In vivo pharmacokinetics of pyribenzoxim in rats

Pyribenzoxim, benzophenone O-[2,6-bis(4,6-dimethoxypyrimidin-2-yloxy)benzoyl]oxime, is a new post-emergence herbicide providing broad-spectrum weed control in rice fields. [¹⁴C]Pyribenzoxim was used to study the pharmacokinetics of the compound after oral administration of a dose of 1000mg kg^-1 to male Sprague-Dawley rats. The material balance ranged from 97.3 to 99.7% of the administered dose and urinary and fecal recovery accounted for 97.1%, with the majority of radioactivity recovered in feces (88.6%) by 168 h after treatment. Elimination as volatile products or as carbon dioxide was negligible. The following values were obtained for the compound in the blood: AUC_0-168h, 28400 μg equiv hg^-1; T_max, 12h; C_max, 372 μg equiv g^-1; half-life, 53h. Radioactivity in tissue decreased from 96.1% of applied radiocarbon at 6h to 0.4% at 168h and the highest concentration of radioactivity among the tissues was observed in liver while the lowest residues were found in brain. The elimination half-lives of radioactivity from tissues was in the range of 7 to 77h and T_max values of 12, 24 and 12h were observed for blood, liver and kidney, respectively. Except for that in the digestive tract, the tissue-to-blood ratio (TBR) was highest in the liver.