High performance liquid chromatography-tandem mass spectrometric assay of dexmedetomidine in plasma, urine and amniotic fluid samples for pregnant ewe model

Dexmedetomidine (DEX; Precedex^®), approved by the Food and Drug Administration (FDA) in 1999 as a sedative for use in the intensive care unit, is a potent and highly selective α₂-adrenoceptor agonist with significant sedative, analgesic and anxiolytic effects. However, the research of DEX use during pregnancy is limited and the impact of DEX on the fetal development is unclear. This article describes a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay suitable for various biomatrices of plasma, urine and amniotic fluid, as a prerequisite for pharmacokinetic characterization of DEX in the pregnant ewe model. DEX and testosterone (internal standard; IS) were extracted from 200μL of plasma, urine or amniotic fluid with ethyl acetate. The HPLC resolution was achieved on an Agilent ZORBAX SB-CN column with a gradient elution at a flow rate of 0.5mL/min using a mobile phase of 5-100% of acetonitrile with 0.5% formic acid (mobile phase B) in water (mobile phase A). The detection was performed by a triple quadrupole tandem mass spectrometer with positive electrospray ionization. The precursor/product transitions (m/z) in the positive ion mode [M+H]⁺ were m/z 201.5→95.4 for DEX and m/z 289.2→109.1 for IS. The method was validated in the concentration range of 25 (lower limit of quantification; LLOQ)-5000pg/mL for both maternal and fetal plasma, and of 50 (LLOQ)-5000pg/mL for urine and amniotic fluid, respectively. The intra- and inter-day precision and accuracy were within ±9%. The overall recoveries of DEX were 82.9-87.2%, 85.7-88.4%, 86.2-89.7% and 83.7-88.1% for maternal plasma, urine, fetal plasma and amniotic fluid, respectively. The percentage matrix factors in different biomatrices were less than 120%. Stability studies demonstrated that DEX was stable after three freeze/thaw cycles, in the autosampler tray at 20°C for 24h and during the 3h sample preparation at room temperature. The validated HPLC-MS/MS method has been successfully employed for pharmacokinetic evaluation of DEX in pregnant ewes and fetuses.