Volumetric absorptive microsampling device (VAMS) was evaluated for bioanalysis of tacrolimus, which was used as a model drug with high blood cell partition. Aliquots of blood (ca. 10μL) with different hematocrits and fortified with tacrolimus were wicked up by VAMS and tacrolimus was extracted with a methanol-water mixture (1:1, v/v) via sonication. After chromatography on an AQUITY UPLC HSS T3 column (100×2.1 i.d., mm, 1.8μm), tacrolimus and the internal standard ascomycin, were detected in the positive ion mode with electrospray ionization by monitoring of transitions m/z 826.6→616.4 and m/z 814.6→604.0, respectively. An assay method to quantify tacrolimus from 1 to 250ng/mL in whole blood was qualified by ensuring that linearity, selectivity, intra- and inter-batch reproducibility, and stability were within the acceptance criteria. Consistent and high extraction recovery of tacrolimus was ensured from blood with low- (20%), mid- (45%), and high-hematocrit (65%) levels with minimal matrix effects. Apparent instability at ambient temperature or 4°C possibly due to reduced recovery suggests that tacrolimus in VAMS should be stored at -25°C until assay. Potential reduced recovery over time from VAMS should be taken into consideration in method optimization.
Keywords: Blood partition; LC–MS; Microsampling; Stability; Tacrolimus.
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