title: Stable-isotope methodology for the bioavailability study of phenytoin during multiple-dosing regimens.
abstract: With the highly sensitive and specific gas chromatography-mass spectrometry (GC-MS), plasma concentrations resulting from an intravenous administration of only a small amount of stable isotopically labeled phenytoin (DPH-d10) were determined to obtain information on the accurate clearance values under steady-state conditions attained with unlabeled phenytoin (DPH-d0). A time course of DPH-d10 concentrations was followed simultaneously with DPH-d0 during dosing intervals by GC-MS, with DPH-d5 as an internal standard. The present stable-isotope methodology offered advantages for the estimation of absolute bioavailability of the oral phenytoin dose in patients, while normal therapy was continued and not withdrawn.
mesh_terms: D000328:Adult; D001682:Biological Availability; D004827:Epilepsy / Q000188:drug therapy; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D010672:Phenytoin / Q000008:administration & dosage / Q000378:metabolism* / Q000652:urine; D011208:Powders; D013607:Tablets; D013810:Therapeutic Equivalency; D013997:Time Factors
chemical_list: D011208:Powders; D013607:Tablets; D010672:Phenytoin