DISTRIBUTION OF THE ANTHELMINTIC DRUG ALBENDAZOLE AND ITS MAJOR METABOLITES IN-OVINE MILK AND MILK-PRODUCTS AFTER A SINGLE ORAL DOSE

The distribution of albendazole (ABZ) and its main metabolites albenda zole sulphoxide (ABZSO), albendazole sulphone (ABZSO(2)) and albendazo le 2-aminosulphone (NH(2)ABZSO(2)) were investigated in bulk milk and milk products after administration of a single oral dose of the drug ( 12.5 mg/kg) to 80 Laticauda sheep. An analytical method was developed for this investigation from an existing procedure used for the determi nation of these compounds in plasma and digesta samples. No traces of the parent compound or NH(2)ABZSO(2) were found in milk or milk produc ts, with the exception of the milk collected 36 h after treatment in w hich 89 mu g NH(2)ABZSO(2)/kg was detected. Results indicated that ABZ was rapidly oxidized to ABZSO and then to ABZSO(2). These metabolites were found at high levels (1-4 mg/kg) in milk collected within 24 h a fter treatment. Products derived from such milk also contained high co ncentrations of the two oxidized metabolites, including up to 5 mg ABZ SO/kg in Pecorino cheese. Only small quantities of these two metabolit es were found in milk collected during the second day after treatment (range 50-500 mu g/kg). They were no longer detectable in milk collect ed during the third day after dosing; nor were they found in products made from such milli. These findings confirm that the two polar metabo lites ABZSO and ABZSO(2) were efficiently excreted from the body. Cons idering that the established maximum residue limit for ovine milk is 1 00 mu g/kg for ABZ plus its metabolites, our results confirmed the app ropriateness of the currently prescribed withdrawal time (3 d) after t he use of ABZ in lactating sheep. However, considerable levels of ABZS O were detected in milk collected within 24 h after treatment as well as in products and by-products derived from such milk. Owing to the kn own toxicity of the ABZSO, we stress the need for careful control to e nsure adherence to the prescribed withdrawal time.