COMPARISON OF GENTAMICIN PHARMACOKINETIC PARAMETERS DETERMINED BY FLUORESCENCE POLARIZATION IMMUNOASSAY AND LATEX AGGLUTINATION METHODS

Fluorescence polarization immunoassay (FPIA) (TDx, Abbott Laboratories Diagnostics, Irvin, TX, U.S.A.) is commonly utilized for quantitative determination of gentamicin serum concentrations. Recently, automated homogeneous latex agglutination (LA) (Technicon Immuno-1, Miles Diagn ostics Division, Tarrytown, NY, U.S.A.) for the quantitative determina tion of gentamicin serum concentrations has been approved for commerci al use. The purpose of this study was to determine whether gentamicin serum concentration-time data from the same patients assayed by FPIA a nd LA would produce the same estimates for half-life, elimination rate constant, distribution volume, drug clearance, dosage interval, and d ose. A total of 70 pre- and postinfusion serum samples were obtained f rom 19 patients. Each sample was divided into two aliquots; one was as sayed by FPIA and the other by LA. The correlation coefficient between the two assay methods was 0.99 (y = 1.03x - 0.05). The mean differenc es for half-life, volume of distribution. elimination rate constant, t otal body clearance, and gentamicin dosage were 0. 13, 0.32, 0.66, - 0 .99, and 0.03%, respectively. No statistically significant differences were seen in calculated gentamicin pharmacokinetic parameters (p < 0. 05). Pharmacokinetic parameters and dosage recommendations derived fro m FPIA and the LA assay using pre- and postinfusion serum concentratio n-time data appear interchangeable and do not result in differences be tween gentamicin dosing regimens.