A discordance between cytochrome P450 2D6 genotype and phenotype in patients undergoing methadone maintenance treatment

Aims To assess CYP2D6 activity and genotype in a group of patients undergoing methadone maintenance treatment (MMT). Methods Blood samples from 34 MMT patients were genotyped by a polymerase chain reaction-based method, and results were compared with CYP2D6 phenotype (n = 28), as measured by the molar metabolic ratio (MR) of dextromethorphan (DEX)/dextrorphan (DOR) in plasma. Results Whereas 9% of patients (3/34) were poor metabolizers (PM) by genotype, 57% (16/28) were PM by phenotype (P