title: Phenytoin and plasmapheresis: importance of sampling times and impact of obesity.
abstract: The effect of plasmapheresis (PP) on total and free phenytoin clearance is reported. An obese patient with the diagnosis of thrombotic thrombocytopenic purpura (TTP) was treated with PP. Twelve episodes of PP, having exchange volumes of 1.5-2.25 times the plasma volume with a mean +/- SD 7.7 +/- 0.8 L of plasma removed, were studied. A significant (p < 0.05) difference was observed with a mean change in plasma phenytoin concentrations from pre- to end-PP of 7.32 +/- 2.5 mg/L compared to 1.98 +/- 0.7 mg/L observed pre-PP to 1 h post-PP. These values corresponded to 48.4 +/- 11.6 and 15.0 +/- 6.7% decreases in phenytoin concentrations at the two aforementioned time periods. To prevent misinterpretation of plasma phenytoin concentrations, samples should not be obtained for at least 2 h after PP.
authors.affiliation: College of Pharmacy, University of Nebraska Medical Center, Omaha.
authors.forename: K M
authors.initials: KM
authors.lastname: Olsen
authors.forename: M A
authors.initials: MA
authors.lastname: Marx
authors.forename: M S
authors.initials: MS
authors.lastname: Monaghan
authors.forename: E
authors.initials: E
authors.lastname: Barnes
authors.forename: B H
authors.initials: BH
authors.lastname: Ackerman
authors.forename: A A
authors.initials: AA
authors.lastname: Pappas
mesh_terms: D001800:Blood Specimen Collection; D004830:Epilepsy, Tonic-Clonic / Q000188:drug therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000150:complications / Q000378:metabolism*; D010672:Phenytoin / Q000097:blood / Q000493:pharmacokinetics* / Q000627:therapeutic use; D010956:Plasmapheresis; D011696:Purpura, Thrombocytopenic / Q000097:blood / Q000150:complications / Q000628:therapy; D013997:Time Factors
chemical_list: D010672:Phenytoin