Pharmacogenomics of Antidepressant Response in Nigeria: CYP2D6 and CYP2C19 Polymorphisms and Clinical Outcomes

Inter-individual variability in antidepressant response is partly attributable to pharmacogenomic differences, yet cytochrome P450 polymorphism data from Nigerian populations are largely absent from clinical decision-support frameworks. This study examines the relationship between CYP2D6 and CYP2C19 genetic polymorphisms and antidepressant treatment outcomes in Nigerian patients with major depressive disorder. A prospective pharmacogenomic cohort will recruit 200 patients initiating antidepressant therapy at tertiary hospitals in Lagos, Abuja, and Kano. Blood samples will be collected at baseline for CYP2D6 and CYP2C19 genotyping using validated PCR-based methods. Patients will be phenotypically classified as poor, intermediate, extensive, or ultrarapid metabolizers. Depression outcomes (HDRS-17, PHQ-9) will be assessed at 2, 4, 8, and 12 weeks. Side effect burden will be documented using the Antidepressant Side Effect Checklist (ASEC). The primary outcome will be remission at 12 weeks, defined as HDRS-17 below 8. Ancestral stratification analyses will examine the influence of Hausa, Yoruba, and Igbo genetic backgrounds on CYP allele frequencies. This study constitutes a seminal pharmacogenomic investigation in Nigerian psychiatry, with direct translational implications for precision prescribing of antidepressants. Keywords: pharmacogenomics, CYP2D6, CYP2C19, antidepressant, Nigeria