Advancing Personalized Medicine in Psychiatry: A Descriptive Pilot Study Integrating Pharmacogenetics and Pharmacokinetics in Long-Acting Antipsychotic Treatment

Abstract

Background: Personalized precision medicine adapts therapeutic strategies to individual characteristics. In psychiatry, suboptimal outcomes with antipsychotics are often related to adverse drug reactions, poor adherence and therapeutic failure. Pharmacogenetics, particularly CYP2D6 genotyping, can improve clinical outcomes through genotype-guided therapy. This study aimed to design and implement a pharmacogenomic and pharmacokinetic testing program for long-acting injectable (LAI) antipsychotics within the Galician Health Service to enhance personalized psychiatric care. Methods: The pilot program encompasses pharmacogenetic and pharmacokinetic testing. Inclusion criteria were broad, covering patients initiating or receiving LAI antipsychotic therapy, as well as those with prior adverse reactions in order to explore scenarios where pharmacogenetic and/or pharmacokinetic data could help with clinical decisions. Structured workflows, interdisciplinary training and integration of results into the electronic health record supported implementation. A pharmacogenetic panel was specifically designed for psychiatric care, targeting clinically relevant variants in CYP2D6, CYP3A4 and ABCB1. Results: A total of 540 patients were included, with primary testing reasons being clinical follow-up (54.6%) and oral-to-LAI transition (38.5%). The CYP2D6 phenotypes were 55% normal, 34% intermediate, 6.3% poor and 4.3% ultrarapid metabolizers. Atypical metabolism was observed in 6.7% of patients for CYP3A4 and in over half for ABCB1. Plasma drug levels were within the therapeutic range for most patients, though some measurements were above or below expected values. Conclusions: This pilot demonstrates a scalable, evidence-based approach to precision psychiatry for LAI antipsychotics, integrating pharmacogenetic and pharmacokinetic testing into routine care. The framework facilitates genotype-guided decision-making and supports broader adoption of pharmacogenomics in psychiatric practice.