Pharmacokinetic Evaluation of a Cannabidiol Supplement in Horses

Cannabidiol (CBD) products have gained popularity among horse owners despite limited evidence regarding pharmacokinetics. The purpose of this study was to describe the pharmacokinetic profile of multiple doses of an orally administered cannabidiol product formulated specifically for horses. A randomized 2-way crossover design was used. Seven horses received 0.35 or 2.0 mg/kg CBD per os every 24 hours for 7 total doses, separated by a 2-week washout. Plasma CBD and delta-9-tetrahydrocannabinol (THC) were quantified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) daily through day 10, then on day 14 after beginning CBD administration. On the final day of CBD administration, plasma CBD and THC were quantified at multiple times. After administration of 0.35 mg/kg of CBD, the C_max of CBD was 6.6 ± 2.1 ng/mL while T_max was 1.8 ± 1.2 hour, whereas the C_max for THC was 0.7 ± 0.6 ng/mL with a T_max of 2.5 ± 1 hour. After administration of 2.0 mg/kg of CBD, the C_max of CBD was 51 ± 14 ng/mL with a mean T_max of 2.4 ± 1.1 hour and terminal phase half-life of 10.4 ± 6 hour, whereas the C_max of THC was 7.5 ± 2.2 ng/mL with a T_max of 2.9 ± 1.1 hour. Oral administration of a cannabidiol product at 0.35 mg/kg or 2.0 mg/kg once daily for 7 days was well-tolerated. Based on plasma CBD levels obtained, dose escalation trials in the horse evaluating clinical efficacy at higher mg/kg dose rates are indicated.