Adverse cutaneous reactions to drugs.

Drug eruptions are probably the most frequent of all manifestations of drug sensitivity. They occur in about 2% of treatment courses and are commoner in women, the elderly and in patients with the acquired immunodeficiency syndrome (AIDS), especially from sulphonamides such as in co-trimoxazole1. Drugs most often incriminated are listed in Table 1. The prevalence of a history of penicillin allergy has been estimated as up to 10%, and reactions to sulphonamides may affect 5% of those treated. Potentially fatal conditions such as Stevens–Johnson syndrome and toxic epidermal necrolysis are fortunately rare (0.5–1.8 cases per million per year)2. Adverse drug reactions may reflect immunological drug allergy or, more usually, non-immunological mechanisms. Idiosyncratic reactions are independent of dose, unrelated to the pharmacological action of the drug and may have a genetic basis3. This article lists the commonest clinical patterns of drug eruptions (excluding contact dermatitis) and reviews their management.