Prevalence of nonadherence to multiple drug therapies among elderly medication users

Although medication nonadherence is recognized as an important barrier to effective disease treatment, relatively few studies have examined dimensions of nonadherence across multiple drug classes. Because the elderly are more likely than younger groups to be prescribed multiple medications, it is important to understand the prevalence of multiple drug nonadherence among older patients.

Using prescription claims from Pennsylvania's Pharmaceutical Assistance Contract for the Elderly (PACE) program, we examined refill patterns within 15 therapeutic classes. For cardholders who filled prescriptions in January 2001, refill frequencies over the subsequent 365 days were evaluated using the Medication Possession Ratio (MPR), which represents the proportion of days that medication was available within the cumulative prescribing interval. The sample included 67,801 community-dwelling elderly who remained non-hospitalized and enrolled in PACE throughout the one-year study. Multivariate logistic regression was used to examine factors associated with nonadherence.

Mean MPRs ranged from 0.860 for osteoporosis drugs to 0.958 for thyroid agents. Polypharmacy increased the likelihood of nonadherence. While 74% of persons taking two classes were fully adherent, only 59% of individuals using five classes had MPR>0.80 for all classes. Among elderly using four or more classes, African-Americans were more likely than whites to experience multiple nonadherence (OR=2.08, p<.0001). Users of diuretics (OR=1.26, p<.0001), osteoporosis drugs (OR=1.33, p<.0001), or overactive bladder treatments (OR=1.35, p=.0005) were also more likely to be nonadherent across multiple classes. These results highlight the importance of examining adherence within the context of all prescribed therapies. Additional results regarding specific nonadherence patterns will also be presented.