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.