Comparison of milk residue profiles after oral and subcutaneous administration of benzimidazole anthelmintics to dairy cows

The current experimental work reports on the comparison of the milk residue profile of the benzimidazole (BZD) anthelmintics after their administration by the oral and subcutaneous (SC) routes to dairy cows. The cows were distributed in four groups and treated as follows-Group 1: oxfendazole (OFZ) by oral route (5 mg kg−1); Group 2: albendazole (ABZ) by oral route (5 mg kg−1); Group 3: albendazole sulphoxide (ABZSO) by SC administration (3 mg kg−1); Group 4: OFZ by SC route (3 mg kg−1). After drug administrations milk samples were collected and frozen at −20 °C until analyzed by liquid chromatography (LC). A complete validation of the analytical methodology was accomplished. Regression curves were linear over the concentrations examined and the correlation coefficients (r) ranged between 0.994 and 0.999. The mean extraction recovery range between 77 and 97%. Residual concentrations of OFZ, fenbendazole sulphone (FBZSO2) and FBZ were recovered in milk after OFZ oral administration. OFZ reached the highest concentration in milk (0.39 ± 0.10 μg ml−1) at 12 h post-treatment, being detected up to 72 h post-treatment. In contrast, FBZ was not detected in cow milk and FBZSO2 was the main analyte recovered from the milk with the maximum milk residues (0.042 ± 0.003 μg ml−1) achieved at after 36 h following the SC injection of OFZ. ABZSO and ABZSO2 were the metabolites recovered in milk following oral (ABZ) and SC (ABZSO) treatments in dairy cows. ABZSO2 was the analyte recovered at the highest residual concentration (0.86 ± 0.33 μg ml−1) at 12 h after oral administration of ABZ. However, ABZSO was the main compound measured in cow milk following its SC injection (0.18 μg ml−1) at 12 h post-treatment. Overall, the total milk residue levels (sum of parent drug and metabolites) were higher after oral compared to parenteral treatments in dairy cows. These results reported here are discussed according to the acceptable maximum residue limits (MRLs) established for BZD compounds in cow milk.