• Junling Wang, Xianchen Liu, and C Daniel Mullins.
• University of Tennessee College of Pharmacy, Memphis, TN 38163, USA. jwang26@uthsc.edu
• Curr Med Res Opin. 2011 Jul 1; 27 (7): 130313131303-13.

ObjectiveChronic pain is prevalent in patients with major depressive disorder (MDD). This study compared adherence and persistence rates among MDD patients with comorbid chronic pain-related diseases (CPD, including fibromyalgia, diabetes with neurological manifestations, osteoarthritis, low back pain, and headache) for three antidepressants: duloxetine, venlafaxine XR, and escitalopram.Research Design And MethodsA retrospective analysis was conducted of 15,523 adult MDD patients with CPD in the MarketScan Commercial Claims and Encounters Database who started on one of the study medications between 07/01/06 and 06/30/07. Patients were followed-up for 6 months. Adherence was reported using a medication possession ratio ≥0.8. Persistence was measured using persistence rates (proportions of patients who continuously refilled prescriptions during 6 months) and duration of therapy (number of days patients remained on the study medication before a prescription gap over 30 days). Multivariate logistic regression on adherence and persistence rates and linear regression on duration of therapy adjusting for patient and prescription characteristics were conducted.ResultsPatients on duloxetine had a higher adherence rate (46.03%) than those on venlafaxine XR (42.94%; p = 0.0033) or escitalopram (37.27%; p < 0.0001). Patients on duloxetine also had a higher persistence rate and longer duration of therapy (43.66%, 117.82 days) than did patients treated with venlafaxine XR (40.38%; p = 0.0017; 114.24 days; p = 0.009) or escitalopram (33.86%; p < 0.0001; 105.73 days; p < 0.0001). These differences were still significant after adjusting for patient and prescription characteristics (p < 0.05). Sensitivity analyses found similar patterns using an allowable gap for refill of 15 days.ConclusionsAmong commercially insured MDD patients with CPD, duloxetine-treated patients had higher adherence and persistence rates than did patients treated with venlafaxine XR or escitalopram during 6 months after medication initiation. Future studies should examine the clinical and economic implications of these differences.LimitationsThis study has limitations such as possible selection bias using secondary database analysis.

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