Simultaneous quantification of cannabinoids tetrahydrocannabinol, cannabidiol and CB1 receptor antagonist in rat plasma: An application to characterize pharmacokinetics after passive cannabis smoke inhalation and co-administration of rimonabant.

A highly sensitive and selective liquid chromatography-tandem mass spectrometry method for the determination of tetrahydrocannabinol (THC), cannabidiol, and rimonabant in rat plasma was developed. Analytes and the internal standard were extracted from plasma using a combination of protein precipitation followed by liquid-liquid extraction. Chromatographic separation was done using Waters Symmetry C18, 4.6 × 150 mm, 5 um column using 10 mm ammonium formate buffer and methanol. The total run time was 6 min, and separation was achieved using isocratic elution at a flow rate of 1 mL/min using a 10:90 (aqueous: organic) ratio. The ionization of the analytes was optimized using electrospray ionization in positive mode, and multiple reaction mode was used for this analysis. This method showed linearity from 0.1 to 100 ng/ml for all the analytes and was validated according to FDA Bioanalytical Method Validation Guidance in terms of accuracy, precession, linearity, stability, matrix effect, recovery, and stability. This method was successfully applied to characterize the pharmacokinetics of THC in rats after continuous passive smoke exposure for 50 min when rimonabant was co-administered with cannabis smoke. Maximum concentration (C) for THC was observed immediately after rats were removed from the exposure chamber (10 min post completion) which declined with a terminal half-life of 3.7 h and clearance was calculated to be 1.1 (L/h). Rimonabant (i.p) at a dose of 3 mg/kg was rapidly absorbed and maximum concentration (Cmax) was seen at 11 min which declined with a terminal half-life of 5.4 h and clearance was calculated to be 2.0 (L/h). Exposure AUC (h* μg/L) for THC and rimonabant were 13.9 and 457.6 respectively. As this method was highly sensitive and required only 50 μL of plasma, it is applicable in rodent models that assess the exposure-response relationships of these drugs.