Epidemiology

In one US study of 15,438 consecutive medical inpatients, 347 patients had 358 skin reactions, an overall reaction rate of 2.2%.[24] Each had taken a mean of 8 different drugs. Rashes were attributed to 51 drugs, and 75% of the allergic skin reactions were attributed to antibiotics, blood products, and inhaled mucolytics. Amoxicillin (51 reactions per 1000 patients exposed), trimethoprim/sulfamethoxazole (34 reactions per 1000 patients exposed), ampicillin (33 reactions per 1000 patients exposed), and cephalosporins (13 reactions per 1000 patients exposed) had the highest rates. In a Finnish study, about 30% of reported adverse reactions to systemic drugs involved the skin.[25] Of these, about 46% were maculopapular rashes, 23% urticaria, 10% fixed eruptions, and 5% erythema multiforme. In Mexico, 35 (prevalence of 0.7%) adverse cutaneous drug reactions (ACDR) were seen among 4785 discharged patients.[26] Drugs that were most frequently associated with ACDR were amoxicillin/clavulanate, amphotericin B, and metamizole. The most commonly seen dermatoses were morbilliform rash (51.2%), urticaria (12.2%), and erythema multiforme (4.9%). Six of the 35 cases identified were in patients who had been admitted to hospital due to a severe drug reaction (1.3/1000 patients). One died from complications directly related to the ACDR, representing a 16.6% mortality among those admitted for an ACDR and 0.02% among the global mortality.

In children, cutaneous drug reactions are the most prevalent ADRs in those hospitalized, with an estimated rate of 2% to 3%. In a study of 326 children with cutaneous ADR, L-asparaginase (16%), amoxicillin (8.3%), trimethoprim/sulfamethoxazole (7.2%), carbamazepine (4.9%), and lamotrigine (3.7%) accounted for 40% of all suspected medications.[27]

The rates of reactions to specific drugs are difficult to assess because many are reported only anecdotally.[28] Allergic reactions to beta-lactam antibiotics occur in about 3% of exposed people. Of those who develop a class I allergic reaction to a penicillin, a high proportion cross-react to a cephalosporin; those who have class III reactions have a low risk of cross-reaction.

The risks of contact dermatitis with topical medications are not well described, because most cases are reported anecdotally. The risk of contact dermatitis with topical corticosteroids may be as high as 6%.[29]

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