Quantification of 11 kratom alkaloids including mitragynine and its main metabolites in human plasma using LC-MS/MS

Recently in the USA, kratom consumers increasingly report use of the plant for self-treatment of mood ailments, the lack of energy, chronic pain, and opioid withdrawal and dependence. Several alkaloids are present in kratom leaves, but limited data are available on their pharmacokinetics/pharmacodynamics, except for mitragynine. To support clinical studies, a high-performance liquid chromatography-tandem mass spectrometry assay for the simultaneous quantification of 11 kratom alkaloids in human plasma was developed and validated. For calibration standards and quality control samples, human plasma was fortified with alkaloids at varying concentrations, and 200 µL were extracted employing a simple one-step protein precipitation procedure. The extracts were analyzed using LC-MS/MS including electrospray ionization (ESI) in positive multiple reaction monitoring (MRM) mode. The lower limit of quantification was 0.5 ng/mL, and the upper limit of quantification was 400 ng/mL for all analytes. Inter-day analytical accuracy and imprecision ranged from 98.4 to 113% of nominal and from 3.9 to 14.7% (coefficient of variance), respectively. The analysis of plasma samples collected during a clinical trial administering capsules containing kratom leaf extract showed that most samples had quantifiable concentrations of mitragynine, 7-OH-mitragynine, speciogynine, speciociliatine, and paynantheine and that mitragynine, speciogynine, and speciociliatine accumulated in human plasma after daily administration over 15 days. An LC-MS/MS assay for the specific quantification of kratom alkaloids including mitragynine and its main metabolites was developed and successfully validated in human plasma. Human plasma samples collected following multiple oral administrations of a controlled Kratom extract documented accumulation of kratom alkaloids over 15 days.