Effect of Multiple Pharmacy Use on Medication Adherence and Drug–Drug Interactions in Older Adults with Medicare Part D

Abstract

Objective To assess the association between multiple pharmacy use and medication adherence and potential drug-drug interactions (DDIs) among older adults. Design, Setting, and Participants Cross-sectional propensity score-weighted analysis of 2009 claims data from a nationally representative sample of 926,956 Medicare Part D beneficiaries aged >65 continuously enrolled in fee-for-service Medicare and Part D that year, and filled >1 prescription at a community/retail or mail order pharmacy. Multiple pharmacy use was defined as concurrent (overlapping time periods) or sequential use (non-overlapping time periods) of >2 pharmacies in the year. Measurements Medication adherence was calculated using a proportion of days covered ≥0.80 for eight therapeutic categories (β-blockers, renin angiotensin system antagonists, calcium channel blockers, statins, sulfonylureas, biguanides [i.e., metformin], thiazolidinediones, and dipeptidyl peptidase-IV inhibitors). Potential DDIs arising from use of certain drugs across a broad set of classes were defined as the concurrent filling of two interacting drugs. Results Overall, 38.1% of the sample used multiple pharmacies. Those using multiple pharmacies (both concurrently and sequentially) consistently had higher adjusted odds of non-adherence (ranging from 1.10 to 1.31, p<0.001) across all chronic medication classes assessed after controlling for socio-demographic, health status and access to care factors, compared to single pharmacy users. The adjusted predicted probability of exposure to a DDI was also slightly higher for those using multiple pharmacies concurrently (3.6%) compared to single pharmacy users (3.2%, AOR 1.11, 95% CI 1.08–1.15) but lower in individuals using multiple pharmacies sequentially (2.8%, AOR 0.85, 95% CI 0.81–0.91). Conclusions Filling prescriptions at multiple pharmacies was associated with lower medication adherence across multiple chronic medications, and a small but statistically significant increase in DDIs among concurrent pharmacy users.

Patient characteristics associated with multiple pharmacy use in the U.S. population: Findings from the Medical Expenditure Panel Survey

“…The MPU prevalence seen in this study was comparable with the national prevalence reported in 2009 for both the general adult population and among older adults. 5,10 This suggests that the increasing MPU trend seen over the past decade may have abated somewhat between 2009 and 2011. 10 Pharmacists play an important role in ensuring safe and appropriate drug therapy for their patients; however, they need to be aware that Pharmacists and prescribers may encourage their patients to use one pharmacy whenever possible to improve patient safety and ensure continuity of care.…”

“…Identification and management of potentially harmful MPU patterns may in turn reduce undesirable outcomes affecting patient safety. [3][4][5][6][7][8][9] Limitations This study had several limitations. First, because much of the MEPS data are self-reported, they could be subject to recall bias (e.g., not remembering all pharmacies or the types of pharmacies used) and social desirability bias (e.g., perceptions that using multiple pharmacies is bad).…”

“…2,3,9 The use of multiple pharmacies is common, with 38.1% of older adults with Medicare Part D using multiple pharmacies in 2009. 5 It is also becoming increasingly prevalent on a national level, with the prevalence of MPU among adults 18 years and older increasing from 36.4% in 2003 to 43.2% in 2009, a relative increase of 18.7%. 10 Although several studies have identified potential associations between MPU and demographic characteristics, these findings have been inconsistent among the few studies that have been conducted.…”

“…It results in fragmented patient care, because an individual pharmacy's records may not contain medications dispensed at other pharmacies, which decreases the pharmacist's ability to monitor for drug interactions and provide appropriate patient consultation. [1][2][3][4] Of particular concern for prescribers, hospitals, and health plans, MPU has been linked to many undesirable outcomes affecting patient safety or quality of care, including inappropriate drug use and adverse drug reactions, 4-6 decreased patient adherence, 5,7,8 increased mortality, 3 and an increase in ambulatory care and hospital expenditures. 2,3,9 The use of multiple pharmacies is common, with 38.1% of older adults with Medicare Part D using multiple pharmacies in 2009.…”

Availability of prescription drugs for bipolar disorder at online pharmacies

“…In a national survey of 89,941 patients, 43.2% used multiple pharmacies, with 29.1% of these using 3 or more pharmacies (Look and Mott, 2013). An analysis of 926,956 Medicare Part D claims found that 38.1% of patients used multiple pharmacies, with 25% using them concurrently (Marcum et al, 2014).…”