Interindividual variations of desmethylation and hydroxylation of clomipramine in an Oriental psychiatric population.

We measured the concentrations of clomipramine and its metabolites, N-desmethylclomipramine, 8-hydroxy-N-desmethylclomipramine, and 8-hydroxyclomipramine in plasma in 92 Japanese psychiatric patients receiving clomipramine hydrochloride (Anafranil, Ciba-Geigy Japan Limited, Takarazuka, Japan) by high-performance liquid chromatography. Although there were large interindividual variations of total drug concentrations and concentrations of parent or intermediate metabolic compounds in plasma, significant positive correlations were observed between these drug concentrations and daily doses of clomipramine hydrochloride (milligrams per kilogram of body weight). The metabolic ratios for both desmethylation and hydroxylation varied substantially with 30- to 90-fold interindividual variations. Frequency distribution histograms and probit analyses of these parameters identified only one possible poor hydroxylator but no poor desmethylator of clomipramine. These results suggest that there are large interindividual variations of capacities for hydroxylation and desmethylation of clomipramine in the Oriental population and that therapeutic drug monitoring is essential in clinical practice to reduce the adverse effects of clomipramine and to prevent poor response to clomipramine.