Aims: To investigate the impact of cytochrome P450 2D6 (CYP2D6) on dose-adjusted serum concentrations of flupentixol, haloperidol, perphenazine and zuclopenthixol in a therapeutic drug monitoring (TDM) cohort of psychiatric patients. We also studied the functional impact of CYP2D6*41 on dose-adjusted serum concentrations in the perphenazine-treated patients.
Methods: Serum concentrations of flupentixol, haloperidol, perphenazine and zuclopenthixol from CYP-genotyped patients were extracted retrospectively from a routine TDM database in the period March 2005 to May 2019. Samples were divided into three CYP2D6 phenotype subgroups according to genotype; normal metabolizers (NMs), intermediate metabolizers (IMs) and poor metabolizers (PMs). The effect of CYP2D6 phenotype on dose-adjusted serum concentrations of the four antipsychotics was evaluated by multivariable mixed model analyses.
Results: Mean dose-adjusted serum concentrations of perphenazine (564 samples) were 3.9-fold and 1.6-fold higher in CYP2D6 PMs and IMs, respectively, compared with NMs (P < .001 and P < .01). For zuclopenthixol (658 samples), mean dose-adjusted serum concentrations were about 1.5-fold and 1.3-fold higher in CYP2D6 PMs and IMs, respectively, compared with NMs (P < .01 and P < .001). CYP2D6 was of minor or no importance to haloperidol (320 samples) and flupentixol (115 samples). In our data material, the genotype CYP2D6 *1/*41 appears to have a similar impact on dose-adjusted serum concentrations of perphenazine as *1/null (null = variant allele encoding no enzyme function).
Conclusions: This study shows that CYP2D6 is important for the metabolism of perphenazine and zuclopenthixol, but not for haloperidol and flupentixol. The CYP2D6*41 allele appears to have a reduced function close to nonfunctional variant alleles.
Keywords: CYP450; antipsychotics; genetic polymorphism; serum concentrations; therapeutic drug monitoring.
© 2020 British Pharmacological Society.