Patient-reported multiple drug reactions: clinical profile and results of challenge testing.

BACKGROUND Some patients report hypersensitivity reactions to many drugs making it difficult to prescribe medications when they fall ill. AIM To describe the clinical profile of multiple drug hypersensitivity and the results of challenge testing in a large teaching hospital. METHODS We performed a five-year retrospective review of the records of patients who complained of reactions to two or more unrelated drugs and avoided medication because of a fear of developing reactions. Oral challenge testing was carried out in hospital with drugs suspected by the patient to cause reactions and/or commonly prescribed medications. A positive reaction was diagnosed when symptoms and signs resembled previously experienced episodes and there was no such reaction with placebo. RESULTS Twenty three patients (aged 14-65 years; 19 females) underwent challenge testing. Their complaints had been present for 1-30 years, with 2-40 drug reaction episodes reported. Antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) were most commonly implicated, and urticaria/angioedema were the most often reported manifestations. The patients underwent 3-27 challenges with 1-24 drugs. Three had positive challenge reactions with various NSAIDs, 13 developed symptoms and signs that were judged not to be true reactions, and 7 had no reactions. None of our patients qualified for a diagnosis of true multiple drug hypersensitivity. CONCLUSION Patients who believe they are allergic to multiple, pharmacologically unrelated drugs are usually mistaken. Challenge testing is a reliable way of demonstrating this and providing patients with a list of safe drugs.