Mitragynine and 7-hydroxymitragyine plasma pharmacokinetics in humans after single and 15 multiple oral kratom extract doses

Kratom, a medicinal Southeast Asian plant, gained interest in the US for its analgesic and stimulant effects. Previous clinical studies characterized mitragynine and 7-hydroxy-mitragynine (7-OH-MTG) plasma pharmacokinetics following kratom tea and dried kratom leaf powder intake; however, to date, there are no kratom extract data. In the current study, mitragynine and 7-OH-MTG plasma pharmacokinetics are characterized in humans following increasing single doses (SD) and fifteen multiple daily doses (MD) of concentrated kratom extract (39.5% mitragynine) containing 9.9, 29.6, and 59.2 mg mitragynine. Mean mitragynine plasma Cmax after single escalating doses increased dose-dependently, 32.8 ± 17.0, 93.2 ± 38.6 and 196 ± 77.4 ng/mL at a median Tmax of 1.3 h, with mean 7-OH-MTG Cmax of 6.8 ± 2.7, 13.7 ± 3.3 and 30.5 ± 12.2 ng/mL at a median Tmax of 1.3-1.7 h. Mean mitragynine plasma Cmax after 15 escalating multiple doses increased dose-dependently, 27.4 ± 10.9, 125 ± 79.7 and 277 ± 48.8 ng/mL at a median Tmax of 1.7-2.0 h, with mean 7-OH-MTG Cmax of 5.4 ± 1.9, 16.6 ± 6.1 and 33.9 ± 5.5 ng/mL at a median Tmax of 1.7-2.3 h. Cmax and AUC increased dose-dependently following SD and MD but were less than 1.4X greater than expected for both analytes and all doses based on strict dose proportionality. Half-lives were best reflected at higher doses due to ability to measure low analyte concentrations longer but also suggesting possible enzyme saturation. Higher 7-OH-MTG to mitragynine ratios were observed after multiple doses compared to single doses and at lower compared to higher doses. These data indicate that concentrated kratom extracts may yield greater overall mitragynine exposure than dried kratom leaf powder or kratom tea preparations administered at comparable doses.