Predictors of adherence to concomitant antihypertensive and lipid-lowering medications in older adults: a retrospective, cohort study.

Background: Many older individuals have concomitant hypertension and dyslipidaemia--two conditions that, together with age, increase the risk of adverse cardiovascular events. Adherence to antihypertensive (AH) and lipid-lowering (LL) therapy is therefore particularly important in older patients with concomitant hypertension and dyslipidaemia.

Objective: To determine patterns and predictors of adherence to concomitant AH and LL therapy among an older Medicare-eligible population.

Methods: Enrolees (n=4052) aged>or=65 years who initiated treatment with both AH and LL therapy within a 90-day period were studied in this retrospective cohort study conducted in a US managed care organization. Adherence to AH and LL medications was measured as the proportion of days covered by any AH and/or LL medication in each 3-month interval, from the start of concomitant therapy for up to 36 months (mean follow-up 19.5 months). In each interval, patients were considered 'adherent' to AH and LL therapy if they had filled prescriptions sufficient to cover>or=80% of days with both medication classes. A multivariable regression model evaluated potential predictors of adherence to concomitant therapy, including patient demographics, clinical characteristics and health services use patterns at baseline.

Results: The percentage of patients adherent to both AH and LL therapy declined rapidly, before stabilizing, with 40.5%, 32.7% and 32.9% adherent at 3, 6 and 12 months, respectively. At each timepoint, an additional 27.8-35.0% of patients were adherent to either AH or LL therapy, but not both. Adherence was on average greater to AH than LL therapy. After adjusting for age, sex and other potential predictors, patients were more likely to be adherent if AH/LL therapies were initiated closer together in time (adjusted odds ratio [AOR] 1.13 for 0-30 days vs 61-90 days, p=0.0563), had a history of cardiovascular disease (AOR 1.27, p=0.0004), took fewer additional medications (AOR 0.43 for six or more medications vs zero or one medication, p<0.0001) or had more outpatient physician visits in the prior year (AOR 1.26 for four to six visits vs zero to one visit, p<0.0027).

Conclusion: Adherence to concomitant AH and LL therapy among older adults is poor. Modifiable factors that may improve adherence in Medicare-eligible patients include initiating therapy concurrently and reducing patients' overall pill burden.