Background and objective: 3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) is a ring-substituted amphetamine widely used for recreational purposes. MDMA is predominantly O-demethylenated in humans by cytochrome P450 (CYP) 2D6 and is also a potent mechanism-based inhibitor of the enzyme. This study assessed the inhibition and recovery half-life of CYP2D6 and CYP3A4 activity in female subjects by administering the probe drug dextromethorphan before and repeatedly after MDMA administration. These data were compared with the data obtained from a previous study in male subjects.
Study design: Twelve healthy female subjects who were CYP2D6 extensive metabolizers participated as outpatients in two experimental sessions. Session 1 was conducted over 2 days and session 2 over 10 days, with a minimum of 3 days between sessions. In session 1, subjects received a single oral dose of dextromethorphan 30 mg. In session 2, a 1.5 mg/kg MDMA dose was given at 0 hours, followed at 4 hours by repeated 30 mg doses of dextromethorphan over the next 10 days.
Methods: Plasma concentration-time profiles and urinary recoveries of dextromethorphan and its metabolites dextrorphan (DOR), 3-methoxymorphinan (MM) and hydroxymorphinan-3-ol (HM) were measured.
Results: MDMA given prior to dextromethorphan resulted in a 10-fold increase in the dextromethorphan maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC), with corresponding decreases in DOR and HM pharmacokinetic parameters. The mean ± SD C(max) of MDMA was 188.8 ± 16.7 ng/mL, with a time to reach C(max) (t(max)) of 2.0 ± 0.4 hours and an AUC from 0 to 25 hours of 2645.2 ± 170.9 mg · h/mL. The urinary recovery of the dextromethorphan dose as dextromethorphan and its main metabolites was 25.4 ± 8.9% with no MDMA pretreatment versus 6.6 ± 1.1% after 1.5 mg/kg of MDMA (p = 0.0001). The metabolic ratio (MR) increased almost 60-fold from 0.018 ± 0.028 to 0.998 ± 0.932 after MDMA administration, with 100% of the subjects having a value greater than the antimode of 0.3 that signified the poor-metabolizer phenotype. Data analysis of results obtained in the present study compared with those from a previous study in male subjects showed significant differences in the dextromethorphan/DOR MR in the 0- to 8-hour (session 1) and 4- to 12-hour (session 2, post MDMA) collection periods (p = 0.032 and p = 0.01, respectively). CYP2D6 activity recovered after 10 days to 90% of baseline activity, with a recovery half-life of 36.6 ± 22.9 hours. Male subjects showed a shorter recovery half-life (27.6 ± 25.1 hours). The measurement of CYP3A4 activity indicated a non-significant increase in C(max) and AUC values of MM after drug intake, but urinary data reflected significant differences in dextromethorphan/MM MR in both sexes, although the difference was more pronounced in women. Dextromethorphan/MM MR increased almost 3-fold from baseline.
Discussion and conclusion: In women the pretreatment with MDMA resulted in a decrease in dextromethorphan clearance. CYP2D6 activity recovered after 10 days to 90% of baseline activity. Regarding CYP3A4 activity, there is an apparent decrease in its activity after MDMA use. In women, MDMA use has been associated with psychiatric symptoms and psychological problems that may require psychopharmacological treatment with antidepressant drugs, some of which are known CYP2D6 substrates. MDMA-induced mechanism-based inhibition of CYP2D6 is of relevance, and physicians should be advised to prescribe medications whose metabolic disposition is not regulated by CYP2D6.