Impact of treatment adherence on the effectiveness and safety of oral anticoagulants in patients with atrial fibrillation: a retrospective cohort study

Aims The impact of adherence to oral anticoagulation has not been reported in terms of absolute risk, which would enhance patients' understanding and treatment adherence. Methods and results This retrospective cohort study analysed data from the National Health Insurance Database of Korea, from January 2010 to December 2018, on 84 227 patients with non-valvular atrial fibrillation (NVAF). The participants were analysed according to their overall adherence to oral anticoagulants (OACs) and further divided into four groups: non-vitamin K antagonist oral anticoagulant (NOAC) adherent, vitamin K antagonist (VKA) adherent, NOAC non-adherent, and VKA non-adherent. The incidence of ischaemic stroke, major bleeding, and death was compared between the four groups using risk difference, number needed to treat and number needed to harm. Among the participants, 50 178 were adherent to (OACs), while 34 049 were non-adherent. The incidence of major bleeding was higher in the adherent group (4.49%; 95% confidence interval, 4.11-4.85%) than in the non-adherent group (3.61%; 3.16-4.06%), and the incidence of ischaemic stroke was higher in the non-adherent group (7.68%; 7.08-8.33%) than in the adherent group (5.61%; 5.17-6.07%). In terms of risk difference, adherence to OACs increased the risk of major bleeding by 0.87% and decreased the risk of ischaemic stroke by 2.08%. This finding suggests that one additional major bleeding event occurred for every 115 adherent patients, and one additional ischaemic stroke event was prevented for every 48 adherent patients. Conclusion The benefits of OAC adherence in NVAF patients for ischaemic stroke prevention exceeding the risk of bleeding are shown more clearly in terms of absolute risk.