METABOLISM OF THIABENDAZOLE IN LAYING HEN AND LACTATING GOATS

Thiabendazole (TBZ), an anthelminthic and fungicide of the benzimidazo le class, was rapidly metabolized by lactating goats and laying hens. In lactating goats dosed orally with 120 mg of [C-14]TBZ daily for 7 c onsecutive days and sacrificed at about 24 h after the final dose, an average of 74% of the total administered dose was accounted for in the matrices analyzed. Nearly all of this recovered radioactivity was fou nd in the excreta (urine, 69%; feces, 28%) with very little (less than or equal to 3%) in milk: and tissues (liver, kidney, fat; muscle). In laying hens dosed orally with 3.19 mg of [C-14]TBZ daily for 10 conse cutive days and sacrificed at about 24 h after the final dose, an aver age of about 97% of the total administered dose was accounted for in t he matrices analyzed. Nearly all (>99%) of this recovered radioactivit y was found in the excreta with very little in the eggs (similar to 0. 16%) and tissues (0.29%). Enzyme preparations (Glusulase, sulfatase, b eta-glucuronidase) and strong acid hydrolyses were used to release TBZ and its metabolites from hen and goat tissues and matrices. On the ba sis of these enzymic and acid hydrolyses, and subsequent HPLC radiochr omatographic and GC/MS analyses of the extracts, the major metabolite of TBZ in the excreta, edible tissues, milk, and eggs was determined t o be 5-hydroxythiabendazole or its O-sulfate conjugate. Minor amounts of benzimidazole and TBZ were also found in most of the goat and hen t issues examined. The results of this study show that the metabolic fat es of TBZ in lactating goats and laying hens are similar, predominantl y involving hydroxylation at the 5-position followed by sulfation.