Does Medication Adherence Lead to Lower Healthcare Expenses for Patients With Diabetes? | Page 3
Published Online: August 13, 2013
Shou-Hsia Cheng, PhD; Chi-Chen Chen, PhD; and Chin-Hsiao Tseng, MD, PhD
In addition to these models, we conducted 3 sensitivity analyses to improve the robustness of this study. First, the diabetes and cardiovascular/cerebrovascular-related hospitalizations was originally based on Lau and Nau’s definition (2004).18 Because this definition only includes specific aspects of health conditions that are related to diabetes, we may have underestimated or overestimated the results of our study. Therefore, we examined the effects of medication adherence on healthcare outcomes and expenses based on more general definitions of diabetes-related conditions, including the definitions made by Sokol et al (2005)12 and Bethel et al (2007)1. Second, we used various MPR cut-off points to examine the stability of the association between MPR and healthcare outcomes as well as expenses. Finally, because the patients with diabetes were not randomly assigned to the medication-adherent group or nonadherent group, we used a PSM approach to minimize the selection bias and assigned patients with diabetes to the nonadherent group.17 We employed the caliper matching method (also known as the greedy algorithm) with 1-to-1 matching between the adherent and nonadherent groups based on the propensity score. A total of 7728 patients and 46,368 patient-years were included in the matched analysis. The analyses were performed using SAS version 9.1.3 (SAS Institute, Cary, North Carolina) and Stata 9.1 (Stata Corp, College Station, Texas).
Table 1 presents the baseline characteristics of the study subjects in the year being diagnosed with T2DM. In terms of basic characteristics, the mean age of subjects was 55.56 years. The average number of physician visits for any condition in the previous year was 23.77 and the rate of hospitalization in the previous year was 15.78%. Approximately 61.03% of the study sample had a DCSI score of 0, whereas 15.47% had a score of 2 or higher. In addition, 61.85% of the study sample had an average of more than 3 medications per prescription.
Table 2 presents the trends for interest variables. The average MPR slightly decreased from 75.21% in the first year after diagnosis of diabetes to 75.14% in the second year and then increased in the subsequent years to 88.87% in the last year of the study period. The proportion of patients who were considered to be adherent to oral antihyperglycemic medications (MPR >80%) increased during the study period. The rates of hospitalization for diabetes or cardiovascular/cerebrovascular conditions decreased from 9.04% in the first year after diagnosis of diabetes to 8.39% in the second year, respectively. These rates then increased in the subsequent years to 11.74% in the last year of the study period. The rate of ED visits for diabetes or cardiovascular/cerebrovascular conditions decreased from 6.25% in the first year to 5.40% in the second and third year and then increased steadily during the subsequent years. Additionally, the mean drug expenses for oral antihyperglycemic medications, the average expenses for diabetes or cardiovascular/cerebrovascular-related hospitalizations and ED visits, and total healthcare expenses increased during the study period.
Relationship Between Medication Adherence and Healthcare Outcomes
Table 3 presents the results of the GEE models concerning the relationship between medication adherence and healthcare outcomes. The first model examined the relationship between medication adherence and healthcare outcomes (Model 1). In the second model (Model 2), the interaction of medication adherence and the duration of diabetes was incorporated. In Model 1, patients with better medication adherence were less likely to be hospitalized for diabetes or cardiovascular/cerebrovascular-related conditions (odds ratio [OR] = 0.74, 95% confidence interval [CI] = 0.69-0.78). Similarly, patients with better medication adherence were less likely to have ED visits for diabetes or cardiovascular/ cerebrovascular-related conditions based on Model 1 (OR = 0.78, 95% CI = 0.73-0.84). In Model 2, the interaction term revealed that the duration of diabetes significantly moderated the relationship between medication adherence and hospitalization (OR = 0.86, 95% CI = 0.76-0.97) but did not moderate the relationship between medication adherence and ED visits (OR = 0.91, 95% CI = 0.79-1.05).
Relationship Between Medication Adherence and Healthcare Expenses
Results from the GEE models concerning the relationship between adherence and healthcare expenses are presented in Table 4. Patients in the adherent group had higher drug expenses for oral antihyperglycemic medications than did patients in the nonadherent group (β = 0.52, P <.001). However, patients in the adherent group had lower expenses for hospitalizations and ED visits for diabetes or cardiovascular/cerebrovascular-related conditions than did patients in the nonadherent group (β =–0.56, P <.001). The results indicated that adherence to oral antihyperglycemic medications was positively associated with total healthcare expenses for any condition (β = 0.09, P <.001). In addition, we found that the duration of diabetesmoderated the relationship between medication adherence and total healthcare expenses (β = –0.16, P <.001). These results indicated thatduring the 4 years following diagnosis, patients who had good medication adherence tended to have higher healthcare expenses than patients who had poor medication adherence. However, this relationship was attenuated at 5 years afterinitial diabetes diagnosis.
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