Effects of various factors on steady state plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine.

Effects of various factors on steady state plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine (mCPP) were studied in 43 depressed patients (19 males, 24 females) receiving trazodone 150 mg at bedtime for 1-3 weeks. Sixteen cases were smokers, and 19 cases were also receiving various benzodiazepines. The means (and ranges) of plasma concentrations of trazodone and mCPP, and the mCPP/trazodone ratio were 619 (251-1059) ng/ml, 59 (32-139) ng/ml and 0.100 (0.044-0.219), respectively. Smokers had significantly (p < 0.05) lower plasma concentrations of trazodone and higher mCPP/trazodone ratios than non-smokers. Age, sex and co-administration of benzodiazepines did not affect any plasma concentrations or the mCPP/trazodone ratio. In 11 cases where the dose was increased to 300 mg, neither plasma concentration/dose ratios nor the mCPP/trazodone ratio changed significantly. The present study thus suggests that: (1) there is a large Interindividual variation in the metabolism of trazodone; (2) smoking enhances the metabolism, but age, sex and co-administration of benzodiazepines do not affect it; (3) trazodone and mCPP have linear kinetics.