Refined Prediction of Pharmacokinetic Kratom-Drug Interactions: Time-Dependent Inhibition Considerations

Preparations from the leaves of the kratom plant (Mitragyna speciosa) are consumed for their opioid-like effects. Several deaths have been associated with kratom used concomitantly with some drugs. Pharmacokinetic interactions are potential underlying mechanisms of these fatalities. Accumulating in vitro evidence has demonstrated select kratom alkaloids, including the abundant indole alkaloid mitragynine, as reversible inhibitors of several cytochromes P450 (CYPs). The objective of this work was to refine the mechanistic understanding of potential kratomdrug interactions by considering both reversible and timedependent inhibition (TDI) of CYPs in the liver and intestine. Mitragynine was tested against CYP2C9 (diclofenac 4'-hydroxylation), CYP2D6 (dextromethorphan O-demethylation), and CYP3A (midazolam 1'-hydroxylation) activities in human liver microsomes (HLMs) and CYP3A activity in human intestinal microsomes (HIMs). Comparing the absence to presence of NADPH during preincubation of mitragynine with HLMs or HIMs, an similar to 7-fold leftward shift in IC50 (similar to 20 to 3 mu M) toward CYP3A resulted, prompting determination of TDI parameters (HLMs: K-l, 4.1 +/- 0.9 mu M; k(inact), 0.068 +/- 0.01 min(-1); HIMs: K-l, 4.2 +/- 2.5 mu M; k(inact), 0.079 +/- 0.02 min(-1)). Mitragynine caused no leftward shift in IC50 toward CYP2C9 (similar to 40 mu M) and CYP2D6 (similar to 1 mu M) but was a strong competitive inhibitor of CYP2D6 (K-l, 1.17 +/- 0.07 mu M). Using a recommended mechanistic static model, mitragynine (2-g kratom dose) was predicted to increase dextromethorphan and midazolam area under the plasma concentration-time curve by 1.06- and 5.69-fold, respectively. The predicted midazolam area under the plasma concentration-time curve ratio exceeded the recommended cutoff (1.25), which would have been missed if TDI was not considered. SIGNIFICANCE STATEMENT Kratom, a botanical natural product increasingly consumed for its opioid-like effects, may precipitate potentially serious pharmacokinetic interactions with drugs. The abundant kratom indole alkaloid mitragynine was shown to be a time-dependent inhibitor of hepatic and intestinal cytochrome P450 3A activity. A mechanistic static model predicted mitragynine to increase systemic exposure to the probe drug substrate midazolam by 5.7-fold, necessitating further evaluation via dynamic models and clinical assessment to advance the understanding of consumer safety associated with kratom use.

Automated summary

Kratom's main alkaloid mitragynine has been shown to be a time-dependent inhibitor of hepatic and intestinal cytochrome P450 3A activity, potentially causing serious pharmacokinetic interactions with drugs. A static model predicted that mitragynine would increase systemic exposure to the probe drug midazolam by approximately 5.7-fold.