Determinants of direct cost differences among US employees with major depressive disorders using antidepressants

To understand factors driving the economic burden of major depressive disorder (MDD) patients with different treatment regimens, by evaluating the relationship between medical profiles and treatment costs.

Claims data for US privately insured employees (1999-2004) were analysed. Analysis included adult employees with >/=1 diagnosis of MDD and >/=1 prescription for specific antidepressants following a 6-month washout period. Patients were first classified into treatment pattern groups (switchers/discontinuers/maintainers/augmenters), then stratified into mutually exclusive treatment groups - nonstable, stable and intermediate - based on evidence of stability in treatment therapy. Rates of mental and physical co-morbidities, injuries/accidents, substance abuse and urgent care use were analysed across treatment pattern groups. Direct (medical/drug) costs were calculated per patient per year and disaggregated into depression- and non-depression-related components. A two-part multivariate model controlled for baseline characteristics. Costs were also estimated for patients with MDD only, patients with MDD and generalized anxiety disorder (GAD), and patients with MDD and any type of anxiety.

Annual per patient adjusted costs (year 2005 values) were significantly lower among stable patients ($US6215) than among intermediate ($US7317) and nonstable patients ($US9948; p < 0.001). Stable patients also had lower depression- and non-depression-related costs. Patients with MDD and comorbid GAD or any type of anxiety had significantly higher costs than MDD-only patients.

Nonstability of treatment is associated with higher comorbidity rates, more urgent care use and higher total, depression- and non-depression-related direct costs. The stable group represents continuity of care and is associated with significant cost savings. Co-morbidities are associated with increased costs.