse Drug Reactions (ADRs)
Learning Objectives
- Define adverse drug
reactions (ADRs).
- Classify types of ADRs.
- Identify predisposing
factors for ADRs.
- Understand hypersensitivity
and its types.
Definition of Adverse Drug Reactions (ADRs)
- Definition:
- Any unintended and harmful
reaction to a drug at normal therapeutic doses.
- Key Points:
- Distinct from side effects
(predictable and often mild).
- Can occur immediately or
after prolonged use.
Types of ADRs
- Classification:
- Type A (Augmented):
- Predictable
and dose-dependent.
- Examples:
Hypoglycemia from insulin, bleeding from anticoagulants.
- Type B (Bizarre):
- Unpredictable
and dose-independent.
- Examples:
Anaphylaxis from penicillin.
- Type C (Chronic):
- Occurs
with long-term use.
- Examples:
Osteoporosis from corticosteroids.
- Type D (Delayed):
- Manifests
after a delay.
- Examples:
Carcinogenesis from chemotherapeutic agents.
- Type E (End of Use):
- Due
to drug withdrawal.
- Examples:
Withdrawal seizures from benzodiazepines.
- Type F (Failure):
- Failure
of therapy.
- Examples:
Antibiotic resistance.
Predisposing Factors for ADRs
- Patient-Related Factors:
- Age (e.g., elderly or
pediatric patients).
- Gender (e.g., women more
prone to certain ADRs).
- Genetics (e.g., G6PD
deficiency).
- Comorbidities (e.g., renal
or hepatic impairment).
- Drug-Related Factors:
- Polypharmacy (use of
multiple drugs).
- High doses or prolonged
use.
- Route of administration
(e.g., IV vs. oral).
Hypersensitivity Reactions
- Definition: Exaggerated immune response
to a drug.
- Characteristics:
- Unpredictable.
- Dose-independent.
- Often involves prior
sensitization.
Types of Hypersensitivity Reactions
- Type I (Immediate):
- Mediated by IgE antibodies.
- Symptoms: Urticaria,
anaphylaxis.
- Example: Penicillin
allergy.
- Type II (Cytotoxic):
- Mediated by IgG or IgM.
- Symptoms: Hemolytic anemia,
thrombocytopenia.
- Example: Methyldopa-induced
hemolysis.
- Type III (Immune Complex):
- Immune complexes deposit in
tissues.
- 8Symptoms: Serum sickness,
vasculitis.
- Example: Sulfonamide reactions.
- Type IV (Delayed):
- T-cell mediated.
- Symptoms: Contact
dermatitis, organ rejection.
- Example: Tuberculin skin
test reaction.
Clinical Implications of ADRs
- Impacts:
- Increased morbidity and
mortality.
- Higher healthcare costs.
- Need for additional
treatments or interventions.
- Prevention Strategies:
- Careful patient history and
screening.
- Monitoring for early signs
of ADRs.
- Avoidance of known
allergens or cross-reactive drugs.
Summary
- ADRs are unintended and
harmful drug reactions.
- Types of ADRs include Type A
(predictable) and Type B (unpredictable).
- Predisposing factors include
patient- and drug-related variables.
- Hypersensitivity is an
immune-mediated ADR with four major types.
References
- Goodman & Gilman’s The
Pharmacological Basis of Therapeutics.
- Rang & Dale’s
Pharmacology.
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Chapter -1 Chapters in Pharmacology
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