Bioavailability and pharmacokinetics of phenytoin during pregnancy.
Five epileptic women needing to commence phenytoin therapy during pregnancy received a single intravenous and a single oral dose of phenytoin several days apart before starting regular intake of the drug. Plasma phenytoin concentration - time data were analysed by three different pharmacokinetic techniques. However assessed, the mean oral bioavailability of the drug proved to be about 90% of the intravenous bioavailability. This finding makes it unlikely that impaired bioavailability accounts for the increase in oral phenytoin dosage necessary in pregnancy to maintain plasma phenytoin concentrations at pre-pregnancy values. Phenytoin clearance in the pregnant subjects was approximately double the published values for phenytoin clearance in non-pregnant persons. This suggests that increased (metabolic) clearance accounts for the increased phenytoin dosage requirement of pregnancy.
D000375:Aging; D001682:Biological Availability; D004827:Epilepsy / Q000188:drug therapy / Q000378:metabolism*; D005260:Female; D006801:Humans; D007700:Kinetics; D010672:Phenytoin / Q000097:blood / Q000378:metabolism* / Q000627:therapeutic use; D011247:Pregnancy; D011248:Pregnancy Complications / Q000188:drug therapy / Q000378:metabolism*
D010672:Phenytoin