Evidence for a linear relationship between plasma trazodone levels and clinical response in depression in the elderly.

To investigate a possible relationship between plasma levels of trazodone and its clinical antidepressant effects, 11 elderly depressed patients underwent a 5-week treatment with 150 mg/day trazodone in three oral administrations. Clinical antidepressant response was assessed with two different clinical improvement criteria and plasma trazodone concentrations were determined by high-performance liquid chromatography. A significant correlation was found between steady-state plasma trazodone levels and its antidepressant efficacy, but not between plasma drug levels and the incidence of side effects. Moreover, the steady-state plasma trazodone concentration of 650 ng/ml was identified as threshold value for a greater occurrence of good antidepressant responses.