Prevalence of potentially hazardous drug interactions amongst Australian veterans.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT * Up to 21% of adverse drug event related hospital admissions are due to drug interactions. Clinical significance of drug interactions varies. * Studies which only identified drug interactions of potentially major clinical significance found lower prevalence, of between 2 and 16%. * Prevalence of drug interactions defined 'potentially hazardous' has had limited study, with no publications identified for the Australian population. WHAT THIS STUDY ADDS * In the study population of 287 074, 1.5% of subjects were dispensed potentially hazardous interacting drug pairs. * However, limited to populations on specific medicines, it was found that for patients dispensed verapamil, methotrexate, amiodarone, lithium, warfarin, cyclosporin and itraconazole, potentially hazardous interactions occurred at a rate greater than 5%. * These patients should be the focus of medication review programmes to avoid potentially serious adverse drug events. BACKGROUND Up to 21% of adverse drug event-related hospital admissions are due to drug interactions. Clinical significance of drug interactions varies, and drug interactions defined 'potentially hazardous' are more likely to contribute to morbidity and mortality. AIM The aim of this study was to assess the prevalence of potentially hazardous drug interactions in an elderly Australian veteran population. METHODS This study assessed the prevalence of potentially hazardous drug interactions, where hazardous was defined in three or more international drug interaction references, using Repatriation Pharmaceutical Benefits Scheme pharmacy claims data. Analysis was limited to patients who received regular concurrent dispensings of potentially hazardous interacting medicines. RESULTS Of the 287 074 subjects included in the study, 1.5% were dispensed potentially hazardous interacting drug pairs. For patients dispensed cyclosporin, concomitant use of a statin was common (47%); as was statin use with those dispensed itraconazole (31%). Of those dispensed methotrexate, 24% also received a non-steroidal anti-inflammatory drug; of those on lithium, 18% also received an ACE inhibitor or angiotensin 2 receptor blocker; of those on warfarin, 7.2% and 5.9% were co-dispensed an non-steroidal anti-inflammatory drugs or antiplatelets respectively; for those on verapamil, 5.3% were co-dispensed a beta-blocker, while for those on amiodarone 6.2% were co-dispensed digoxin. CONCLUSIONS Overall prevalence of potentially serious drug interactions appears to be low in the Australian veteran population. However, patients taking cyclosporine, itraconazole, methotrexate, lithium, warfarin, verapamil and amiodarone appear to be most at risk and their medicine use should be regularly reviewed to prevent potentially hazardous drug interactions.