Cross-reactivity between quinolones is uncertain. Recently, we studied three patients who had developed suspected allergic reactions to a quinolone. For all of them we performed skin test, histamine release test, RAST, and oral provocation with the suspected quinolone and also with another quinolone of the opposite generation. Five atopic and five nonatopic subjects were used as controls. Neither skin test, histamine release test, nor RAST was useful in the diagnosis. By means of oral controlled provocation, the reactions were reproduced, and all the patients also reacted to another quinolone. We concluded that cross-reactivity between quinolones seems to be very important, and avoidance of any quinolone should be recommended to any patient who has suffered an allergic reaction to one of these drugs.

We present two patients who experienced life-threatening immediate reactions and one patient who developed generalized urticaria following oral administration of trimethoprim (TMP) and sulfamethoxazole (SMX) combination. Skin prick tests with TMP were positive in the three patients. No patients reacted to skin prick tests with SMX. No significant levels of IgE antibodies to TMP were found by RAST in the serum of the patients. Normal subjects used as controls did not react to any of these tests. Single-blind, placebo-controlled oral challenges were positive with TMP and negative with SMX in all patients. These results suggest that the three patients developed type I hypersensitivity reactions to TMP. In our patients skin prick tests with TMP were useful in TMP hypersensitivity diagnosis.