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Abstract and Introduction
Abstract
objective: To evaluate barriers to and strategies for medication adherence and predictors of adherence and the primary outcome in the Diabetes Prevention Program (DPP).
Research Design and Methods: Within a randomized, controlled primary prevention study for type 2 diabetes, we collected data on study medication adherence, its predictors, and health outcomes in 27 clinical centers across mainland U.S. and Hawaii. Medication arm participants included 2,155 adults with impaired glucose tolerance randomly assigned to either metformin or matched placebo treatment arms. Structured interviews were used to promote medication adherence and to collect data regarding adherence. Adherence was measured by pill count. The primary DPP outcome of type 2 diabetes was assessed by fasting plasma glucose and oral glucose tolerance test.
Results: Older age-groups were more adherent than the youngest group (P = 0.01) in the metformin group. The most frequently reported barrier to adherence was "forgetting" (22%). Women reported more adverse effects of metformin (15 vs. 10%, P = 0.002) in the metformin group. Odds of nonadherence increased as participants reported more than one barrier (odds ratio 19.1, P < 0.001). Odds of adherence increased as participants reported multiple strategies to take medication (2.69, P < 0.0001). There was a 38.2% risk reduction for developing diabetes for those adherent to metformin compared with those adherent to placebo (P < 0.0003).
Conclusions: DPP medication adherence results are unique in primary prevention for a chronic disease in a large multiethnic sample. Our finding that adherence was associated with risk reduction for diabetes supports the development of brief interventions in clinical settings where medication adherence is a challenge.
Introduction
The Diabetes Prevention Program (DPP) was a multicenter study to evaluate the effect of two interventions, an intensive lifestyle intervention or metformin compared with a placebo medication, on delaying or preventing type 2 diabetes in high-risk individuals with impaired glucose tolerance. Results demonstrated that among 3,234 participants with impaired glucose tolerance who were followed for an average of 3.2 years, the intensive lifestyle intervention reduced the incidence of diabetes by 55% and the metformin intervention reduced the incidence by 30% compared with the placebo group.
Patient adherence to medical recommendations is a problem that has been studied over decades. Data from medication adherence studies indicate that between 20 and 60% of patients fail to follow prescriptions. Since preventive medications do not provide the positive reinforcement of symptom control or relief, compared with effective therapeutic medications, adherence may be even more of a challenge, especially in primary prevention. Previous studies have reported patient characteristics, such as age, sex, ethnicity, socioeconomic status, levels of social support, anxiety or depression, and past history of adherence to the medications, as moderators or predictors of medication adherence. Complexity of the therapeutic regimen and the characteristics of health care systems and providers are also important variables in understanding medication adherence.
The DPP cohort is a unique population for evaluating preventive medication adherence because of the large sample size, diversity of age and ethnic/racial groups, and the prospective design of the study. This report focuses on medication adherence and its predictors and health outcomes in the metformin and placebo groups during the DPP. In addition, it reports barriers to adherence and the relative effectiveness of strategies to improve medication adherence.
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