Topical provocation of fixed drug eruption. A study of 30 patients.

Topical provocation with the causative agent was performed in 30 patients with fixed drug eruption (FDE). The epicutaneous open test method was used on inactive sites of old FDE lesions. Drugs at 10% in the vehicles petrolatum, alcohol and dimethylsulfoxide (DMSO) were used as test preparations. Positive reactions were always seen with phenazone salicylate (16 patients) and carbamazepine patients (3 patients), and in an individual case from chlormezanone. Both positive and negative reactions were seen with trimethoprim (3 and 2, respectively), doxycycline (2 and 1) and sulfadiazine (1 and 1). Control tests on unaffected skin with drug preparations and pure vehicles remained negative. The present results confirm our previous observation that topical provocation is a reliable test method in FDE caused by phenazone salicylate. The present study also shows that topical provocation may be useful in FDE caused by carbamazepine. In FDE caused by trimethoprim, doxycycline and sulfonamides, a positive, but not a negative, skin reaction is informative.