Examining the relationship between adherence and the number of cardiometabolic medications: Findings for patients with type 2 diabetes within a Tribal health care system.

Background: The literature is inconclusive regarding the association between adherence and the number of concurrent prescribed medications. Among patients with type 2 diabetes (T2D), low medication adherence is linked with inadequate glycemic management and increased diabetes-related complications. Adherence to glucose-lowering, lipid-lowering, and antihypertensive medications may be impacted by the number of cardiometabolic medications taken by adults with T2D, including American Indian adults.

Objective: To examine the association between medication adherence and the number of cardiometabolic medications among American Indian adults with T2D using Tribal health services, a health care system where all medical care and medications are provided free of charge.

Methods: We used 2019 medication dispensing data and patient data from the electronic health records of the Choctaw Nation Health Services Authority. Our sample included 6,774 American Indian adults aged 20 years and older, previously diagnosed with T2D, who received at least 1 cardiometabolic medication from a Choctaw Nation Health Services Authority pharmacy. We measured medication adherence as the proportion of days covered (PDC; possible range 0-1). Analysis of variance and chi-square tests were used to examine the association between the number of medications and patient characteristics. Multiple linear regression was used to estimate the association of adherence with patient characteristics.

Results: The sample mean age was 58.4 (SD = 13.2) years; 63.4% were aged 55 years or older; 47.8% were male; 49.6% were single; 36.9% had comorbidities. 30.9% were prescribed 2 or fewer medications, 43.1% were prescribed greater than 2 to 4 medications, and 26.0% were prescribed more than 4 medications. 71.7% had noninsulin glucose-lowering medications, 68% had lipid-lowering medication, and 90% had antihypertensive medications. Overall, 60.6% of the sample were adherent (PDC ≥ 0.80), including 49% of those with 2 or fewer medications, 62% of those with greater than 2 to 4 medications, and 72% with more than 4 medications. In a multiple regression model, adherence was positively associated with the number of medications (b = 0.026,  < 0.001), age 55 years or older (b = 0.062,  < 0.001), male sex (b = 0.009,  = 0.046), and presence of comorbidities (b = 0.033,  < 0.001) but negatively associated with being single (b = -0.034,  < 0.001) and insulin usage (b = -0.019,  < 0.001).

Conclusions: To our knowledge, this is the first study demonstrating the association between a higher number of cardiometabolic medications and better adherence in American Indian adults diagnosed with T2D whose medications were provided without cost to the patients. Medication cost is a well-known medication adherence barrier. Future studies should further examine factors associated with nonadherence in this population, such as younger age and fewer medications.