Diagnosis of sulfonamide hypersensitivity reactions by in-vitro "rechallenge" with hydroxylamine metabolites.

Study Objective: To determine whether differences in in-vitro detoxification of sulfonamide-reactive metabolites can be detected among the lymphocytes from controls, patients with sulfonamide hypersensitivity reactions, and patients with nonhypersensitivity reactions to the sulfonamide agents.
Design: In-vitro toxicity assay on lymphocytes.
Setting: Clinics for adverse drug reactions in an adult and pediatric tertiary care center.
Patients: Peripheral blood lymphocytes were obtained from 46 normal volunteers and 76 patients referred to the clinic for assessment of adverse drug reactions to sulfonamide agents. Thirty-one patients had clinical histories consistent with a diagnosis of hypersensitivity reaction, whereas 45 patients had clinical histories felt to be inconsistent with a diagnosis of hypersensitivity reaction.
Interventions: Lymphocytes were assayed with tetrazolium to determine toxicity from the hydroxylamine of sulfamethoxazole.
Measurements and Main Results: The lymphocytes from patients with a history of hypersensitivity reactions showed markedly increased toxicity across a tenfold-concentration toxicity-concentration curve compared with those from controls and patients with a history of nonhypersensitivity reactions. These differences were highly significant (P less than 0.01). No difference was found between the toxicity shown by the lymphocytes from controls and that shown by the lymphocytes from patients with a history of nonhypersensitivity reactions.
Conclusions: Metabolic differences in the production and detoxification of reactive metabolites of sulfonamide agents are important determinants of hypersensitivity reactions to these agents. These results suggest that the hydroxylamine derivative of sulfamethoxazole may be a reactive metabolite mediating these reactions. Sulfonamide hydroxylamines are useful in the diagnosis and study of the pathogenesis of hypersensitivity reactions to sulfonamide agents.