title: Determination of blood sirolimus concentrations in liver and kidney transplant recipients using the Innofluor fluorescence polarization immunoassay: comparison with the microparticle enzyme immunoassay and high-performance liquid chromatography-ultraviolet method.
abstract: BACKGROUND
  Although high-performance liquid chromatography (HPLC) is the method of choice for blood sirolimus determination, the microparticle enzyme immunoassay (MEIA) run on the IMx analyser is widely used in therapeutic monitoring of this immunosuppressant agent. The aim of our study was to evaluate the possible determination of sirolimus using the fluorescence polarization immunoassay (FPIA) commercialized for everolimus quantification.
  
  
  METHODS
  Sirolimus concentrations were determined in whole-blood samples from liver and kidney transplant recipients using the Innofluor Certican FPIA (Seradyn Inc.) run on a TDx analyser (Abbott Laboratories), Sirolimus MEIA run on an IMx analyser (Abbott Laboratories), and HPLC (UV detection) methods.
  
  
  RESULTS
  The Innofluor FPIA has a similar cross-reactivity with everolimus and sirolimus, and the within- and between-run coefficients of variation obtained for sirolimus determination were 2.7%-13.3%. In analysing different blood samples from liver and kidney transplant patients the linear regressions obtained were: FPIA = 1.12 HPLC + 0.43 (n=104, r=0.874), MEIA = 1.14 HPLC (n=146, r=0.892), and FPIA = 1.00 MEIA + 0.29 (n=106, r=0.941). Better correlation coefficients were obtained between the methods in the liver transplant samples (r>or=0.900) than in the kidney transplant samples (r>or=0.849). No significant effect was found for sirolimus clearance or the blood hematocrit on the relationship between the results produced by both immunoassays and HPLC.
  
  
  CONCLUSIONS
  The Innofluor FPIA is a valid alternative with an analogous performance to the MEIA for the therapeutic monitoring of sirolimus.
authors.affiliation: Unidad Monitorización Fármacos, Laboratorio Central, Hospital Clinico Universitario, Santiago de Compostela, Spain.
authors.forename: Lorena
authors.initials: L
authors.lastname: Bouzas
authors.forename: Jesús
authors.initials: J
authors.lastname: Hermida
authors.forename: J Carlos
authors.initials: JC
authors.lastname: Tutor
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D016231:Fluorescence Polarization Immunoassay / Q000379:methods*; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods*; D007166:Immunosuppressive Agents / Q000097:blood*; D016030:Kidney Transplantation; D016031:Liver Transplantation; D010316:Particle Size; D015203:Reproducibility of Results; D020123:Sirolimus / Q000097:blood*; D013056:Spectrophotometry, Ultraviolet / Q000379:methods*
chemical_list: D007166:Immunosuppressive Agents; D020123:Sirolimus