Process evaluation of a pharmacogenomic informed antidepressant prescribing intervention delivered in primary care: findings from the PRESIDE (PhaRmacogEnomicS in Depression) trial

BACKGROUND: Major depressive disorder (MDD) impacts 300 million people globally, with most people being managed in primary care. Clinical response to antidepressant medications is highly variable. Pharmacogenomics (PGx) may improve prescribers' ability to match an antidepressant medication with patient phenotype, increasing the likelihood of a response. OBJECTIVES: This process evaluation aims to understand factors that impacted PGx intervention implementation in the PRESIDE Trial, conducted in general practices in Victoria, Australia. METHODS: Antidepressant prescribing data, evidence of intervention use and qualitative data from interviews with participants were included. Analysis and interpretation of the data were informed by the (UK) Medical Research Council's Framework for Developing and Evaluating Complex Interventions. RESULTS: While clinicians and patients supported PGx informed antidepressant prescribing, documented uptake of the intervention was low, as were antidepressant medication initiations or changes in line with the PGx report. Participants reported a lack of clarity regarding follow-up processes post PGx report return. The impact of COVID-19 during trial implementation included delays to intervention delivery. The provision of mental health care in primary care settings was also impacted. CONCLUSIONS: Future applications of PGx informed antidepressant prescribing would benefit from refined patient selection and ensuring PGx information is available when most useful.