Pharmacogenetics and Therapeutic Drug Monitoring of Fluoxetine in a Real-World Setting: A PK/PD Analysis of the Influence of (Non-)Genetic Factors

This work presents the GnG-PK/PD-AD study-a pharmacokinetics/pharmacodynamics (PK/PD) analysis of the impact of genetic and nongenetic factors on the treatment with the antidepressant fluoxetine (FLU)-with a focus on potential biomarkers. Seventy-nine depressed patients treated with FLU were recruited and clinically characterized in the scope of the study. Clinical outcomes, including remission and antidepressant adverse effects were assessed by means of the Hamilton Depression Rating Scale and the Antidepressant Side-Effect Checklist, respectively. Patients were submitted to therapeutic drug monitoring of FLU and norfluoxetine and genotyping of the CYP2C9, CYP2C19, CYP2D6, and ABCB1 genes. A multivariate analysis was used to evaluate the impact of genetic and nongenetic factors on the drug plasma concentrations and clinical outcomes and to identify potential biomarkers. Genetically determined CYP2D6 activity was found to be a predictor of FLU and norfluoxetine concentrations (p < .05). In turn, genetic and nongenetic factors related to CYP2D6 and P-glycoprotein were found as potential biomarkers of the clinical outcomes of FLU (p < .05). Specifically, the potential of the CYP2D6 to be inhibited by drug-induced phenoconversion was associated with a higher severity of depression (p < .05). Moreover, ABCB1 TTT-haplotype was favorable to better clinical outcomes with FLU (higher likelihood of remission and lower severity of adverse effects; p < .05). The potential of the P-glycoprotein to be inhibited by drug-induced phenoconversion was also related to a worse tolerability profile (higher severity and number of adverse effects; p < .05). Lastly, the presence of nervous system comorbidities was associated with a higher severity of adverse effects and aging and the female gender with a higher severity of depression and lower probability of remission (p < .05). Public Health Significance Fluoxetine (FLU) is one of the first-line approaches for the treatment of depression; however, like other antidepressant drugs, it has been associated with substantial variability in the clinical outcomes. The present work supports that this variability is frequently associated with specific genetic and nongenetic factors and identifies potential therapeutic biomarkers for FLU, which may significantly contribute for the optimization of the treatment of depression with FLU in the future.