title: Covariance analysis of laboratory variance in steady-state serum phenytoin concentrations.
abstract: Inpatients (n = 57) on long term prophylaxis with 2 oral phenytoin preparations were followed up via monthly checks of serum drug concentrations. Duplicate serum aliquots were submitted to 2 laboratories, and covariance analysis was used to estimate laboratory error. The laboratory-associated variance of examinations using the 'EMIT' or 'TDX' systems was 7.1 to 10 (mg/L)2, while that of chromatographic assays was 37.1 (mg/L)2. Laboratory errors were distributed in a non-normal fashion. The ratio of the maximum rate of metabolism (Vmax) and the Michaelis-Menten constant (Km) tended to remain constant between individuals. A linear analytical model showed little more residual variance than one based on Michaelis-Menten pharmacokinetics.
authors.affiliation: Loewenstein Rehabilitation Hospital, Ra'anana, Israel.
authors.forename: H
authors.initials: H
authors.lastname: Costeff
authors.forename: Z
authors.initials: Z
authors.lastname: Groswasser
authors.forename: N
authors.initials: N
authors.lastname: Soroker
authors.forename: G
authors.initials: G
authors.lastname: van Belle
mesh_terms: D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007753:Laboratories / Q000592:standards; D008875:Middle Aged; D010672:Phenytoin / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D011786:Quality Control
chemical_list: D010672:Phenytoin