Adverse Reactions

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Adverse Reactions

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

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