Development and validation of a sensitive LC-MS/MS method for determination of tacrolimus on dried blood spots

A bioanalytical method for the quantification of tacrolimus (TAC) on dried blood spots (DBS) using liquid chromatography, electrospray ionization coupled with tandem mass spectrometry (LC-ESI-MS/MS) was developed and validated. It involves solvent extraction of a punch disk of DBS followed by liquid-liquid extraction. The analyte and the internal standard (IS, ascomycin) were separated on a phenyl column using an isocratic mobile phase elution at a flow rate of 0.3 mL/min. The assay was linear from 1 to 80 ng/mL. The mean recovery of TAC was 76.6%. Intra-assay, inter-assay imprecision and biases were all less than 15%. TAC on DBS was stable for at least 10 days at room temperature, and at least 24 h at 50°C. A chromatographic effect of the filter paper (Whatman 903) was not detected. The volume of blood (15-50 μL) and hematocrit of blood (ranging from 23.2 to 48.6%) did not show a significant influence on detection of TAC concentration by DBS-LC-MS/MS. Fifty samples from patients were detected by both DBS-LC-MS/MS and microparticle enzyme-linked immunoassay (MEIA). TAC concentrations measured by DBS-LC-MS/MS method tended to be lower than those by MEIA.