Contribution of cytochrome P450 2D6 to 3,4- methylenedioxymethamphetamine disposition in humans : Use of paroxetine as a metabolic inhibitor probe

3,4-Methylenedioxymethamphetamine (MDMA) is a synthetic amphetamine derivative typically used for recreational purposes. The participation of cytochrome P450 (CYP) 2D6 in the oxidative metabolism of MDMA may suggest an increased risk of acute toxicity in CYP2D6 poor metabolisers. This study was aimed at assessing the contribution of CYP2D6 to MDMA disposition in vivo using paroxetine as a metabolic probe inhibitor. Paroxetine, a CYP2D6 inhibitor, was repeatedly administered before MDMA administration. This was a randomised, double-blind, crossover, placebo-controlled trial conducted in seven healthy male volunteers who were CYP2D6 extensive metabolisers. Treatment conditions (paroxetine/MDMA and placebo/MDMA) were randomly assigned. Each volunteer participated in two 3-day sessions. On days 1, 2 and 3 subjects received a single oral dose of paroxetine or placebo 20 mg. On the third day, a single oral dose of MDMA 100 mg was administered in both paroxetine and placebo conditions. Plasma concentration-time profiles and urinary recoveries of MDMA and its metabolites were measured, as well as plasma concentrations of paroxetine, (3S,4R)-4-(4-fluorophenyl)-3-(3,4-methylenedioxyphenoxymethyl)-piperidine, and (3S,4R)-4-(4-fluorophenyl)-3-(3-methoxy-4-hydroxyphenoxymethyl)-piperidine (HM-paroxetine). Paroxetine given before MDMA resulted in significant increases of MDMA area under the plasma concentration-time curve from 0 to 27 hours (AUC(27)) [23%], AUC from zero to infinity (AUC(infinity)) [27%] and maximum plasma concentration (C(max)) [17%], without significant differences in MDMA time to reach C(max) (t(max)). MDMA elimination-related pharmacokinetic parameters showed a significant reduction of MDMA elimination rate constant (K(e)) [-14%] and plasmatic clearance (CL(P)) [-29%]. In the case of 3,4-dihydroxymethamphetamine (HHMA), a 21% decrease in C(max) with no significant differences in AUC(27), AUC(infinity), K(e) and elimination half-life) were found. 4-Hydroxy-3-methoxymethamphetamine (HMMA) showed a decrease in plasma concentrations with a reduction in AUC(27) (-28%), AUC(infinity) (-20%) and C(max) (-46%). In the case of 3,4-methylenedioxyamphetamine (MDA) an increase in C(max) (17%) and AUC(27) (16%) was found. Following paroxetine pretreatment, the urinary recovery (0-45 hours) of MDMA increased by 11%; HHMA and HMMA urinary recoveries were 27% and 16% lower, respectively compared with placebo. The ratio of C(max) values of paroxetine and its metabol