Cannabis is an increasingly popular recreational and medicinal drug in the USA. While cannabis is still a Schedule 1 drug federally, many states have lifted the ban on its use. With its increased u...

Awareness of drug interactions involving opioids is critical for patient treatment as they are common therapeutics used in numerous care settings, including both chronic and disease-related pain. Not only do opioids have narrow therapeutic indexes and are extensively used, but they have the potential to cause severe toxicity. Opioids are the classical pain treatment for patients who suffer from moderate to severe pain. More importantly, opioids are often prescribed in combination with multiple other drugs, especially in patient populations who typically are prescribed a large drug regimen. This review focuses on the current knowledge of common opioid drug–drug interactions (DDIs), focusing specifically on hydrocodone, oxycodone, and morphine DDIs. The DDIs covered in this review include pharmacokinetic DDI arising from enzyme inhibition or induction, primarily due to inhibition of cytochrome p450 enzymes (CYPs). However, opioids such as morphine are metabolized by uridine-5’-diphosphoglucuronosyltransferases (UGTs), principally UGT2B7, and glucuronidation is another important pathway for opioid-drug interactions. This review also covers several pharmacodynamic DDI studies as well as the basics of CYP and UGT metabolism, including detailed opioid metabolism and the potential involvement of metabolizing enzyme gene variation in DDI. Based upon the current literature, further studies are needed to fully investigate and describe the DDI potential with opioids in pain and related disease settings to improve clinical outcomes for patients. SIGNIFICANCE STATEMENT A review of the literature focusing on drug–drug interactions involving opioids is important because they can be toxic and potentially lethal, occurring through pharmacodynamic interactions as well as pharmacokinetic interactions occurring through inhibition or induction of drug metabolism.

Opioids are commonly prescribed for the treatment of chronic pain. Approximately 50% of adults who are prescribed opioids for pain co-use cannabis with their opioid treatment. Morphine is primarily metabolized by UDP-glucuronosyltransferase (UGT) 2B7 to an inactive metabolite, morphine-3-glucuronide (M3G), and an active metabolite, morphine-6-glucuronide (M6G). Previous studies have shown that major cannabis constituents including Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD) inhibit major UGT enzymes. To examine whether cannabinoids or their major metabolites inhibit morphine glucuronidation by UGT2B7, in vitro assays and mechanistic static modeling were performed with these cannabinoids and their major metabolites including 11-hydroxy-Δ⁹-tetrahydrocannabinol (11-OH-THC), 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (11-COOH-THC), 7-hydroxy-cannabidiol (7-OH-CBD), and 7-carboxy-cannabidiol (7-COOH-CBD). In vitro assays with rUGT-overexpressing microsomes and human liver microsomes showed that THC and CBD and their metabolites inhibited UGT2B7-mediated morphine metabolism, with CBD and THC exhibiting the most potent K_i,u values (0.16 µM and 0.37 µM, respectively). Only 7-COOH-CBD exhibited no inhibitory activity against UGT2B7-mediated morphine metabolism. Static mechanistic modeling predicted an in vivo drug–drug interaction between morphine and THC after inhaled cannabis, and between THC, CBD, and 7-OH-CBD after oral consumption of cannabis. These data suggest that the co-use of these agents may lead to adverse drug events in humans.

Benzodiazepines (BZDs) such as oxazepam are commonly prescribed depressant drugs known for their anxiolytic, hypnotic, muscle relaxant, and anticonvulsant effects and are frequently used in conjunction with other illicit drugs including cannabis. Oxazepam is metabolized in an enantiomeric-specific manner by glucuronidation, with S-oxazepam metabolized primarily by UGT2B15 and R-oxazepam glucuronidation mediated by both UGT 1A9 and 2B7. The goal of the present study was to evaluate the potential inhibitory effects of major cannabinoids, Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD), and major THC metabolites, 11-hydroxy-Δ⁹-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (11-COOH-THC), on the UGT-mediated metabolism of R- and S-oxazepam. The cannabinoids and metabolites were screened as inhibitors of R- and S-oxazepam glucuronidation in microsomes isolated from HEK293 cells overexpressing individual UGT enzymes (rUGTs). The IC₅₀ values were determined in human liver microsomes (HLM), human kidney microsomes (HKM), and rUGTs and utilized to estimate the nonspecific, binding-corrected K_i (K_i,u) values and predict the area under the concentration–time curve ratio (AUCR). The estimated K_i,u values observed in HLM for S- and R-oxazepam glucuronidation by CBD, 11-OH-THC, and THC were in the micromolar range (0.82 to 3.7 µM), with the K_i,u values observed for R-oxazepam glucuronidation approximately 2- to 5-fold lower as compared to those observed for S-oxazepam glucuronidation. The mechanistic static modeling predicted a potential clinically significant interaction between oral THC and CBD with oxazepam, with the AUCR values ranging from 1.25 to 3.45. These data suggest a pharmacokinetic drug–drug interaction when major cannabinoids like CBD or THC and oxazepam are concurrently administered.

