Estimating the potential impact of implementing pre-emptive pharmacogenetic testing in primary care across the UK

Aims: Pharmacogenetics (PGx) in the UK is currently implemented in secondary care for a small group of high‐risk medicines. However, most prescribing takes place in primary care, with a large group of medicines influenced by commonly occurring genetic variations. The goal of this study is to quantitatively estimate the volumes of medicines impacted by implementation of a population‐level, pre‐emptive pharmacogenetic screening programme for nine genes related to medicines frequently dispensed in primary care in 2019. Methods: A large community pharmacy database was analysed to estimate the national incidence of first prescriptions for 56 PGx drugs used in the UK for the period 1 January–31 December 2019. These estimated prescription volumes were combined with phenotype frequency data to estimate the occurrence of actionable drug–gene interactions (DGI) in daily practice in community pharmacies. Results: In between 19.1 and 21.1% (n = 5 233 353–5 780 595) of all new prescriptions for 56 drugs (n = 27 411 288 new prescriptions/year), an actionable drug–gene interaction (DGI) was present according to the guidelines of the Dutch Pharmacogenetics Working Group and/or the Clinical Pharmacogenetics Implementation Consortium. In these cases, the DGI would result in either increased monitoring, guarding against a maximum ceiling dose or an optional or immediate drug/dose change. An immediate dose adjustment or change in drug regimen accounted for 8.6–9.1% (n = 2 354 058–2 500 283) of these prescriptions. Conclusions: Actionable drug–gene interactions frequently occur in UK primary care, with a large opportunity to optimise prescribing