Using a stable isotope-labeled internal standard for liquid chromatography-tandem mass spectrometry quantitation of...

A sensitive and highly efficient LC-ESI-MS/MS method using a stable isotope-labeled internal standard (SIL IS) to detect meloxicam in human plasma was developed and validated. Sample preparation used only 50 μL human plasma with one-step methanol protein precipitation. A gradient mobile phase system was adopted for chromatographic separation on a Poroshell 120 SB-C₁₈ column (2.1 × 50 mm, 2.7 μm). Positive ion pattern was chosen for quantification under multiple reaction monitoring. Ion pairs were [M + H]⁺ m/z 352.1 → 115.1 for meloxicam and [M + H]⁺ m/z 355.1 → 187.1 for meloxicam-d3 (SIL IS). Total run time was 4.0 min. Standard curve was linear over a concentration range from 8.00 to 1600 ng mL^-1 . This method was fully validated to evaluate its performance, including specificity, carryover, sensitivity, linearity, accuracy, precision, recovery, matrix effects, stability, dilution reliability and incurred sample reanalysis, which provided a reliable basis for pharmacokinetic studies of meloxicam in 28 healthy Chinese volunteers. After a single-dose oral administration of 7.5 mg meloxicam, the main pharmacokinetic parameters were as follows: C_max , 814.79 ± 201.37 ng mL^-1 ; T_max , 4.54 ± 1.42 h; AUC_0-t , 24,572.04 ± 5766.93 ng·h mL^-1 ; AUC_0-∞ , 25,810.89 ± 6796.60 ng·h mL^-1 and t_1/2 , 21.11 ± 5.35 h.