Albendazole residues in goat's milk: Interferences in microbial inhibitor tests used to detect antibiotics in milk.

Albendazole (ABZ) residues in goat's milk and their effect on the response of microbial inhibitor tests used for screening antibiotics were evaluated. A total of 18 Murciano-Granadina goats were treated with ABZ and individually milked once a day over a 7-day period. ABZ quantification was performed by high performance liquid chromatography. The ABZ parent drug was not detected. The maximum concentration of its metabolites (ABZ sulfoxide, ABZ sulfone, and ABZ 2-aminosulfone) was reached on the 1st day post treatment (260.0 ± 70.1 µg/kg, 112.8 ± 28.7 µg/kg, 152.0 ± 23.6 µg/kg, respectively), decreasing to lower than the maximum residue limit (MRL, 100 µg/kg) on the 3rd day post treatment. Milk samples were also analyzed by microbial tests [Brilliant Black Reduction Test (BRT) MRL, Delvotest SP-NT MCS and Eclipse 100], and only one positive result was found for Delvotest SP-NT MCS and Eclipse 100. However, a high occurrence of positive outcomes was obtained for BRT MRL during 6 days post treatment, whereas ABZ residues were not detected from the 4th day post administration, suggesting that factors other than the antiparasitic agent might affect the microbial test response.