Medication adherence affects treatment modifications in patients with Type 2 diabetes

Background: Low rates of treatment modification in patients with insufficiently controlled risk factors are common in type 2 diabetes. Although adherence problems are often mentioned in surveys as a reason for not intensifying treatment, observational studies have shown inconclusive results. Objective: To assess how medication adherence affects treatment modifications for hypertension and hyperglycemia in patients with type 2 diabetes. Methods: This was a cohort study of 11,268 primary care patients with type 2 diabetes in the Netherlands. Inclusion criteria were diagnosis before 2007, >= 1 prescription to antihypertensive or glucose-regulating medication in the preceding 6 months, and a systolic blood pressure level >= 140 mm Hg or glycosylated hemoglobin >= 7% in 2007. Patients on maximal treatment were excluded. Treatment modifications as observed from prescriptions were classified as none, dose increase, dose decrease, class switch, class addition, or class discontinuation. Refill adherence was assessed as medication possession ratio or length of last gap between refills. We performed multilevel multinomial regression analysis to test for associations. Results: We included 4980 diabetic patients with elevated blood pressure and 2945 diabetic patients with elevated glycosylated hemoglobin levels. Patients with lower adherence for antihypertensive drugs were more likely to have those medications discontinued (odds ratio [OR] for every 10% lower medication possession ratio =1.22; 95% CI, 1.11-1.33) or the dose decreased (OR = 1.14; CI 1.01-1.28). For glucose-regulating medication, dose increases (OR = 0.92; 95% CI, 0.85-0.98) and medication additions (OR = 0.90; 95% CI, 0.82-0.99) were less likely in patients with lower adherence levels. Conclusions: Low adherence inhibits the intensification of glucose-regulating but not antihypertensive medication in type 2 diabetic patients with insufficiently controlled risk factors in the Netherlands. Adherence problems may lead to diminished or even discontinued antihypertensive treatment. (Clin Ther. 2011;33:121-134) (c) 2011 Elsevier HS Journals, Inc