Abstract With the highly sensitive and specific gas chromatographymass spectrometry (GC– MS), plasma concentrations resulting from an intravenous administration of only a small amount of stable isotopically labeled phenytoin (DPH-d 10) were determined to obtain information on the accurate clearance values under steady-state conditions attained with unlabeled phenytoin (DPH-d 0). A time course of DPH-d 10 concentrations was followed ...