title: Instability of standard calibrators may be involved in overestimating vancomycin concentrations determined by fluorescence polarization immunoassay.
abstract: Fluorescence polarization immunoassay (FPIA) is widely used to determine serum vancomycin concentrations, and it has been shown to over-estimate vancomycin concentrations in sera from renally impaired patients. This phenomenon has generally been thought to result from interference by vancomycin crystalline degradation products (CDP-1). In this study, we confirmed that serum vancomycin concentrations in various patients determined by FPIA were higher than those determined by high-performance liquid chromatography (HPLC) or enzyme multiplied immunoassay (EMIT). However, the quantitative differences in the serum vancomycin concentrations determined by FPIA versus HPLC were higher than the CDP-1 concentrations, even when the cross-reactivity of FPIA to CDP-1 is assumed to be 100%. When the vancomycin calibrators for FPIA were stored at 4 degrees C for 30 days, their concentrations determined by FPIA and HPLC decreased by 14 and 20%, respectively, and CDP-1 corresponding to 20% of primary vancomycin was formed. When stored at 25 degrees C, the degradation of vancomycin was more marked. We concluded that not only the cross-reactivity of FPIA to CDP-1 but also the instability of calibrators may cause the overestimation of serum vancomycin concentrations determined by FPIA.
authors.affiliation: Department of Hospital Pharmacy, Kyushu University, Fukuoka, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Morishige
authors.forename: H
authors.initials: H
authors.lastname: Shuto
authors.forename: I
authors.initials: I
authors.lastname: Ieiri
authors.forename: K
authors.initials: K
authors.lastname: Otsubo
authors.forename: R
authors.initials: R
authors.lastname: Oishi
mesh_terms: D000368:Aged; D002138:Calibration; D002851:Chromatography, High Pressure Liquid; D003429:Cross Reactions; D004355:Drug Stability; D017248:Enzyme Multiplied Immunoassay Technique; D005260:Female; D016231:Fluorescence Polarization Immunoassay; D006801:Humans; D008297:Male; D008875:Middle Aged; D012015:Reference Standards; D014640:Vancomycin / Q000097:blood*
chemical_list: D014640:Vancomycin