The level and nature of the albendazole residues in milk of treated cows were determined as a function of the time of milking (12-h intervals), and the fate of those residues during cheesemaking, ripening, and storage was examined when the obtained milk was used for making Teleme cheese. Ion-pair liquid chromatographic analysis with fluorescence detection showed that the albendazole sulfoxide metabolite reached its maximum (523 ± 199 μg/kg) at the lst milking and declined below the detection limit by the 4th milking. The sulfone metabolite attained its highest level (812 ± 99 μg/kg) more slowly (at the 2nd milking) and declined below detection limit by the 13th milking. The 2-aminosulfone metabolite, which was present in the milk obtained at the lst milking, reached its maximum (128 ± 36 μg/kg) at the 3rd milking, and slowly declined to a level below detection limit by the 15th milking. Whey and cheese analysis revealed that about 70% of each major metabolite initially present in milk could be distributed in the whey. The remaining 30% occurred in the cheese at residue levels higher than those initially present in the milk of the 1st or 2nd milking (688 versus 445 or 450 versus 230 μg/kg for albendazole sulfoxide; 890 versus 608 or 1502 versus 783 μg/kg for albendazole sulfone; 19 versus 15 or 161 versus 105 μg/kg for albendazole 2-aminosulfone). Ripening and storage of the cheeses made from milks from the lst or 2nd milkings results in a decrease of the sulfoxide metabolite (to 225 or 206 μg/kg), an increase of the sulfone metabolite (to 1,181 or 1,893 μg/kg), and no effect on the 2-aminosulfone metabolite.
Ion-pair high-performance liquid chromatographic analysis of sulpyrine and its metabolites in rabbit plasma.
