Plasma concentrations of trazodone and m-chlorophenylpiperazine at steady state can be predicted from those after an initial dose of trazodone.

1. The authors studied the correlations between plasma concentrations of trazodone and mCPP at steady state and those after an initial dose of trazodone. 2. Fifteen depressed patients received trazodone 150 mg at bedtime for 3 weeks, and blood samplings were taken 12 h after the initial dose and 12 h after the last dose at each week. Plasma concentrations of trazodone and mCPP were measured by high-performance liquid chromatography. 3. Plasma concentration of mCPP, but not trazodone, was significantly higher at each week than after initial dosing. 4. For both trazodone and mCPP, significant linear relationships were found between plasma concentration after initial dosing and the average of 3 weeks' plasma concentrations. 5. The present study thus suggests that plasma concentrations of trazodone and mCPP at steady state can be predicted from those after an initial dose of trazodone.