Comprehensive Predictions of Cytochrome P450 (P450)-Mediated In Vivo Cannabinoid-Drug Interactions Based on Reversible and Time-Dependent P450 Inhibition in Human Liver Microsomes

Abstract

We previously reported the unbound reversible (IC_50,u) and time-dependent (K_I,u) inhibition potencies of cannabidiol (CBD), delta-9-tetrahydrocannabinol (THC), and THC metabolites 11-hydroxy THC (11-OH THC) and 11-nor-9-carboxy-delta-9-THC (11-COOH THC) against the major cytochrome P450 (P450) enzymes (1A2, 2C9, 2C19, 2D6, and 3A). Here, using human liver microsomes, we determined the CYP2A6, 2B6, and 2C8 IC_50,u values of the aforementioned cannabinoids and the IC_50,u and K_I,u of the circulating CBD metabolites 7-hydroxy CBD (7-OH CBD) and 7-carboxy CBD (7-COOH CBD), against all the P450s listed above. The IC_50,u of CBD, 7-OH CBD, THC, and 11-OH THC against CYP2B6 was 0.05, 0.34, 0.40, and 0.32 μM, respectively, and against CYP2C8 was 0.28, 1.02, 0.67, and 3.66 μM, respectively. 7-COOH CBD, but not 11-COOH THC, was a weak inhibitor of CYP2B6 and 2C8. All tested cannabinoids except 11-COOH THC were weak inhibitors of CYP2A6. 7-OH CBD inhibited all P450s examined (IC_50,u<2.5 μM) except CYP1A2 and inactivated CYP2C19 and CYP3A, with inactivation efficiencies (k_inact/K_I,u) of 0.10 and 0.14 minutes^-1 μM^-1, respectively. Using several different static models, we predicted the following maximum pharmacokinetic interactions (affected P450 probe drug and area under the plasma concentration-time curve ratio) between oral CBD (700 mg) and drugs predominantly metabolized by CYP3A (midazolam, 14.8) > 2C9 (diclofenac, 9.6) > 2C19 (omeprazole, 7.3) > 1A2 (theophylline, 4.0) > 2B6 (ticlopidine, 2.2) > 2D6 (dextromethorphan, 2.1) > 2C8 (repaglinide, 1.6). Oral (130 mg) or inhaled (75 mg) THC was predicted to precipitate interactions with drugs predominately metabolized by CYP2C9 (diclofenac, 6.6 or 2.3, respectively) > 3A (midazolam, 1.8) > 1A2 (theophylline, 1.4). In vivo drug interaction studies are warranted to verify these predictions. SIGNIFICANCE STATEMENT: This study, combined with our previous findings, provides for the first time a comprehensive analysis of the potential for cannabidiol, delta-9-tetrahydrocannabinol, and their metabolites to inhibit cytochrome P450 enzymes in a reversible or time-dependent manner. These analyses enabled us to predict the potential of these cannabinoids to produce drug interactions in vivo at clinical or recreational doses.

Fig. 1.

CBD and THC biotransformation pathways. Bolded enzymes are the predominant contributors (Patilea-Vrana and Unadkat, 2019; Beers et al., 2021). P450s involved in the metabolism of 7-OH CBD to 7-COOH CBD have not been identified.

Fig. 2.

Concentration-dependent inhibition of (A) CYP2B6 or (B) 2C8 activity in HLMs by CBD, 7-OH CBD, THC, or 11-OH THC and (C) concentration-dependent inhibition of CYP2C9, 2C19, 2D6, and 3A by 7-OH CBD. Of the cannabinoid tested, CBD was the most potent inhibitor of CYP2B6 and 2C8 (see Table 1). The order of 7-OH CBD inhibition potency was CYP2B6 ≈ 2C9 > 2C19 ≈ 3A > 2C8 > 2D6 (Table 1). Data shown are from a representative experiment conducted in duplicate. Solid lines represent model fit to the data.

Fig. 3.

Kinetics of time-dependent inhibition of CYP2C19 and 3A by 7-OH CBD. Estimates of k_inact and K_I, obtained by fitting appropriate equations to the k_obs data by nonlinear least-squares regression, showed that 7-OH CBD inactivated CYP2C19 and 3A with comparable efficiency (k_inact/K_I,u) but with lesser efficiency than CBD (positive control) (Table 2). Data shown are mean ± S.D. of four independent experiments, each conducted singly.