[Hypersensitivity to allopurinol. Efficacy of a desensitizing protocol in 3 cases]

Allopurinol is often prescribed for the treatment of hyperuricemia. It inhibits the uric acid production binding tightly to xanthine oxidase. Although it is generally well tolerated, an almost 10% prevalence of adverse reactions has been reported, particularly gastrointestinal and neurological effects. Some hypersensitivity syndromes have also been described (rash, vasculitis or exfoliative dermatitis). In these cases, if a substitute treatment is not available, a desensitization procedure to the drug must be considered. We present three patients with cutaneous hypersensitivity to allopurinol, two who developed urticaria and other one who had a fixed drug eruption. Skin test were all negatives with positive oral challenge test. An out- patient desensitization procedure to allopurinol was initiated, repeating the last tolerated doses for 4 or 5 days, and reaching maintenance therapeutic drug doses without any significant adverse effect (only one case of cutaneous pruritus). These experiences and the previously reported in the literature, show that the desensitization to allopurinol is a good therapeutic alternative in hypersensitivity reactions to the drug.