Determination of dexmedetomidine using high performance liquid chromatography coupled with tandem mass spectrometric (HPLC-MS/MS) assay combined with microdialysis technique: Application to a pharmacokinetic study.

Dexmedetomidine, as a safe sedative, mainly exerts on the central nervous system particularly in the locus coeruleus producing arousable sedation with potential analgesic and anxiolytic effects. The quantification and pharmacokinetic investigation of dexmedetomidine in the central nervous system have been described rarely. In order to estimate the unbound dexmedetomidine concentrations in brain extracellular fluid and blood simultaneously, we employed microdialysis technique as a sampling method and primarily established a rapid, sensitive and selective high-performance liquid chromatography coupled with tandem mass spectrometry method (HPLC-MS/MS). Dexmedetomidine and the internal standard (dexmedetomidine-d4) were extracted in liquid-liquid extraction procedure with ethyl acetate from 10 μL of alkalinized microdialysate sample. After evaporation under nitrogen at room temperature, the analytes were reconstituted in acetonitrile and transferred to be detected. HPLC was performed on an Agilent Poroshell 120 Hilic column (4.6 × 100 mm, 2.7 μm) with isocratic elution at a flow rate of 0.3 mL/min by 0.1% formic acid/acetonitrile (60:40, v/v). The detection was performed on a triple quadrupole tandem mass spectrometer in the multiple reaction monitoring (MRM) mode using the respective [MH] ions m/z 201.2 to m/z 95.1 for DEX and m/z 205.2 to m/z 99.1 for IS (DEX-d4). The concentration-response relationship was of good linearity over a concentration range of 1.00-1000.00 ng/mL with the correlation coefficient above 0.999. The lower limit of quantification was 1.00 ng/mL with a relative standard deviation of less than 20%. The intra- and inter-day accuracy were within ±5.00% and precision was <7.23%. The recoveries of dexmedetomidine in microdialysates were 76.61-93.38%. The validated HPLC-MS/MS method has been successfully applied to study the pharmacokinetics of dexmedetomidine in rats after a caudal vein administration.