Usefulness of Enzyme Immunoassay (EIA) as an Analytical Method of Sulfamethoxazole Residues in Animal Tissues

Applicability of enzyme immunoassay (EIA) for determination of drug residues in animal tissues was examined by using sulfamethoxazole (SMX) as a test drug. EIA of SMX was specific for SMX, though N4-acetyl SMX showed a higher reactivity in the system. Control swine serum and plasma spiked with 8ng/ml SMX were negative. Control liver or other tissues showed reactivity consistent with that expected when spiked with up to 25ng/g (ml) SMX. It seems necessary for the accurate determination of SMX in tissues to use standard curves prepared by adding SMX to control tissues, and in some cases by use of HPLC as well. EIA was, however, applicable as a screening method to detect SMX in chicken muscle without using control muscle when an adequate cut-off value was used.