Pharmacogenomic-Guided Prescribing for Treatment-Resistant Mental Health Conditions in Australian Primary Care: A Single-GP Practice Retrospective Observation of 29 Patients.

Treatment-resistant mental health conditions are common in primary care and challenging for clinicians. Trial-and-error prescribing can prolong morbidity and increase adverse drug reactions (ADRs). Pharmacogenomic (PGx) testing enables individualised prescribing by identifying gene-drug interactions affecting psychotropic response. Thirty adults with treatment-resistant mental health conditions underwent PGx testing using a commercial panel (one lost to follow-up [n = 29]). Patients received PGx-guided treatment (n = 8) or standard care (n = 21). Phenotypes were assigned per CPIC and DPWG guidelines, with prescribing guided by clinical experience where guidelines were unavailable. Medication histories were reviewed for gene-drug concordance, ADRs, and treatment failures. Clinical improvement at eight weeks was defined as "marked" or "moderate" improvement and/or ADR resolution. Actionable genotypes were common, particularly CYP2D6 (27.5% poor/intermediate drug metabolising phenotype) and CYP2C19 (37.9%). Guideline-actionable gene-drug interactions occurred in 37% of patients, and eleven patients possessed actionable phenotype at multiple loci. Gene-drug interactions were identified in nine patients and guidance was fully implemented in six. Clinical benefit at 8 weeks was achieved in 6/8 patients with genotype-guided changes versus 8/21 receiving standard care. PGx-guided prescribing may support improved antidepressant response and tolerability while reducing trial-and-error prescribing for treatment-resistant patients in primary care.