The association of race, comorbid anxiety, and antidepressant adherence among Medicaid enrollees with major depressive disorder

Background: Depressed patients often have comorbid anxiety. African-Americans with depression are less likely to adhere to antidepressant treatment. Knowledge of the association between race, comorbid anxiety, and adherence among Medicaid enrollees with depression is limited. Objective: The objective of this study was to evaluate the association of race, comorbid anxiety, and antidepressant adherence, and persistence among Medicaid enrollees with major depressive disorder (MDD). Methods: The MarketScan ^® Multi-State Medicaid Database (Thomson Reuters, Ann Arbor, MI) was used in this retrospective cross-sectional study. Medicaid enrollees aged between 18 and 64 years, with MDD but without bipolar disorders, and with a newly initiated antidepressant between January 1, 2004 and December 31, 2006 were identified. An index date was assigned corresponding to the newly initiated antidepressant. Patients having claims for any antidepressant refills during the 12 months before the index date were excluded. Eligible patients were then followed-up for 12 months after the index date. Adherence was measured by a modified medication possession ratio. Adherence was evaluated using multivariate logistic regression. Persistence was assessed based on treatment discontinuation and examined by Kaplan-Meier survival curves and Cox-propositional hazard regression models. Results: A total of 3083 Medicaid patients with MDD were included. Approximately, 25% of patients had comorbid anxiety. The odds of adhering to antidepressants were 40% lower among African-Americans than Caucasians, adjusting for covariates (AOR [adjust odds ratio]. =0.60; 95% confidence interval [CI]. =0.51-0.72, P< .001). MDD patients with comorbid anxiety were more likely to adhere to antidepressants than patients with MDD alone (AOR. =1.55, 95% CI. =1.27-1.90, P< .001). African-Americans had a higher hazard of not persistently taking antidepressants (hazard ratio. =1.47, 95% CI. =1.30-1.65, P< .001). The interaction between race and comorbid anxiety was not associated with adherence or persistence. Conclusions: Among Medicaid enrollees with MDD, race and comorbid anxiety disorders are significantly associated with antidepressant adherence and persistence. Physicians need to recognize comorbid anxiety and race as 2 important determinants of antidepressant use behaviors when they encounter Medicaid patients with MDD.