Single-dose oral tolerance test with alternative compounds for the management of adverse reactions to drugs

BACKGROUND: Adverse reactions to drugs are common in the clinical practice. Many outpatients are frequently referred to allergists in order to determine which drugs they can safely take in the future. OBJECTIVE: We set up an oral single-dose tolerance test procedure to find out for each patient one or more alternative drugs that can be taken when needed. METHODS: 452 outpatients (130 male, 322 female) with well-documented reactions (urticaria/angioedema, respiratory symptoms, laryngeal edema, anaphylaxis, exfoliative skin diseases) underwent the challenge. All tests were preceded by a single-blind placebo: if a reaction occurred, a second placebo was administered. Otherwise, a single dose (1/10 of the therapeutic one) of an alternative drug was given blindly and the patient was then observed for 6 h. The drugs used were different in structure from those suspected of having caused the adverse reaction. The patients were followed up at 4- to 6-month intervals, in order to detect any reaction that may have occurred with the tested drugs. RESULTS: 98 patients (89 women) had untoward reactions after the first placebo and 34 out of them reacted to the second placebo, too. During challenges the reaction rate ranged between 4.6 and 9.0%; these reactions were easily managed and none of them was severe. We followed up 407 patients: 87.2% of them were able to use one or more of the suggested drugs without reactions, 9.3% did not take the drugs and only 3.5% reported reactions to the previously tested drugs. CONCLUSION: The challenge procedure proved to be a simple tool for managing patients with adverse reactions to drugs. Its safety and reliability were validated by a long-term follow-up.