A sensitive bioanalytical method for quantitative determination of resiniferatoxin in rat plasma using ultra-high performance liquid chromatography coupled to tandem mass spectrometry and its application in pharmacokinetic study.

Resiniferatoxin (RTX) is a daphnane diterpene isolated from the latex of Euphorbia resinifera O. Berg, a potent activator of transient receptor potential vanilloid 1 (TrpV1), with a potency 10-10 times greater than pure capsaicin. Intravenous administration of RTX at very low concentration improves urodynamic parameters in patients with neurogenic detrusor overactivity and also reduces bladder pain in patients. Herein, a simple, rapid, selective and sensitive method for determination of RTX with silydianin as an internal standard was developed using ultra-high performance liquid chromatography coupled to tandem mass spectrometry with electrospray ionization source (UHPLC-ESI-MS/MS) in multiple reaction monitoring mode. The mass spectrometer was operated in positive electrospray ionization ((+) ESI) mode. Multiple reaction monitoring (MRM) mode was performed with ion pairs of m/z: 629.23→283.2 for RTX and 483.24→153.1 for IS. The limit of detection achieved in this method for RTX was 0.05 ng/mL and had good linearity in calibration range of 0.2-50 ng/mL ( r = 0.99). Precision and accuracy values were found to be < 15% (within acceptable limit), extraction recovery (≥ 88.2%), matrix effect (≥ 89.7%) and stability were in accordance with the bioanalytical guidelines. The sensitivity of this bio-analytical method supported the successful pharmacokinetic evaluation of RTX on rat plasma (2.5 μg/kg dose; i.v.) and has demonstrated pharmacokinetic parameters V and AUC as 191.0 ± 71.31 mL/kg and 981.6 ± 137.40 min*ng/mL, respectively. The clearance was found to be 2.6 ± 0.38 mL/min/kg and half-life was 53.6 ± 23.51 min. This efficient, rapid and reliable method promises the quantification at low concentration of RTX, allowing determination of the pharmacokinetic profile, which is essential in future drug delivery and clinical application.