The Impact of CYP2D6 metabolizer phenotypes on the EDDP/methadone metabolic ratio: A comprehensive analysis

Methadone is a synthetic opioid that is often used for prevention of withdrawal symptoms and for management of chronic pain. In concentrations above the therapeutic level however, methadone can lead to detrimental side effects, such as respiratory depression. Several cytochrome P450 (CYP) enzymes are involved in methadone metabolism, foremost in building the main metabolite 2-ethylidene-1,5-dimethyl-3,3diphenylpyrrolidine (EDDP). It is well known that genetic polymorphisms within the CYPs can lead to an altered metabolism, affecting methadone elimination and peak concentrations. The metabolic ratio, in forensic toxicology suggested to assist in distinguishing between chronic and acute intake, can also be affected by genetic variations in CYP genes. The aim of the study was therefor to examine, whether the metabolizer type of CYP2D6, CYP2C19 and CYP2B6 can be associated with a certain type of intoxication, methadone concentration or metabolic ratio in postmortem blood samples of methadone intakers. The metabolic ratio of EDDP/methadone was determined in 37 blood samples from deceased methadone intakers in 2023. These cases were genotyped for CYP2D6, CYP2C19 and CYP2B6 via SNaPshot analysis. In case of CYP2D6 a copy number variations analysis was applied using qPCR. Metabolizer phenotypes were determined according to guidelines by the Dutch Pharmacogenetics Working Group (DPWG) and the Clinical Pharmacogenetics Implementation Consortium (CPIC). Our results show a significantly increased metabolic ratio of EDDP/methadone in the CYP2D6 intermediate metabolizer (IM) group, compared to the CYP2D6 normal metabolizer (NM) group. Further, when separating the methadone intakers by type of intoxication, CYP2D6 IM had a significantly higher metabolic ratio in the mix intoxication and the non-intoxication group compared to NM, poor and ultrarapid metabolizers (PM, UM).