Immunochemical Approaches to the Detection of Sulfathiazole in Animal Tissues

A series of ELISAs based on anti-sulfathiazole (STZ) monoclonal antibodies (MAbs) were developed that can detect STZ below the tolerance level in tissues. The IC₅₀ values (concentrations of STZ inhibiting 50% of binding in a competitive ELISA) for each MAb ranged from 6 to 21 ng ml^-1 of STZ. Immunoassays based upon two MAbs, STZ-23 and SDM44, were evaluated for their assay performance using swine liver samples spiked with STZ. Swine liver tissue was analyzed without a complex sample preparation step, with only a simple dilution of swine liver extract being necessary. A good correlation between immunoassay results and spike levels in swine liver (R² >0.98) was obtained, demonstrating that the immunoassays are capable of quantifying STZ in swine liver. The cross-reactivities of other sulfonamide drugs and STZ metabolites in these immunoassays were also examined.