Unwanted or potentially harmful effects of drugs – it is the unintended or unwanted noxious effect of drugs at a therapeutic dose (does not include overdoses). They vary from a mild response (that disappears on discontinuing drug) to a debilitating chronic illness significant cause of morbidity and mortality. Some adverse reactions may be inseparable from the drugs intended affect. Some adverse reactions are related to the sensitivity of the patient to a particular drug, so will be unpredictable.
Adverse drug reactions are believed to be responsible for up to 5% of all hospital admissions and a common cause of death. Adverse drug reactions are generally required to be reported to regulatory authorities.
Side effect minor effect, usually common – (eg drowsiness from antihistamines; GI irritation from aspirin)
Adverse reaction harmful or serious effect
Classification/types of adverse reactions:
• Type A (Augmented) (intrinsic) – tend to occur in everyone if enough of drug is given (eg postural hypotension from beta-blockers, bleeding from anticoagulants) – considered to be part of the pharmacological effect of the drug, so are predictable. These are dose related reactions. Up to 90% of adverse drug reactions.
• Type B (Bizarre) – only occur in some people – not considered part of the normal pharmacology – 3 subtypes:
• Type C (Continuous) – reaction due to long term use
• Type D (Delayed) – delayed reaction (eg carcinogenesis)
• Type E (Ending of use) – eg rebound adrenocorticol insufficiency
Adverse reactions may also be:
• Sensitivity related – the patient is hypersensitive or allergic to the drug or part of it; results from a previous sensitisation to the chemical or a structurally similar one. It may be due to the drug itself or from one of its metabolites.
• Toxicity – when drug levels exceed the therapeutic dose
• Idiosyncratic – unexpected or ‘peculiar’ response