Oral challenge in patients with suspected cutaneous adverse drug reactions: findings in 784 patients during a 25-year-period.

The aim of this study was to analyse the usefulness of oral challenge test with different drugs in confirming cutaneous adverse drug reactions in routine clinical practice. During the years 1975-2000 a total of 1,001 challenges were carried out in 784 patients. Patients with serious drug reactions were excluded and those with positive skin test reactions were challenged only in dubious cases. Of 1,001 challenges, 136 (13%) patients developed a positive challenge reaction. Antimicrobial drugs were most commonly suspected, accounting for 67% of challenges and 66% of the positive reactions. Exanthema was the most common skin reaction (72%), followed by fixed drug eruption (16%) and urticaria (12%). One serious challenge reaction with salazosulfapyridine was seen. We conclude that the challenge test is most useful as a tolerance test or to exclude drug hypersensitivity. It may be useful to complete studies of adverse drug reactions in patients with a history of exanthema, if other diagnostic methods are not available or if other diagnostic tests yield negative results. Out-patient protocol can be used in most cases.