Implications of an SSRI generic step therapy pharmacy benefit design: an economic model in anxiety disorders.

As the antidepressant market continues to expand, it is important for healthcare decision makers to develop clinically and economically sound drug benefit designs. As such, the purpose of this study was to determine the economic implications of a generic step therapy (GST) formulary compared with an open formulary for selective serotonin reuptake inhibitors (SSRIs) in patients with anxiety disorders. A model simulating the SSRI treatment patterns of patients diagnosed with an anxiety disorder in a hypothetical health plan with 1 million members was developed. Treatment options were generic SSRI agents (ie, fluoxetine, paroxetine immediate release, and citalopram) and branded SSRI agents (ie, sertraline, paroxetine controlled release, and escitalopram). After treatment initiation, patients could achieve 180 days or more of continuous therapy with no evidence of therapy change, achieve less than 180 days of therapy with no evidence of therapy change, or have a change in therapy. Consequently, patients incurred differential average annual medical and prescription costs. Model probabilities and costs were estimated from published literature and database analyses. The GST formulary resulted in a greater frequency of therapy change than the open formulary (41.3% vs 36.8%) and a lower frequency of continuous therapy for at least 6 months (25.3% vs 29.8%). Costs of SSRI medication were lower for the GST formulary than for the open formulary (11.6 million US dollars vs 14.8 million US dollars ). Medical costs were considerably greater for the GST formulary than for the open formulary, however (178.7 US dollars million vs 174.9 million US dollars, respectively), with a total cost of 190.3 US dollars million for the GST formulary versus 189.6 US dollars million for the open formulary. The incremental cost of implementing a GST formulary over 1 year was 684 360 US dollars , or 0.06 US dollars per member per month. A sensitivity analysis indicated that the model was most sensitive to changes in the cost of SSRI drug therapy and the average annual medical costs for patients with evidence of therapy change. The results of this model indicate that implementing a GST formulary for SSRIs in patients with anxiety disorders may be associated with an increased amount of therapy change and early treatment discontinuation, resulting in an overall cost increase to a health plan.