Assessing the Pharmacokinetics and Drug Interaction Liability of Kratom, an Opioid-like Natural Product

Many patient groups often supplement their drug regimens with herbal and other natural products (NPs), raising concern for adverse NP-drug interactions. Due to a lack of rigorous guidelines for assessing the risk of NP-drug interactions, the NIH-funded Center of Excellence for Natural Product-Drug Interaction Research (NaPDI Center) was established to facilitate the identification, evaluation, and dissemination of potentially clinically relevant pharmacokinetic NP-drug interactions.Kratom is one of four high priority NPs selected by the NaPDI Center for rigorous study of drug interaction potential.

Kratom (Mitragyna speciosa) is a tree native to Southeast Asia that produces constituents with opioid-like effects. Oral supplements made from the leaves are readily available in the United States and are used for several purported medicinal benefits, such as pain relief, treatment of post-traumatic stress disorder, and management of opioid addiction. Two psychoactive constituents of the kratom leaf, mitragynine and 7- hydroxymitragynine, are believed to contribute to these effects.

Calls to poison control centers in the United States involving kratom exposures increased from 2011 to 2017 by 52-fold. More than one-third of the calls reported combined use of kratom with other substances, including opioids and benzodiazepines. In October 2017, the opioid crisis was declared a public health emergency. Many opioids are metabolized by the major drug metabolizing enzymes CYP2D6 and CYP3A4, which have been shown to be inhibited by an extract prepared from a well-characterized kratom product and purified major kratom constituents, including mitragynine and 7-hydroxymitragynine. As such, co-consuming kratom with these opioids could increase the risk of serious adverse effects via inhibition of opioid metabolism, notably respiratory depression, the primary cause of death from opioid overdose.

The purpose of this study is to assess the effects of a well-characterized kratom product on CYP2D6 and CYP3A4 activity in healthy volunteers using a cocktail approach consisting of the validated probe drugs dextromethorphan and midazolam. The primary objective is to evaluate the potential for a pharmacokinetic kratom-drug interaction with midazolam, a 'probe' drug for CYP3A4, when administered to participants previously exposed to kratom. Secondary objectives are to evaluate the pharmacokinetics of kratom constituents and the effect of kratom on the pharmacokinetics of dextromethorphan, a probe drug for CYP2D6.

Results will be used to develop physiologically-based pharmacokinetic (PBPK) models to predict the likelihood and magnitude of kratom-drug interactions, including those involving opioids. These PBPK models could be adapted to other CYP2D6 and CYP3A4 drug substrates with high abuse potential (e.g., benzodiazepines and 'Z-drugs') and used to inform the design of future kratom-drug interactions studies.

Inclusion criteria

• Not taking any medications (prescription and non-prescription) or dietary/herbal supplements known to alter the pharmacokinetics of either study drug or kratom constituents
• Willing to abstain from consuming dietary/herbal supplements, including kratom, and citrus juices for several weeks
• Willing to abstain from consuming caffeinated beverages or other caffeine-containing products the evening before and morning of the first day of a study arm
• Willing to abstain from consuming any alcoholic beverages for one day prior to any study day, during the 14-hour inpatient days, and for the 5 and/or 1 outpatient visit(s) following 14-hour visit
• Willing to use an acceptable method of contraception that does not include oral contraceptive pills or patches (such as abstinence, copper IUD, condom)
• Have the time to participate
• Are non-naïve kratom users (intermittent users who are not trying to quit but willing to abstain for several weeks)
• Carry a CYP2D6 genotype designated as having an intermediate, extensive, or ultra-extensive metabolizer phenotype
• Written informed consent (and assent when applicable) obtained from subject or subject's legal representative and ability for the subject to comply with the requirements of the study

Exclusion criteria

• Men and women under the age of 18 or over the age of 55
• Unwilling to abstain from kratom for several weeks
• Any current major illness or chronic illness such as (but not limited to) kidney disease, hepatic disease, diabetes mellitus, hypertension, coronary artery disease, chronic obstructive pulmonary disease, cancer, or HIV/AIDS
• History of anemia or any other significant hematologic disorder
• History of drug or alcohol addiction or major psychiatric illness
• A need for chronic opioid analgesics
• Use of opioid analgesics 3 weeks prior to initiation of the study
• An imminent likely need for opioid analgesics (e.g., planned dental or surgical procedure)
• Female and pregnant or nursing
• Have a history of allergy to dextromethorphan, midazolam, or related drugs
• Have a history of intolerance or allergy to kratom or opioids
• Taking concomitant medications, both prescription and non-prescription (including dietary supplements/herbal products), known to alter the pharmacokinetics of either study drug or kratom constituents
• Carry a CYP2D6 genotype designated as having a poor metabolizer phenotype
• Presence of a condition or abnormality that, in the opinion of the Investigator, would compromise the safety of the patient or the quality of the data