Impact of medication adherence on renal function in comorbid patients with type 2 diabetes and depression: protocol for a cohort study

Background: Prevention, or slowing the progression, of diabetic nephropathy is one of the important goals in diabetes care. Although the impact of depression is a concern in patients with diabetes, it is unknown whether there is an association between adherence to hypoglycemic medication and the decline of renal function in comorbid patients with diabetes and depression. We will conduct a cohort study aimed at examining (1) depression as a predictor of renal function decline, and (2) how adherence to hypoglycemic medication relates to depression and renal function decline in patients with type 2 diabetes. Methods/Design: In this multicenter cohort study, 550 patients with type 2 diabetes aged 20 years and older will be recruited at 20 outpatient clinics in general medicine and psychiatry. We will measure depression (Patient Health Questionnaire), medication adherence (medication possession ratio, Morisky Medication Adherence Scale, and one-item hypoglycemic medication adherence scale), and renal function (urinary albumin-creatinine ratio and estimated glomerular filtration rate) at baseline and at the 12-month follow-up. The primary endpoint is decline of renal function at 12 months. The secondary endpoints include clinical variables, quality of life, and the attitude of professionals toward depression. We will perform multivariable linear regression analysis to evaluate the effects of medication adherence on the decline of renal function in comorbid patients with type 2 diabetes and depression. Discussion: To our knowledge, this will be the first study to examine how adherence to hypoglycemic medication relates to the decline of renal function in comorbid patients with type 2 diabetes and depression. The results of the study will have implications for practitioners of diabetes care, policy makers, and researchers for the prevention and treatment of diabetic nephropathy. Trial registration: UMIN000017513 (Registered on May 22, 2015)