Utilization, price, and spending trends for antidepressants in the US Medicaid Program

Antidepressants are often used in the treatment of major depressive disorder and other mental illnesses, and constitute one of the most widely prescribed and costly medication classes in the US Medicaid Program. However, antidepressant utilization and price patterns within this market have not yet been adequately characterized.

This study was undertaken to analyze antidepressant drug utilization and price trends and to quantify market-share competition in Medicaid.

Quarterly utilization and payment data were retrieved from the national Medicaid pharmacy claims files provided by the Centers for Medicare & Medicaid Services. Quarterly per-prescription prices were estimated by dividing the payment amounts by the number of prescriptions. Descriptive time series analysis was conducted to assess the trends of utilization, expenditures, market shares, and prices from January 1991 through December 2005, for 3 major antidepressant subclasses--Selective Serotonin Reuptake Inhibitors (SSRIs), Tricyclic Antidepressants, and Other Antidepressants--as well as for individual agents within these subclasses. Using exponential smoothing models, 3-year market-share forecasts were produced.

From 1991 to 2005, the total number of antidepressant prescriptions rose 380% from 6.82 million to 32.72 million. Total expenditures on antidepressants increased from $159 million in 1991 to $2.26 billion in 2004, then decreased to $1.99 billion in 2005, following the entry of lower-priced generic fluoxetine in 2001 and generic paroxetine in 2003. The payment market share for the SSRIs increased from 40% in 1991 to 82% in 1997, then decreased to 64% in 2005. It is projected to be 64% (95% confidence interval [CI]: 51-77%) in 2008 quarter 4.

Increases in antidepressant drug expenditures were primarily because of rising utilization; however, there was also some increase in average price per prescription for many of the antidepressants studied. Switching to generic drugs may offer significant cost-saving potential.