Usage of medications with high potential to interact with warfarin among atrial fibrillation residents in long-term care facilities

OBJECTIVES: The rate of potential warfarin drug-drug interactions among long-term care (LTC) residents with atrial fibrillation (AFib) is evaluated. RESEARCH DESIGN AND METHODS: LTC residents from two databases, the National Nursing Home Survey (NNHS) 2004 and the AnalytiCare™ multistate database, with an AFib diagnosis (ICD9 = 427.3x) were studied. Concurrent usage was tabulated for 10 agents/pharmacotherapeutic classes (simple-class screen) and for 96 individual agents (single-agent screen) with strong evidence for warfarin-interaction. RESULTS: Warfarin use was recorded in 502 NNHS and 1,674 AnalytiCare residents with AFib. Using the simple-class screen, ≥ 1 of the 10 classes/agents were prescribed concurrently in 59% (CI: 54.0 - 63.6%) of warfarin users in NNHS and 85% (CI: 82.9 - 86.3%) in AnalytiCare. Using the more comprehensive single-agent screen, usage of any interacting agent was higher in both databases: 87% (CI: 83.9 - 90.3%) in NNHS and 94% (CI: 93.0 - 95.3%) in AnalytiCare. Among 873 interacting agents dispensed to residents while continuously using warfarin (AnalytiCare database), 360 (41%) were changed (added or withdrawn), while 513 (59%) were maintained over two consecutive 45-day periods. CONCLUSIONS: Concurrent use of agents with a high potential for interaction occurs among most LTC residents who are receiving warfarin. Large proportions of interacting agents appear to be added or withdrawn during continuous warfarin therapy and thus have implications for anticoagulation control.