Tricyclic antidepressant plasma levels after fluoxetine addition

After a review of a pharmacokinetic interaction between tricyclic antidepressants (TCA) and fluoxetine the authors report their own data. They confirm the existence of an interaction of TCA with fluoxetine, in clinical practice, but the fluoxetine was not associated in all cases with a marked increase of TCA plasma levels. The increase appeared especially high with clomipramine (n = 4) and imipramine (n = 3), and lower or dose-dependent with amitriptyline (n = 4). The pharmacokinetic change did not induce side effects in the patients, even when the total TCA plasma level increased to 965 (clomipramine) or 785 (imipramine) ng/ml. The authors then discuss the clinical implication and the possible mechanism of action.