title: Toxicokinetics of methyl paraoxon in the dog.
abstract: The toxicokinetics of methyl paraoxon, the active metabolite of the organophosphorus insecticide methyl parathion, were studied in non-anaesthetized dogs after intravenous (2.5 mg/kg) and oral (15 mg/kg) administration of methyl paraoxon. After intravenous administration, distribution and elimination occurred very rapidly and using the data from 5 min post-injection, the plasma concentration versus time curves could be fitted to a one-compartment open model. The mean half-life of elimination was 9.7 min, the average volume of distribution 1.76 l/kg and the average plasma clearance 126 ml/kg/min. After oral administration, peak plasma concentrations were obtained within 3-16 min, and the bioavailability varied from 5 to 71%. The hepatic extraction of methyl paraoxon measured in anaesthetized dogs, was high (70-92%). Comparison of the urinary excretion after intravenous and oral administration in two dogs indicated a gastrointestinal absorption of more than 60%. The kinetics of methyl paraoxon were linear in the dose range tested.
mesh_terms: D000284:Administration, Oral; D000818:Animals; D004285:Dogs; D005260:Female; D007275:Injections, Intravenous; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D009596:Nitrophenols / Q000652:urine; D010261:Paraoxon / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity
chemical_list: D009596:Nitrophenols; D010261:Paraoxon; C008480:methylparaoxon; C024836:4-nitrophenol