title: Evaluation of an ultrafiltration-fluorescence polarization immunoassay for monitoring unbound phenytoin.
abstract: To evaluate a new ultrafiltration-fluorescence polarization immunoassay (FPIA) for monitoring blood levels of unbound phenytoin, the drug, with or without a 14C label, was added to three serum pools obtained from normal, uremic, and hypoalbuminemic patients and to 10 individual patient sera that varied greatly in phenytoin binding (11-50%). Protein-unbound phenytoin fractions were obtained from the sera by ultrafiltration using the Amicon Micropartition System and by a classic equilibrium dialysis method. The percent unbound phenytoin in each serum was determined by a radioassay and an automated FPIA (TDx System). An analysis of variance revealed no significant difference in the percent unbound phenytoin obtained at 37 degrees C by the FPIA and radioassay methods (alpha = 0.05). The data indicate that the ultrafiltration system can be combined with FPIA to produce a convenient laboratory method for routine therapeutic drug monitoring that gives results comparable to the equilibrium dialysis, radioassay reference method.
mesh_terms: D001796:Blood Protein Disorders / Q000097:blood; D005454:Fluorescence Polarization; D006801:Humans; D007118:Immunoassay; D010672:Phenytoin / Q000097:blood*; D014462:Ultrafiltration; D014511:Uremia / Q000097:blood
chemical_list: D010672:Phenytoin