Implementation of a CYP2C19 testing service to guide antiplatelet therapy

This is a mixed methods research study consisting of a CYP2c19 genetic testing service (Phase 1) and qualitative methods (Phase 2). Phase 1 is a non-randomised prospective clinical study that implements a CYp2C19 genetic testing service in patients that have undergone a percutaneous coronary intervention, to inform antiplatelet therapy. The intervention is a pharmacogenomic test using a blood sample. Approximate turnaround time between the pharmacogenomic test and the results is five days. The results of the pharmacogenomic test will be reviewed by the participants treating cardiologist who will make prescribing considerations (e.g. ticagrelor or prasugrel instead of clopidogrel if the participant has a CYP2C19 loss-of-function genotype (defined as poor or intermediate metaboliser)). The treating cardiologist will communicate (via letter) the results and recommendations to the participants general practitioner and referring cardiologist. Practitioners reserve the right not to action antiplatelet therapy changes based on their clinical judgement. Participants will be contacted to determine their current antiplatelet therapy. This will be compared with their CYP2C19 genotype results to evaluate the proportion of new or revised prescriptions based on the CYP2C19 genotype result.