RT Journal Article SR Electronic T1 Numerical Analysis of Time Dependent Inhibition by MDMA JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP dmd.119.089268 DO 10.1124/dmd.119.089268 A1 John T. Rodgers A1 Jeffrey P. Jones YR 2019 UL http://dmd.aspetjournals.org/content/early/2019/10/22/dmd.119.089268.abstract AB Methylenedioxymethamphetamine (MDMA) is a known drug of abuse and schedule 1 narcotic under the Controlled Substances Act. Previous pharmacokinetic work on MDMA used classical linearization techniques to conclude irreversible mechanism-based inhibition of CYP2D6. The current work challenges this outcome by assessing the possibility of two alternative reversible kinetic mechanisms known as the quasi-irreversible (QI) and equilibrium (EM) inhibition models. In addition, progress curve experiments were used to investigate the residual metabolism of MDMA by liver microsomes and 2D6 baculosomes over incubation periods up to 30 minutes. These experiments revealed activity in a terminal linear phase at the fractional rates with respect to initial turnover of 0.0354 ± 0.0089 in HLM and 0.0114 ± 0.0025 in baculosomes. Numerical model fits to percent-remaining-activity (PRA) data were consistent with progress curve modeling results, wherein an irreversible inhibition pathway was found unnecessary for good fit scoring. Both QI and EM kinetic mechanisms fit the PRA data well, although in 2D6 baculosomes the inclusion of an irreversible inactivation pathway did not allow for convergence to a reasonable fit. The kinetic complexity accessible to numerical modeling has been used to determine that MDMA is not an irreversible inactivator of CYP2D6, and instead follows what can be generally referred to as slowly-reversible inhibition.SIGNIFICANCE STATEMENT The work herein describes usage of computational tools to delineate between irreversible and slowly reversible time dependent inhibition. Such tools are used in the paper to analyze MDMA and classify it as a reversible time dependent inhibitor.