BILIARY-EXCRETION OF CARBAMATE INSECTICIDES IN THE RAT

14C preparations of carbaryl, aldicarb, carbofuran, and Croneton (ethiofenfarb) were administered orally to bile-duct-cannulated rats. After 2 days, biliary radiocarbon accounted for 45.4, 28.6, 28.5, and 20.2% of the respective doses. Urinary excretion ranged from 40 to 70% of the doses, while fecal elimination did not exceed 3%. The findings indicated that oral exposure to carbamate insecticides results in an enterohepatic circulation of metabolites. Radiocarbon in the urine of carbofuran-treated rats consisted largely of sulfate and glucuronide conjugates of carbofuran hydrolytic derivatives. However, the bile contained predominantly 3-hydroxycarbofuran glucuronide, a metabolite having the carbamate ester linkage intact and one which may be cleaved to yield a potent anticholinesterase aglycone. Since enterohepatic cycling of glucuronides involves cleavage of the conjugate in the gut, biliary excretion may lead to increased systemic activity of toxic carbamate metabolites. © 1979.