Increased plasma tricyclic antidepressant concentrations in two patients concurrently treated with fluoxetine.

Two patients taking stable doses of standard tricyclic antidepressants were additionally treated with fluoxetine as the first step in a transition to that drug. After fluoxetine was added, both patients' plasma tricyclic antidepressant levels increased substantially. Adverse side effects occurred in one patient. Fluoxetine may increase the plasma levels of standard tricyclic antidepressants and the likelihood of tricyclic antidepressant toxicity.