Multiple Pharmacy Use, Medication Adherence in Older Adults
Multiple Pharmacy Use, Medication Adherence in Older Adults
Table 2 displays sample characteristics overall and stratified according to pharmacy use patterns; 38.1% of the sample used multiple pharmacies, and 80.3% of those using multiple pharmacies (n = 352,964) used multiple pharmacies concurrently. Overall health status appeared to be the worst for the group filling at multiple pharmacies concurrently. Concurrent multiple pharmacy users obtained more unique medications (11.0 vs 8.1, P < .001), had a greater prevalence of all chronic conditions assessed, had more prescribers (4.5 vs 3.1, P < .001), and were more likely to use a mail order pharmacy as their primary pharmacy (15.0% vs 1.0%; P < .001) than single pharmacy users (Table 2). Those filling at multiple pharmacies sequentially also had greater use of mail order pharmacy as the primary pharmacy (7.1% vs 1.0%; P < .001) than those filling at a single pharmacy. After multiple propensity score weighting and adjustment, most of the initial differences between the pharmacy use groups were insignificant, and the remaining significant differences were reduced substantially in magnitude (Table 3).
Beneficiaries filling at multiple pharmacies concurrently used significantly more pharmacies throughout the year than those filling at multiple pharmacies sequentially (2.65 vs 2.19, P < .001), and filled a smaller proportion of the medications at their primary pharmacy (0.80 vs 0.85, P < .001).
Overall, a range of older adults were found to be non-adherent to the chronic medication classes assessed (26.1% taking calcium channel blockers to 41.5% taking thiazolidinediones; data not shown). Those using multiple pharmacies (concurrently and sequentially) consistently had a higher unadjusted likelihood of nonadherence (Figure 1). The same patterns held after adjusting for various sociodemographic, health status, and access-to-care factors using propensity score analysis (Table 4). For example, the adjusted predicted probability of single pharmacy users being nonadherent to beta-blockers was 29.8%, compared with 32.0% of individuals using multiple pharmacies concurrently (adjusted odds ratio (AOR) = 1.11, 95% CI = 1.09–1.13) and 34.1% of individuals using multiple pharmacies sequentially (AOR = 1.22, 95% CI = 1.18–1.26) (Table 3).
(Enlarge Image)
Figure 1.
Unadjusted rates of medication nonadherence for 2009 study cohort (n = 926,956). * P < .05 vs single pharmacy use group. CCB= Calcium Channel blocker; DPP= Dipeptidyl Peptidase; RASA= Renin Angiotensin System Antagonist.
Overall, 4.2% (n = 38,953) of participants were found to have at least one potential DDI (data not shown). Those using multiple pharmacies concurrently had a greater adjusted likelihood of a potential DDI (3.6%) than single pharmacy users (3.2%) (AOR = 1.11, 95% CI = 1.08–1.15). Conversely, the adjusted predicted probability of a potential DDI was lower in sequential multiple pharmacy users (2.8%) than in single pharmacy users (3.2%) (AOR = 0.85, 95% CI = 0.81–0.91) (Table 5). For those who used more than one pharmacy and had at least one potential DDI, 38.4% of the interactions involved medications filled at different pharmacies. Warfarin was involved in eight of the 10 most frequent DDIs. Post hoc analysis showed that 42.4% of beneficiaries using warfarin were using multiple pharmacies.
Results
Sample Characteristics
Table 2 displays sample characteristics overall and stratified according to pharmacy use patterns; 38.1% of the sample used multiple pharmacies, and 80.3% of those using multiple pharmacies (n = 352,964) used multiple pharmacies concurrently. Overall health status appeared to be the worst for the group filling at multiple pharmacies concurrently. Concurrent multiple pharmacy users obtained more unique medications (11.0 vs 8.1, P < .001), had a greater prevalence of all chronic conditions assessed, had more prescribers (4.5 vs 3.1, P < .001), and were more likely to use a mail order pharmacy as their primary pharmacy (15.0% vs 1.0%; P < .001) than single pharmacy users (Table 2). Those filling at multiple pharmacies sequentially also had greater use of mail order pharmacy as the primary pharmacy (7.1% vs 1.0%; P < .001) than those filling at a single pharmacy. After multiple propensity score weighting and adjustment, most of the initial differences between the pharmacy use groups were insignificant, and the remaining significant differences were reduced substantially in magnitude (Table 3).
Multiple Pharmacy Use
Beneficiaries filling at multiple pharmacies concurrently used significantly more pharmacies throughout the year than those filling at multiple pharmacies sequentially (2.65 vs 2.19, P < .001), and filled a smaller proportion of the medications at their primary pharmacy (0.80 vs 0.85, P < .001).
Medication Nonadherence
Overall, a range of older adults were found to be non-adherent to the chronic medication classes assessed (26.1% taking calcium channel blockers to 41.5% taking thiazolidinediones; data not shown). Those using multiple pharmacies (concurrently and sequentially) consistently had a higher unadjusted likelihood of nonadherence (Figure 1). The same patterns held after adjusting for various sociodemographic, health status, and access-to-care factors using propensity score analysis (Table 4). For example, the adjusted predicted probability of single pharmacy users being nonadherent to beta-blockers was 29.8%, compared with 32.0% of individuals using multiple pharmacies concurrently (adjusted odds ratio (AOR) = 1.11, 95% CI = 1.09–1.13) and 34.1% of individuals using multiple pharmacies sequentially (AOR = 1.22, 95% CI = 1.18–1.26) (Table 3).
(Enlarge Image)
Figure 1.
Unadjusted rates of medication nonadherence for 2009 study cohort (n = 926,956). * P < .05 vs single pharmacy use group. CCB= Calcium Channel blocker; DPP= Dipeptidyl Peptidase; RASA= Renin Angiotensin System Antagonist.
Potential Drug–Drug Interactions
Overall, 4.2% (n = 38,953) of participants were found to have at least one potential DDI (data not shown). Those using multiple pharmacies concurrently had a greater adjusted likelihood of a potential DDI (3.6%) than single pharmacy users (3.2%) (AOR = 1.11, 95% CI = 1.08–1.15). Conversely, the adjusted predicted probability of a potential DDI was lower in sequential multiple pharmacy users (2.8%) than in single pharmacy users (3.2%) (AOR = 0.85, 95% CI = 0.81–0.91) (Table 5). For those who used more than one pharmacy and had at least one potential DDI, 38.4% of the interactions involved medications filled at different pharmacies. Warfarin was involved in eight of the 10 most frequent DDIs. Post hoc analysis showed that 42.4% of beneficiaries using warfarin were using multiple pharmacies.
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