Association of Medication Adherence With HbA1c Control Among American Indian Adults With Type 2 Diabetes Using Tribal Health Services

Abstract

OBJECTIVE To examine HbA1c levels and adherence to oral glucose-lowering medications and their association with future HbA1c levels among American Indian adults with type 2 diabetes (T2D) receiving medications at no cost from a tribal health care system. RESEARCH DESIGN AND METHODS Tribal citizens with T2D who used Choctaw Nation Health Services Authority (CNHSA) and Pharmacies and had HbA1c data during 2017–2018 were included in this study. Medication adherence (proportion of days covered [PDC] ≥0.80) was calculated using 2017 CNHSA electronic health record data. RESULTS Of the 74,000 tribal citizens living on tribal lands, 4,560 were eligible; 32% had HbA1c at or below target (≤7%), 36% were above target (>7 to ≤9%), and 32% were uncontrolled (>9%) in 2017. The percentage of patients with PDC ≥0.80 was 66% for those using biguanides, 72% for sulfonylureas, 75% for dipeptidyl peptidase 4 inhibitors, and 83% for sodium–glucose cotransporter 2 inhibitors. The proportion of patients with HbA1c at or below target increased slightly from 32% in 2017 to 42% in 2018. Higher average PDC in 2017 was associated with lower HbA1c levels in 2018 (β = −1.143; P < 0.001). CONCLUSIONS Medication adherence was higher than that found in previous studies using self-report methods in American Indian populations, although a smaller proportion of patients had HbA1c at or below target relative to U.S. adults with T2D. Medication adherence was associated with improved HbA1c levels for most oral glucose-lowering medication classes. Future studies of American Indians should use both longitudinal prescription data from both electronic health records and pharmacy refills.