Co-prescribing of Warfarin with Statins and Proton Pump Inhibitors in Elderly Australians

Background: Comorbidity is common in individuals with atrial fibrillation (AF). The predominant treatment for AF is warfarin and medicine interactions with warfarin represent a challenge for optimising treatment of AF in older people with comorbidities. Statins and Proton Pump Inhibitors are commonly prescribed therapies and in both classes, there are medicines with greater or lesser potential to interact with warfarin. Objective: The aim of this study was to examine use of antithrombotic treatment in elderly Australians, and the extent of concurrent use of interacting statins and proton pump inhibitors (PPIs) with warfarin. Methods: A retrospective cohort study was conducted using data from the Australian Government Department of Veterans’ Affairs. The cohort included all patients who had at least one hospitalisation with a primary diagnosis for AF between 2007 and 2011. Individuals contributed person-months from the date of first AF hospitalisation to death or end of study (December 2011). Monthly utilisation of antithrombotics was assessed. A sub-cohort of warfarin users was defined as those with AF who received warfarin as monotherapy and the proportions of those co-dispensed statins or PPIs were established. Results: Around 70% of patients with AF were receiving antithrombotic treatment, with 35% dispensed warfarin, 17% aspirin, and 7% clopidogrel as monotherapy. In December 2011, 54% of patients with AF on warfarin monotherapy were co-dispensed a statin, with the statins with potential for interaction dispensed at highest rates; atorvastatin followed by simvastatin and rosuvastatin. At study end, 43% of the warfarin cohort were also dispensed PPIs, with one-third using esomeprazole, followed by pantoprazole, both of which have the potential to interact with warfarin. Conclusion: 30% of patients with AF were not receiving antithrombotic treatment. In those receiving an antithrombotic agent, warfarin was the most commonly dispensed (35%). The most common statin and PPI coprescribed with warfarin were agents with the potential to interact with warfarin, despite alternative agents being available. Raising awareness of the safer alternative for people with comorbidities may improve warfarin management.