Determination of tacrolimus in whole blood of pediatric liver transplant patients by UPLC-MS/MS: Informed its individualized dose.

Tacrolimus is a potent macrolide immunosuppressant widely used in pediatric liver transplant patients. However, its narrow therapeutic window and significant inter-individual pharmacokinetic differences result in a poor correlation between blood concentrations and administered doses. To support its individualized dose, a sensitive, fast and robust ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to measure tacrolimus concentrations in whole blood of pediatric liver transplant patients. The method employed acetonitrile for protein precipitation, and sample separation was achieved using an Acquity UPLC CSH C18 column (2.1 × 50 mm, 1.7 μm) with gradient elution. The mobile phase consisted of ammonium solution-water (0.5:1000, v/v) and methanol. The method demonstrated good linearity within a concentration range of 0.20-50.00 ng/mL. The intra- and inter-day precisions of tacrolimus in whole blood were less than 13.5 %, with the accuracy ranged from -7.2 % to 13.0 %. Selectivity, carryover, matrix effects, recovery, dilution reliability, and stability all met the standards set by relevant guidelines. The established UPLC-MS/MS method was successfully applied to measure the concentration of tacrolimus in the whole blood of pediatric liver transplant patients and support its individualized dose. Under the rapid UPLC-MS/MS method, 25 (65.8 %) patients required a dose increase, 3 (7.9 %) patients needed a dose reduction, and 10 (26.3 %) patients maintained their original dosage without adjustment.