Cannabidiol and cannabidiolic acid: Preliminary in vitro evaluation of metabolism and drug–drug interactions involving canine cytochrome P‐450, UDP‐glucuronosyltransferase, and P‐glycoprotein

Abstract

Phytocannabinoid‐rich hemp extracts containing cannabidiol (CBD) and cannabidiolic acid (CBDA) are increasingly being used to treat various disorders in dogs. The objectives of this study were to obtain preliminary information regarding the in vitro metabolism of these compounds and their capacity to inhibit canine cytochrome P450 (CYP)‐mediated drug metabolism and canine P‐glycoprotein‐mediated transport. Pure CBD and CBDA, and hemp extracts enriched for CBD and for CBDA were evaluated. Substrate depletion assays using pooled dog liver microsomes showed CYP cofactor‐dependent depletion of CBD (but not CBDA) and UDP‐glucuronosytransferase cofactor‐dependent depletion of CBDA (but not CBD) indicating major roles for CYP and UDP‐glucuronosytransferase in the metabolism of these phytocannabinoids, respectively. Further studies using recombinant canine CYPs demonstrated substantial CBD depletion by the major hepatic P450 enzymes CYP1A2 and CYP2C21. These results were confirmed by showing increased CBD depletion by liver microsomes from dogs treated with a known CYP1A2 inducer (β‐naphthoflavone) and with a known CYP2C21 inducer (phenobarbital). Cannabinoid‐drug inhibition experiments showed inhibition (IC50 = 4.6–8.1 μM) of tramadol metabolism via CYP2B11‐mediated N‐demethylation (CBD and CBDA) and CYP2D15‐mediated O‐demethylation (CBDA only) by dog liver microsomes. CBD and CBDA did not inhibit CYP3A12‐mediated midazolam 1′‐hydroxylation (IC50 > 10 μM). CBD and CBDA were not substrates or competitive inhibitors of canine P‐glycoprotein. Results for cannabinoid‐enriched hemp extracts were identical to those for pure cannabinoids. These in vitro studies indicate the potential for cannabinoid–drug interactions involving certain CYPs (but not P‐glycoprotein). Confirmatory in vivo studies are warranted.

Tolerability of 2 and 4 mg/kg Dosing Every 12 Hour of a Cannabidiol- and Cannabidiolic Acid-Rich Hemp Extract on Mixed-Breed Dogs Utilized for Teaching in a Closed Colony

“…This agrees with the findings reported by Garcia et al as 3/14 dogs utilized in their study developed transient ataxia during the course of treatment with 2 mg/kg twice daily dosing of CBD/CBDA-rich hemp added to an established treatment protocol of 2 or more anti-seizure medications [8]. Both of these studies note that anti-seizure medications and CBD undergo metabolism via hepatic and gastrointestinal cytochrome p450 and hepatic conjugation activities which could alter the serum concentrations of typical anti-epileptic drugs; however, in the Garcia study, no serum alterations of phenobarbital or zonisamide were observed [8,9,21]. In a later study by Donovan et al, the interactions of CBD and phenobarbital were elegantly examined showing no influence of CBD on phenobarbital serum concentrations in normal healthy beagles at similar or higher dosing [22].…”

“…In our study, we did not see any notable alterations in CBC parameters that were related to a treatment effect; however, CBCs were not performed at each stage of the study. Repeated CBCs at each phase were not performed due to prior studies showing no alterations in any CBC parameters using doses between 5 and 10 mg/kg per day in studies examining mixed cannabinoids or CBD-rich hemp products, to date [11,21]. All of the changes over time surrounded primarily red blood cell alterations and reticulocytosis which could be related to environment change as feral dogs and treatment of GI parasitism.…”