The Potential Role of POR*28 and CYP1A2*F Genetic Variations and Lifestyle Factors on Clozapine and N-DesmethylClozapine Plasma Levels in Schizophrenia Patients

Background: Despite its advantages over other antipsychotics, for treatment-resistant schizophrenia, clinical use of Clozapine (CLZ) is challenging by its narrow therapeutic index and potentially life-threatening dose-related adverse effects. Research design and methods: As the potential role in CLZ metabolism is assigned to CYP1A2 enzyme and consequently Cytochrome P450 oxidoreductase (POR) their genetic variations might help to determine CLZ levels in schizophrenia patients. For this purpose, 112 schizophrenia patients receiving CLZ were included in the current study. Plasma CLZ and N-desmethylclozapine (DCLZ) levels were analyzed by using HPLC and genetic variations were identified with the PCR-RFLP method. Results: The patients' CYP1A2 and POR genotypes seemed to not affect plasma CLZ and DCLZ levels whereas in the subgroup analysis, POR *28 genotype significantly influenced simple and adjusted plasma CLZ and DLCZ levels concerning smoking habit and caffeine consumption. Conclusions: The findings of the present study highlight the importance of both genetic and non-genetic factors (smoking and caffeine consumption) for the individualization of the CLZ treatment. In addition to that, it suggests that the added utility of not only the CLZ metabolizing enzymes but also POR, which is crucial for proper CYP activity, to guide CLZ dosing might be useful for clinical decision-making.

Automated summary

This study found that genetic variations in CYP1A2 and POR did not significantly affect plasma levels of Clozapine (CLZ) and N-desmethylclozapine (DCLZ). However, in the subgroup analysis, the POR*28 genotype significantly influenced CLZ and DCLZ levels in patients who smoked and consumed caffeine. Therefore, individualized treatment with CLZ should take into account both genetic and non-genetic factors.