Background: Morphine is a commonly prescribed opioid analgesic used to treat chronic pain. Morphine undergoes glucuronidation by UDP-glucuronosyltransferase (UGT) 2B7 to form morphine-3-glucuronide and morphine-6-glucuronide. Morphine is the gold standard for chronic pain management and has a narrow therapeutic index. Reports have shown that chronic pain patients have increasingly used other supplements to treat their chronic pain, including cannabidiol (CBD). Up to 50% of chronic pain patients report that they co-use cannabis with their prescribed opioid for pain management, including morphine. Previous work has shown that cannabidiol is a potent inhibitor of UGT2B7, including morphine-mediated metabolism. Co-use of morphine and CBD may result in unwanted drug–drug interactions (DDIs). Methods: Using available physiochemical and clinical parameters, morphine and CBD physiologically based pharmacokinetic (PBPK) models were developed and validated in both healthy and cirrhotic populations. Models for the two populations were then combined to predict the severity and clinical relevance of the potential DDIs during coadministration of both morphine and CBD in both healthy and hepatic-impaired virtual populations. Results: The predictive DDI model suggests that a ~5% increase in morphine exposure is to be expected in healthy populations. A similar increase in exposure of morphine is predicted in severe hepatic-impaired populations with an increase of ~10. Conclusions: While these predicted increases in morphine exposure are below the Food and Drug Administration’s cutoff (1.25-fold increase), morphine has a narrow therapeutic index and a 5–10% increase in exposure may be clinically relevant. Future clinical studies are needed to fully characterize the clinical relevance of morphine-related DDIs.

Hydromorphone is a highly potent opioid used to treat severe chronic pain. It is metabolized primarily by UDP-glucuronosyltransferase (UGT)2B7 to form the inactive hydromorphone-3-glucuronide. Given that previous studies have shown that the major cannabinoids, Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD), inhibit several UGT enzymes, the objective of the present study was to determine the inhibitory potential of major cannabinoids and their metabolites on UGT-mediated hydromorphone metabolism. To evaluate the potential for cannabis-induced drug interactions, cannabinoids and their metabolites were screened as potential inhibitors against hydromorphone glucuronidation in pooled human liver microsomes and microsomes from cells overexpressing recombinant UGT2B7. IC₅₀ values were determined for cannabinoids that inhibited hydromorphone glucuronidation by 50% and K_i values for those that exhibited an IC₅₀ < 100 μM in human liver microsomes. Potent inhibition of hydromorphone metabolism was observed for THC, 11-hydroxy (OH)-THC, CBD, and 7-OH-CBD, with K_i values ranging from 0.068 to 1.01 μM after correction for nonspecific cannabinoid binding. Differences in inhibition were observed for the UGT2B7^268Tyr variant compared with the wildtype UGTB7^268His isoform for several cannabinoids. Static modeling indicated that THC, 11-OH-THC, CBD, and 7-OH-CBD would result in drug interactions in vivo after inhalation and oral consumption of THC and CBD (>1.25-fold increase in hydromorphone exposure), with physiologically based pharmacokinetic predictive models indicating that CBD would cause a 20%-30% increase in hydromorphone exposure in healthy and cirrhotic individuals. These data suggest that major cannabinoids such as CBD will cause moderate drug-drug interactions with hydromorphone in humans. SIGNIFICANCE STATEMENT: This study indicates that major cannabinoids and their metabolites found in the plasma of cannabis users inhibit UGT2B7-mediated hydromorphone metabolism in vitro. It further demonstrates the potential for in vivo inhibition of hydromorphone metabolism by cannabinoids and their metabolites, indicating the potential for drug-drug interactions upon concomitant use of hydromorphone and cannabis or hydromorphone together with individual cannabinoids like Δ⁹-tetrahydrocannabinol and cannabidiol.