Quantification of tapentadol in canine plasma by HPLC with spectrofluorimetric detection: development and validation of a new methodology.

Tapentadol (TAP) is a novel opioid pain reliever drug that is unusual in its possession of dual mechanism of action (mu opioid-receptor agonist and noradrenaline reuptake inhibitor), this feature makes the active ingredient an attractive potential progenitor of a new pharmacological class. A liquid chromatography-mass spectrometry (LC-MS) method exists to measure TAP in urine and saliva, but the aim of the present study was to develop and validate a simple HPLC-FL based method to quantify TAP in plasma. Several parameters both in the extraction and detection method were evaluated. The applicability of the method was determined by administering TAP orally to two dogs; the protocol yielded the expected pharmacokinetic results and plasma collected by jugular venipuncture at regular intervals. The mobile phase consisted of acetonitrile (A):acetic acid (B) (33 mM), delivered in gradient mode (5-95% B [0-20 min], 95-5% B [20-25 min] and finally 5% B isocratically [25-32 min]) with a flow rate of 1 mL min⁻¹. Excitation and emission wavelengths were of 273 and 298 nm, respectively. TAP was extracted from the plasma using a mixture of Et₂O:CH₂Cl₂ (7:3, v/v), which gave a recovery of 98.0-107.8% and a limit of quantification of 1 ng mL⁻¹. The chromatographic runs were specific with no interfering peaks at the retention times of the analyte and IS (O-desmethyltramadol), as confirmed by HPLC-DAD experiments. In conclusion, this was a simple and effective method using HPLC-FL to detect TAP in plasma, which may be useful for future pharmacokinetic studies.