Chronic medication adherence: its association with health care costs.

Abstract

Effective treatment for high-prevalence chronic diseases requires medication adherence. Improved medication adherence increases medication utilization, which leads to higher pharmacy costs. However, higher adherence may reduce medical services use that result in decrease in overall health care costs despite the increase in pharmacy costs. The objective of this study was to examine the impact of medical adherence on health care costs. The secondary objective of this study was to assess the independent effect of consumer directed health plans (CDHPs) on health care costs. The study samples were three independent cohorts of individuals with the separate conditions of diabetes, hypertension and hypercholesterolemia, identified from a pharmacy benefits management company between January 1, 2007 and December 31, 2009. Medication adherence was measured using Proportion of Days Covered (PDC) endorsed by Pharmacy Quality Assurance (PQA). Health care costs were measured at two levels: all-cause and condition-specific. At each level, pharmacy, medical and total health care costs were calculated. The generalized linear model with a gamma log link was used to fit six statistical models for each disease cohort. Control variables included patients’ demographics, socioeconomic information, health status, health services utilization. There were 22,012 individuals in the diabetes cohort, 64,600 in the hypertension cohort and 59,003 in the hypercholesterolemia cohort. At all-cause level, increased PDC was significant associated with decreased medical costs across the three cohorts (p<0.05). At condition-specific level, increased PDC was significant associated with decreased medical costs in the hypertension and hypercholesterolemia cohorts (p<0.001), but with increased medical cost in the diabetes cohort (p<0.001). Due to the significant increase in pharmacy costs associated with higher PDC (p<0.001), total health care costs were increased (p<0.001) both at all-cause and condition-specific levels in each cohorts. Enrollment in CDHPs was generally associated with decreased medical, pharmacy, and total health care costs at all-cause and condition-specific levels across the three cohorts. As adherence increases, the savings in medical costs are not able to offset the increase in pharmacy costs. Therefore, measures that aim to reduce pharmacy cost while preserving or improving adherence are needed.