Open Access Research article

Racial differences in long-term adherence to oral antidiabetic drug therapy: a longitudinal cohort study

Connie M Trinacty1*, Alyce S Adams12, Stephen B Soumerai1, Fang Zhang1, James B Meigs3, John D Piette4 and Dennis Ross-Degnan1

Author Affiliations

1 Department of Ambulatory Care and Prevention, Harvard Medical School and Harvard Pilgrim Health Care, Boston, MA, USA

2 Division of Research, Kaiser Permanente Northern California, Oakland, CA, USA

3 General Medicine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA

4 VA Center for Clinical Management Research and Division of General Medicine, University of Michigan Health Care System, Ann Arbor, MI, USA

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BMC Health Services Research 2009, 9:24  doi:10.1186/1472-6963-9-24

Published: 7 February 2009



Adherence to oral antidiabetic medications is often suboptimal. Adherence differences may contribute to health disparities for black diabetes patients, including higher microvascular event rates, greater complication-related disability, and earlier mortality.


In this longitudinal retrospective cohort study, we used 10 years of patient-level claims and electronic medical record data (1/1/1992–12/31/2001) to assess differences in short- and long-term adherence to oral antidiabetic medication among 1906 newly diagnosed adults with diabetes (26% black, 74% white) in a managed care setting in which all members have prescription drug coverage. Four main outcome measures included: (1) time from diabetes diagnosis until first prescription of oral antidiabetic medication; (2) primary adherence (time from first prescription to prescription fill); (3) time until discontinuation of oral antidiabetic medication from first prescription; and (4) long-term adherence (amount dispensed versus amount prescribed) over a 24-month follow-up from first oral antidiabetic medication prescription.


Black patients were as likely as whites to initiate oral therapy and fill their first prescription, but experienced higher rates of medication discontinuation (HR: 1.8, 95% CI: 1.2, 2.7) and were less adherent over time. These black-white differences increased over the first six months of therapy but stabilized thereafter for patients who initiated on sulfonylureas. Significant black-white differences in adherence levels were constant throughout follow-up for patients initiated on metformin therapy.


Racial differences in adherence to oral antidiabetic drug therapy persist even with equal access to medication. Early and continued emphasis on adherence from initiation of therapy may reduce persistent racial differences in medication use and clinical outcomes.