Choice of oral anticoagulant prescribed by general practices in Wales: Application of Dirichlet regression and linked data

AIMS: There has been sustained growth in the prescribing of direct oral anticoagulants (OACs) in primary care in the UK. Given the different indications, properties and prices of OACs, variation between prescribers is expected; however, a high level of variation may be evidence of inappropriate or suboptimal prescribing. This study examined the variation in the relative use of OACs in primary care in Wales. METHODS: Data on total defined daily doses of all community-dispensed OACs in 2019 were linked at the GP practice level with disease registers, patient demographic data and GP and patient numbers. The relative use of each OAC, as a fraction of all OACs prescribed, was analysed using Dirichlet regression to quantify the association between prescribing patterns and practice and area-level characteristics. RESULTS: Across 417 GP practices, the mean (range) in the relative prescribing of warfarin was 37% (6%-64%), apixaban was 32% (2%-65%), rivaroxaban 23% (0%-66%), dabigatran 3% (0%-23%) and edoxaban 6% (0%-59%). Statistical modelling provided strong evidence that prescribing patterns are associated with a GP practice's health board and also their nearest major hospital. Compared to the null model, a model including health board resulted in a 15% fall in Akaike information criterion, increasing to 20% with the addition of nearest major hospital and 27% including further covariates. CONCLUSION: Systematic variation in OAC prescribing, by health board and based on nearest hospital, indicates that factors other than patient clinical characteristics and preferences may be influencing prescribing decisions.