Sulfonamides are widely used for therapeutic and prophylactic purposes in animal food production. Sulfonamides which are retained in food could result in allergic or toxic reactions in sulfonamide sensitive consumers. Also, there are general concerns that the widespread use of antibiotics could contribute to antibiotic resistance in pathogenic organisms. Maximum Residue Limits (MRLs) for sulfonamides in tissues have been established in many countries. In the European Union, the United States and Canada a MRL of 100 µg/kg is set. In Japan, a zero residual level is applied. Therefore sensitive methods for monitoring these residues are required to ensure that the animal tissues are safe for human consumption.

Euro-Diagnostica has developed three specific EIA kits for three different sulfonamides: the Sulfamethazine EIA, the Sulfadiazine EIA and the Sulfaquinoxaline EIA. Furthermore, a multiscreening ELISA kit for screening for six different sulfonamides in one EIA test is available.

The Sulfamethazine (Sulfadimidine) EIA is a competitive enzyme immunoassay for the screening of urine, tissue, plasma and milk samples on the presence of this antimicrobial agent. The dose-response curve shows a measuring range for sulfamethazine of 0.2 – 10 ng/ml. The antibody reacts with sulfamerazine (15% cross-reactivity) and shows high cross-reactivity (130%) towards the major metabolite N4-acetyl-sulfamethazine. The cross-reactivities of ten other sulfonamides (sulfadiazine, sulfadimethoxine, sulfadoxine, sulfaguanidine, sulfamethoxazole, sulfamethoxydiazine, sulfapyridine, sulfaquinoxaline, sulfathiazole and sulfatroxazole) are < 0.5%. Urine and plasma samples can be used to predict the level of sulfamethazine in tissues. In pig urine, acetylation is the major elimination pathway of sulfamethazine and about 75% is excreted as N4-acetyl-sulfamethazine. Due to the presence of the metabolite in urine and the sensitivity of the Sulfamethazine EIA, low concentrations in tissue can be screened for. Diluted urine, plasma and defatted milk samples can be analysed directly. For tissues, an extraction procedure is available.

The Sulfadiazine EIA is a competitive enzyme immunoassay for the screening of urine, tissue, plasma and milk on the presence of this antimicrobial agent. The dose-response curve of the sulfadiazine shows a measuring range of 0.1 - 10 ng/ml. The antibodies show high cross-reactivities towards sulfamerazine (75%) and the major metabolite N4-acetyl-sulfadiazine (50%). Other sulfonamides show low cross-reactivities: sulfathiazole (3%), sulfa-methazine (0.5%), sulfapyrine (0.5%), sulfamethoxy-diazine (0.5%), sulfamethoxine (< 0.1%), sulfadoxine (< 0.1%), sulfaguanidine (< 0.1%), sulfamethoxazole (< 0.1%), sulfaquinoxaline (< 0.1%). Sample treatment is similar to the Sulfamethazine-EIA.

The Sulfaquinoxaline EIA is a competitive enzyme immuno assay for the screening of urine, tissue, milk and plasma samples on the presence of this antimicrobial agent. The dose-response curve of the sulfaquinoxaline shows a measuring range of 5-500 ng/ml. The antiserum used in this EIA is specific for sulfaquinoxaline and does not show any cross-reactivity (< 0.1%) with all other sulfonamides tested.