Impact of adherence to antidepressants on healthcare outcomes and costs among patients with type 2 diabetes and comorbid major depressive disorder

Objective: To evaluate the association between adherence to antidepressants and an effect on clinical outcomes and healthcare costs in patients with major depressive disorder (MDD) and comorbid type 2 diabetes (T2D). Methods: This retrospective study used MarketScan claims data from January 2012 to March 2014. Study entry was the first claim for an antidepressant and a diagnosis code for MDD and T2D in the prior 6 months. Adherence and persistence with antidepressant therapy in the first 180 days were defined as medication possession ratio (MPR) >= 80% and length of therapy (LOT), with no treatment gap of >15 days, respectively. T2D control (HbA1c <7%), oral diabetes medication adherence, and healthcare costs were measured in the 12 month post-index period. The impact of antidepressant adherence and persistence on outcomes was assessed using multivariable analyses. Results: Among the 1361 patients included, the mean age was 59 years and 55% were women. About one-third of the patients were adherent (35.9%, mean MPR = 40%), persistent (32.0%, average LOT = 100 days), and adherent/persistent (31.2%) on antidepressants. Being adherent, persistent, or adherent/persistent to antidepressants was associated with a two-fold improvement in adherence to oral diabetes medications. Of those with HbA1c data (n = 121), adherence or adherence/persistence to antidepressants was associated with patients being five times more likely to have T2D control (odds ratio [OR]: 4.95; 95% confidence interval [CI]: 1.39, 17.59, p = .0134). Comparison between antidepressant-persistent and non-persistent patients was not significant. Mean difference in adjusted all-cause annual costs showed lower costs among antidepressant-adherent and adherent/persistent patients (adherent: -$350, 95% CI: -$462, -$247; adherent/persistent: -$1165; 95% CI: -$1280, -$1060). Conclusions: Patients with better antidepressant adherence and adherence/persistence demonstrated better HbA1c control, with lower all-cause total and medical costs. Adherence, persistence, or adherence/persistence to antidepressants was associated with improved adherence to oral diabetes medications.