Plasma and joint tissue pharmacokinetics of two doses of oral cannabidiol oil in guinea pigs (Cavia porcellus).

Cannabidiol (CBD) has gained widespread popularity as a treatment for osteoarthritis (OA) in pets; however, there is minimal scientific evidence regarding safe and effective dosing. This study determined plasma and tissue pharmacokinetics after oral CBD oil suspension administration in Hartley guinea pigs (Cavia porcellus), which spontaneously develop OA at 3 months of age. Ten, 5-month-old, male guinea pigs were randomly assigned to receive 25 (n = 5) or 50 mg/kg (n = 5) CBD oil once orally. Blood samples were collected at 0, 0.25, 0.5, 1, 2, 4, 8, 12, and 24 h timepoints. Open-field enclosure monitoring revealed no adverse effects. After euthanasia, stifle cartilage and infrapatellar fat pads were collected to quantitate CBD. CBD concentrations were determined using a validated liquid chromatography-mass spectrometry method, and pharmacokinetic parameters were calculated using noncompartmental analysis. The area under the plasma concentration-versus-time curve was 379.5 and 873.7 h*ng/mL, maximum plasma concentration was 42 and 96.8 ng/mL, time to maximum plasma concentration was 1.6 and 4.8 h, and terminal phase half-life was 8.1 and 10.8 h for the 25 and 50 mg/kg doses, respectively. CBD was detected in joint tissues of all animals. Further studies, including work in female guinea pigs, are needed to determine the efficacy of CBD for OA.

Optimization of overhead enclosure monitoring in juvenile male Dunkin Hartley guinea pigs (Cavia porcellus).

Overhead enclosure monitoring provides objective quantitative mobility measurements for animals undergoing open-field testing. Notably, protocols for testing optimization have been minimally established for the guinea pig. It is unknown whether (a) repeated exposure, (b) time-of-day, or (c) length of testing duration influence outcome parameters. We hypothesized that guinea pigs would display decreased activity following repeated exposure to the open field; heightened activity during the earliest testing period; and that 10 min would be adequate for data collection. The study was conducted in two separate phases to distinguish between enclosure habituation and time-of-day effects, respectively. Two cohorts of male Dunkin Hartley guinea pigs were allowed voluntary movement in an open-field enclosure for 14 min to quantify mobility outcomes, including total distance traveled, total time mobile, average speed while mobile, and total time spent in the shelter. For both phases, testing occurred at four different times of day, and overhead monitoring software was programmed to divide the total testing duration into 2-min bins. Habituation phase results showed time mobile and distance traveled were influenced significantly by repeat exposure, as animals were most active during the first testing event. Time-of-day phase animals spent significantly more time mobile during the earliest testing period. Interestingly, significant differences were observed across 2-min bins for the time-of-day phase but not during the habituation phase. Specifically, progressively decreased ambulatory activity was observed as testing duration increased. Thus, habituation and time-of-day should be accounted for when possible. Finally, a trial period greater than 10 min may not yield additional data.