Advances in Pharmacoepidemiology and Drug Safety

Abstract

A Comparison of Data Driven-based Measures of Adherence to Oral Hypoglycemic Agents in Medicaid Patients

Vivienne J Zhu, Wanzhu Tu, Marc B Rosenman and J Marc Overhage

Objective: Using observational clinical data from our local operational health information exchange, we evaluated different methods for measuring adherence to Oral Antihyperglycemic Agents (OHA) in patients with Type 2 diabetes. The primary objective is to compare different OHA adherence measures based on their associations with glycated hemoglobin A1c (HbA1c) levels. The secondary objective is to examine the relationship between patient demographic and clinical characteristics and HbA1c level. Methods: An observational sample of 831 Medicaid patients with Type 2 diabetes who had HbA1c test results recorded between January 1, 2001 and December 31, 2005 was identified in the Indiana Network of Patient Care (INPC). OHA adherence was measured by medication possession ratio (MPR), proportion of days covered (PDC), and the number of gaps (GAP) for 3, 6, and 12-month intervals prior to the HbA1c test date. The associations between these nine OHA adherence measures and HbA1c levels were examined and compared using mixed effects generalized linear models. Patient age, gender, race, duration of OHA treatment, number of concurrent OHAs, and OHA class were used to control the possible confounders in the analyses. Results: All three OHA adherence definitions showed consistent and significant association with HbA1c control. Unadjusted coefficients ranged -0.98 to -1.07 for PDC, -0.90 to -0.92 for MPR, and 0.25 to 0.19 for GAP. The 6-month PDC showed the strongest association with HbA1c levels in both unadjusted (-1.07, p<0.0001) and adjusted (-1.12, p<0.0001) models. Conclusion: Better OHA adherence is significantly associated with lower HbA1c level in Medicaid patients with Type 2 diabetes. The 6-month PDC is more highly correlated with the outcome than other OHA adherence measurements.