MDMA, methamphetamine, and CYP2D6 pharmacogenetics: what is clinically relevant?

Area of Science:

• Pharmacology
• Drug Metabolism
• Clinical Significance

Background:

• The polymorphic cytochrome P450 isozyme CYP2D6 is central to the in vitro metabolism of amphetamine-like psychostimulants.
• Methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) are archetypal compounds with high abuse prevalence and differential CYP2D6 interactions.

Purpose of the Study:

• To investigate the translation of in vitro findings to in vivo outcomes for methamphetamine and MDMA metabolism.
• To assess the clinical significance of CYP2D6 polymorphism in the context of these psychostimulants.

Main Methods:

• Comparative analysis of methamphetamine (weak substrate/inhibitor) and MDMA (high-affinity substrate/potent mechanism-based inhibitor) interactions with CYP2D6.
• Evaluation of the contribution of CYP2D6 to the overall metabolic clearance of these drugs in vivo.
• Consideration of alternative metabolic pathways, including other cytochrome P450 isoenzymes and renal excretion.

Main Results:

• The fraction of metabolic clearance attributed to CYP2D6 for both methamphetamine and MDMA is considerably lower in vivo than predicted by in vitro data.
• MDMA's mechanism-based inhibition effectively phenocopies all subjects to the poor metabolizer phenotype, regardless of genotype.
• Other cytochrome P450 isoenzymes and renal excretion significantly contribute to the clearance of both compounds.

Conclusions:

• The clinical relevance of CYP2D6 polymorphism for methamphetamine and MDMA is less pronounced than initially suggested by in vitro studies.
• A multifactorial clearance mechanism involving multiple enzymes and excretion routes modulates the in vivo impact of CYP2D6 activity.