Adverse drug reactions

Adverse drug reactions are unwanted or undesirable reactions to drugs that occur in normal conditions. They are relatively common, occurring in 10-20% of hospital inpatients, and are usually classified as type A (augmented) or type B (bizarre) reactions. Type A reactions are usually well-known, predictable effects that are related to drug dosage. They are more common in elderly patients and in those with renal or hepatic impairment. Type B reactions are often unrelated to the main pharmacological effects of drugs, and are usually dose-independent, relatively uncommon and unpredictable. In many instances, their aetiology is - obscure, although they are sometimes related to genetic - predisposition or drug hypersensitivity. In anaesthetic practice, important reactions - related to genetic predisposition include malignant hyperthermia, suxametho-nium apnoea and hepatic porphyria. In contrast, hypersensitivity or allergic responses to drugs depend on immunological factors, and are usually divided into four main types. Type I hypersensitivity (immediatetype - hypersensitivity) is responsible for many of the type B reactions - associated with drugs, and may cause hypotension, bronchospasm, - facial and labial oedema, laryngeal oedema and urticaria.