Non-adherence to antidepressant medications is a major barrier to achieving treatment response and remission in clinical practice. Medication possession ratio (MPR) has been used to reflect treatment adherence of patients with chronic conditions including depression. An MRP =/> 80% correlates with high compliance. Systematic reviews of interventions to improve antidepressant medication adherence found that education interventions failed to demonstrate clear benefit on adherence; however, proactive care and collaborative care management (CCM) were associated with significant degree of adherence and improved clinical outcomes (1, 2). We looked into MPR measured from our institution's administrative pharmacy data among patients with depression seen at Primary Care Internal Medicine and enrolled in CCM from March 2008 until July 2012; we also determined predictors of non-adherence. Data was analyzed on 515 patients who gave research consent.

Yearly mean MPR was calculated at 6 month intervals beginning December 2010 until July 2012. Rate of yearly MPR =/> 80% ranged from 27% to 42% but remained consistent beyond the timeframe of CCM enrollment. Race, presence of co-morbid hypertension and hyperlipidemia were associated with significantly decreased medication adherence (MPR<80%) in univariate analysis but were not independent predictors of nonadherence in multivariate analysis.

In conclusion, approximately one third of patients with depression enrolled in CCM exhibited high medication adherence reflected by mean MRP =/>80%. While CCM has resulted in 46% remission rate at 12 months in this patient group, medication adherence appeared to be lower which implied that features intrinsic to CCM may account mostly for depression treatment effectiveness.