Diflubenzuron: intestinal absorption and metabolism in the rat

1. The metabolic fate of the insecticide diflubenzuron was investigated in the rat with radioactively labelled forms of the compound. 2. Intestinal absorption, measured as the sum of urinary and biliary excretion, diminished greatly with increasing dose, from about 50% at 4 mg/kg to about 4% at 900 mg/kg. 3. Excretion was almost complete at 72 h after dosing. At that time up to 4% of a dose was recovered from the carcasses of the rats. No detectable excretion of radioactive CO2 occurred (less than 0.5% of dose). 4. The metabolic pattern in urine and bile was investigated with diflubenzuron labelled with both 3H and 14C. No unchanged compound was detected. About 80% of the metabolites appeared to have the basic diflubenzuron structure intact. Three of these, hydroxylated at either aromatic ring, were identified; they were largely excreted as conjugates in the bile. The remainder, also largely excreted in the bile, constituted very polar material. About 20% of the diflubenzuron underwent scission of the ureido bridge. One scission product, 2,6-difluorobenzoic acid, was largely excreted as such in the urine. Its counterpart, 4-chlorophenylurea, was not present in urine or bile in appreciable quantity; nor was 4-chloroaniline detected.