Topical provocation of fixed drug eruption.

To determine whether topical provocation could be used for the diagnosis of fixed drug eruption (FDE) instead of systemic provocation, we applied the suspected drug at various concentrations (1-10%) in either petrolatum, 94% ethanol or dimethyl sulphoxide (DMSO) as an open test on both clinically normal skin and on previous FDE lesions in 24 patients with established FDE due to phenazone salicylate, a sulphonamide, doxycycline, trimethoprim, chlormezanone, a barbiturate, or carbamazepine. In 18 of the 24 patients, local provocation of FDE was seen at sites or previous eruption but never on clinically normal skin. With some drugs, e.g. phenazone salicylate, positive provocation of FDE was seen with all the vehicles used; with sulphamethoxazole and trimethoprim, a positive result was seen only in DMSO. To study cross-reactions to other phenazone derivatives in patients with an FDE caused by phenazone salicylate, we applied topical phenazone, aminophenazone and propyphenazone to sites of previous FDE lesions in three patients. In all three, a positive reaction was seen with phenazone, but only one patient showed positive results with aminophenazone and propyphenazone. The present study suggests that topical provocation is useful with several drugs causing FDE. Testing should always be performed on sites of previous FDE, and the sensitivity of the open topical testing can be increased in certain cases by using a vehicle which increases penetration of the drug.