The Implications of Cytochrome P450 2D6/CYP2D6 Polymorphism in the Therapeutic Response of Atypical Antipsychotics in Adolescents with Psychosis—A Prospective Study

Background: The plasma level of antipsychotics and their metabolites depends on the activity of the cytochrome P450 (CYP) system in the liver. This research aims to test the individual response variability to atypical antipsychotic drugs, depending on the activity of the CYP2D6 enzyme. Methods: In a prospective, noninterventional study, we included 56 adolescents, 51.79% male, diagnosed with schizophrenia. The patients underwent DNA sampling for genotyping SNP by RT-PCR and CYP* allelic variants using Applied Bio-systems™ TaqMan® Assays Foster City, CA, USA). and clinical and paraclinical assessments. The effectiveness of the therapy was evaluated with the PANSS scores at baseline and 3, 6, and 12 months after the initiation of an atypical antipsychotic treatment. Results: Based on the genotyping results, the patients were divided into slow metabolizers (Group 1), extensive metabolizers (Group 2), and intermediate metabolizers (Group 3). The PANSS score showed a significant decrease in Group 2, compared to Group 3 after 3 (p = 0.02), 6 (p = 0.0009), and 12 months (p < 0.0001). The patients in Group 1 showed high PANSS scores, and those in Group 2 had fewer adverse reactions than the other groups. Conclusions: Assessing the CYP2D6 polymorphism may be useful in clinical pediatric psychiatric practice towards improving clinical results and patients’ quality of life.