Effects of neostigmine on the pharmacokinetics of intravenous parathion in rats.
It was reported that the area under the plasma concentration-time curve from time zero to time infinity (AUC) of parathion was significantly smaller and the time-averaged total body clearance (CL) of parathion was significantly faster after intravenous administration of parathion to rats pretreated with dexamethasone than those in control rats. This was supported by significantly faster intrinsic clearance of parathion to form paraoxon in hepatic microsomal fraction of rats pretreated with dexamethasone. The above data suggested that parathion was metabolized to paraoxon by dexamethasone-inducible hepatic cytochrome P450 (CYP) 3A in rats. The purpose of this study is to explain the protective effects of neostigmine against paraoxon toxicity by suppressing CYP3A and hence decreasing formation of toxic metabolite, paraoxon by neostigmine. The pharmacokinetic changes of parathion and its active metabolite, paraoxon, were investigated after intravenous administration of parathion, 3 mg/kg, to control Sprague-Dawley rats and the rats pretreated with neostigmine (200 microg/kg, intraperitoneal injection 30 min before parathion administration). After 1-min intravenous infusion of parathion to rats pretreated with neostigmine, the AUC of parathion (65.1 versus 74.3 microg min/ml) was significantly greater and the CL of parathion (45.1 versus 40.4 ml/min/kg) was significantly slower than those in control rats. Based on in vitro hepatic microsomal studies, neostigmine inhibited significantly the erythromycin N-demethylase activity (1.03 versus 0.871 nmol/mg protein/min), mainly mediated by hepatic cytochrome P450 3A in rats. The above data suggested that the formation of paraoxon was inhibited in rats pretreated with neostigmine by inhibiting CYP3A.
Hurh
E
E
College of Pharmacy, Seoul National University, Kwanak-Gu, South Korea.
Lee
E J
EJ
Kim
Y G
YG
Kim
S Y
SY
Kim
S H
SH
Kim
Y C
YC
Lee
M G
MG
D000818:Animals; D019540:Area Under Curve; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003907:Dexamethasone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007262:Infusions, Intravenous; D007306:Insecticides / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000633:toxicity; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D009388:Neostigmine / Q000494:pharmacology*; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors; D010278:Parathion / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000633:toxicity; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007306:Insecticides; D009388:Neostigmine; D010278:Parathion; D003907:Dexamethasone; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating