ABSORPTION, TISSUE DISTRIBUTION, EXCRETION, AND METABOLISM OF H-3-LABELED AND C-14-LABELED EMAMECTIN BENZOATE IN RATS

Male and female rats were administered a single high (20 mg/kg, oral) or low (0.5 mg/kg, oral or intravenous) dose of radiolabeled 4 ''-deox y-4 ''-(epi-methylamino)avermectin B-1a (MAB(1a)) benzoate. The bioava ilability of MAB(1a) benzoate (low dose) in male and female rats was 4 3% and 63%, respectively. More than 98% of the total radioactivity was found in feces, with <0.4% in urine and <1.6% in the tissues. The tot al radioactive residues (TRR) in feces and tissues consisted of MAB(1a ) and a single N-demethylated metabolite. The TRR contents (ppb parent equivalent) of kidney, liver, fat, muscle, spinal cord, and brain at day 1 post low oral dose in male rats were 437, 355, 241, 109, 30, and 8 ppb, respectively, and in female rats 260, 244, 192, 90, 11, and 5 ppb, respectively. The TRR contents of these tissues from both male an d female rats declined to very low levels (less than or equal to 12 pp b) by day 7. The TRR content of tissues at day 7 post high dose was re latively high (8-2033 ppb). Lung and spleen had higher residue content s in comparison to other tissues. Daily pretreatment with the compound for 14 days had no effect on the tissue residue levels and metabolism .