Residues of Anthelminthic Drugs

To determine the stability of albendazole residues in milk upon storage at 18 C from 3 to 8 months, both incurred and spiked milk samples containing all three albendazole metabolites, namely albendazole sulfoxide, albendazole sulfone, and albendazole 2-aminosulphone, were used. Results showed that the 3 month storage did not produce any change in the concentration of the analytes 

Since not all milk enters the human food chain directly, but most of the milk produced is normally subjected to some kind of processing for preparation of various dairy products, the fate of incurred albendazole residues during cheesemaking, ripening, and storage has been also investigated (87). Albendazole residues in dairy products would be of major concern if the transfer and accumulation were significant. 

Results showed that about 70% from each major albendazole metabolite initially present in milk could be distributed in the whey. The remaining 30% appeared in the produced cheese at residue levels higher than those initially present in milk (688 ppb versus 445 ppb, or 450 ppb versus 230 ppb for albendazole sulfoxide 890 ppb versus 608 ppb, or 1502 ppb versus 783 ppb for albendazole sulfone 19 ppb versus 15 ppb, or 161 ppb versus 105 ppb for albendazole-2-aminosulfone). Ripening and storage of the prepared cheeses resulted in decrease of the sulfoxide metabolite to 225 ppb or 206 ppb, increase of the sulfone metabolite to 1181 ppb or 1893 ppb, whereas it had no effect on the 2-aminosulfone metabolite. 

The thermal stability of oxfendazole has been examined in both water and cooking oil (88). Some evidence of instability was observed in boiling water after 3 h. This instability was associated with hydrolysis of the carbamate group of the oxfendazole molecule and formation of an amine byproduct. In hot cooking oil at 150 C or 180 C, the half-life of oxfendazole was 15 min or 6 min, respectively. The instability was also associated with the formation of the amine byproduct, which increased as the concentration of the parent drug decreased. 

The effect of cooking on incurred residues of oxfendazole in cattle liver has been also investigated (88). However, the results drawn from this study are inconclusive due to several variable factors. One such factor is the unstable equilibrium between oxfendazole, oxfendazole sulfone, and fenbendazole in the incurred tissue. Other factor is the overall instability of oxfendazole and its metabolites in tissue during frozen storage. Another factor is the variable distribution of the residues within the tissue used for the study and the effect of protein binding on the extractability of the residues from the tissue. It was nevertheless 

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