title: High-performance liquid chromatography-tandem mass spectrometry as a reference for analysis of tacrolimus to assess two immunoassays in patients with liver and renal transplants.
abstract: The accuracy and imprecision of three assays used for therapeutic monitoring of tacrolimus were tested using blood-containing weighed-in amounts of the drug, an enzyme-linked immunosorbent assay (ELISA), a microparticle enzyme immunoassay (MEIA I), and a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS2) assay. Accuracy was acceptable for the HPLC-MS2 assay at all concentrations tested (< 10% deviation) and for the ELISA at 1.0 and 4.0 microg/l. Accuracy was not acceptable for the ELISA at 15.0 and 50.0 microg/l or for the MEIA I at all concentrations tested. Imprecision was acceptable for the HPLC-MS2 assay at all concentrations tested (coefficient of variation < 10%), for the ELISA at 15.0 and 50.0 microg/l, and for the MEIA I at 15.0 and 50.0 microg/l. Imprecision was not acceptable for the ELISA at 1.0 and 4.0 microg/l or for the MEIA I at 1.0 and 4.0 microg/l. This assessment with weighed-in amounts of tacrolimus verified the HPLC-MS2 assay as a reference method. The performance of the two immunoassays with HPLC-MS2 was then compared in the clinical setting using blood from patients with liver (n = 30) and renal (n = 37) transplants. In the liver transplant group (127 samples), the range of tacrolimus concentrations measured by HPLC-MS2, ELISA, and MEIA I was 1.9 to 31.8, 2.1 to 35.0, and less than 0.1 to 36.5 mg/l, respectively. In the renal transplant group (129 samples), the ranges were 1.7 to 26.1, 1.9 to 24.4, and 0.9 to 28.5 microg/l, respectively. Compared with the HPLC-MS2, the ELISA had minimal bias (0.1 to 0.2 microg/l) but unacceptable variability in values (SD > 13%). The MEIA I had unacceptable bias (1.7-1.8 microg/l) and variability (SD > 23%). These data indicated that neither the ELISA nor MEIA I is interchangeable with HPLC-MS2. Moreover, in view of the current trend to reduce the therapeutic dose of tacrolimus, quantitative results using the MEIA I would not be obtainable during therapeutic drug monitoring in some patients in whom effective therapeutic concentrations can be less than 5.0 microg/l.
authors.affiliation: Department of Clinical Pharmacology, The University of Queensland, Brisbane, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Salm
authors.forename: P J
authors.initials: PJ
authors.lastname: Taylor
authors.forename: A
authors.initials: A
authors.lastname: Clark
authors.forename: G A
authors.initials: GA
authors.lastname: Balderson
authors.forename: A
authors.initials: A
authors.lastname: Grygotis
authors.forename: R L
authors.initials: RL
authors.lastname: Norris
authors.forename: S V
authors.initials: SV
authors.lastname: Lynch
authors.forename: L M
authors.initials: LM
authors.lastname: Shaw
authors.forename: S M
authors.initials: SM
authors.lastname: Pond
mesh_terms: D002851:Chromatography, High Pressure Liquid; D016903:Drug Monitoring / Q000379:methods*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007166:Immunosuppressive Agents / Q000097:blood*; D016030:Kidney Transplantation; D016031:Liver Transplantation; D013058:Mass Spectrometry; D012016:Reference Values; D016559:Tacrolimus / Q000097:blood*
chemical_list: D007166:Immunosuppressive Agents; D016559:Tacrolimus