Immunochemical analysis of sulfonamide drug allergy: identification of sulfamethoxazole-substituted human serum proteins.

BACKGROUND: Sulfonamides undergo oxidative metabolism to yield reactive metabolites that haptenate proteins readily. Although it has been shown that sulfonamide metabolites bind covalently to murine microsomes, sulfonamide-conjugated serum proteins have not been analyzed in the peripheral blood of treated individuals.
OBJECTIVE: We hypothesized that during treatment with sulfamethoxazole, intracellular proteins are haptenated by drug metabolites, and some of these are destined for secretion into the serum.
METHODS: Using antibodies specific for sulfamethoxazole and an alkaline phosphatase immunoblotting technique, we attempted to demonstrate the presence of sulfamethoxazole-substituted proteins in the serum of individuals during a course of treatment.
RESULTS: Five days into therapy, serum protein haptenation by sulfamethoxazole was demonstrated in two of the three individuals studied. In addition, Western blot analysis revealed that haptenation is not indiscriminate, but highly selective. A single 30 kd protein is the target of haptenation in all instances. A kinetic analysis revealed that substituted proteins can be detected early, within hours of administration. Moreover, haptenated proteins remain detectable in the serum 48 hours after discontinuation of the drug.
CONCLUSION: The results presented here constitute the first direct evidence that sulfonamides, on being metabolized, covalently haptenate human serum proteins during a course of therapy.