Adherence to antidepressants and healthcare resource utilization and costs among medicare advantage beneficiaries with Parkinson’s disease and depression

Depression is the most common comorbid psychiatric disorder in patients with Parkinson’s disease (PD) and imposes a significant negative impact on PD. Studies have shown that antidepressants (ADs) may both treat depression and ameliorate its negative effects on PD. However, little has been reported regarding how improved adherence to antidepressants affects the outcomes among PD patients with depression. The purpose of this study was to examine antidepressant use patterns (adherence, persistence, switching, and combination therapy) and evaluate the associated healthcare utilization and costs in PD patients with comorbid depression. A retrospective cohort analysis using claims data from the Humana healthcare insurance plan (2007-2010) was conducted. Medicare Advantage with Prescription Drug (MAPD) Plan insured patients with ADs and a diagnosis of both depression and PD were identified and followed for one year. Healthcare resource utilization and costs were compared between adherent and non-adherent AD users while adjusting for demographic and clinical covariates. Adherence was defined as having at least 80 percent of AD coverage for the year, using proportion of days covered (PDC) calculations. A total of 856 PD patients initiating AD treatment were included. Less than half (N= 355 (41.5%) were considered adherent. The mean PDC (±SD) for antidepressants was 0.63 (± 0.31). The mean persistence (using a 30-day gap period) for antidepressants was 194 days. Having a regimen modification, (11% of patients had switching or combination therapy) was associated with a greater likelihood of being adherent (odds ratio = 2.97, 95% CI = [1.88, 4.68], p < 0.001) and a lower likelihood of discontinuation (hazard ratio = 0.63, 95% CI = [0.47, 0.84], p = 0.0016). After adjusting for covariates, adherent AD users had fewer all-cause and PD-related inpatient visits (all p < 0.05). Adherent AD users also had lower all-cause nursing facility, inpatient, emergency room (ER), and total costs (all p < 0.05) than non-adherent AD users. However, the results were no longer significant when assessing PD-related costs. In conclusion, regimen modification (switching, or combination therapy) to antidepressants was associated with better adherence and persistence in depressed PD patients. Adherent AD users had some lower healthcare utilization and costs than non-adherent AD users among depressed PD patients.