Metabolic interaction between fluoxetine and clomipramine: a case report.

An 83-year-old patient suffering from a depressive episode was treated with a combination of clomipramine and fluoxetine. As no marked improvement was observed and cardiac side-effects were observed, a blood sample was taken for therapeutic drug monitoring. The result showed that the concentrations of clomipramine and desmethylclomipramine were very high (i.e. in the subtoxic range). A metabolic interaction was suspected and both antidepressants were immediately discontinued. Over time, concentrations of clomipramine and its metabolite decreased slowly and, simultaneously, the mood improved and side-effects disappeared. When clomipramine and desmethylclomipramine concentrations reached the lower limit of the optimal therapeutic range, monotherapy was restarted with clomipramine, and the patient improved enough to be discharged from the hospital.