PHARMACOKINETIC INTERACTIONS - AMITRIPTYL INE, FLUOXETINE AND ANTITUBERCULOSIS DRUGS

Polytherapy is often used in clinical practice. The drug associations may lead to pharmacokinetic and/or pharmacodynamic interactions, with clinical implications. The authors reported a quantified illustration of 2 types of interactions in a depressed patient : between antidepres sants, amitriptyline and fluoxetine, between these antidepressants and antituberculosis. Firstly, when fluoxetine was added to amiptriptylin e, it was observed, as expected, an increase of the tricyclic and its metabolite plasma levels, despite a decrease of its dosage. Secondly, when antituberculosis were added to the 2 antidepressants, it was obse rved a decrease of the tricyclic drug plasma levels. These levels rema ined below the therapeutic window even when the tricyclic antidepressa nt dosage was increased. It seems that the fluoxetine interaction disa ppeared. The competition between the inhibitory effect of fluoxetine a nd the induction of rifampicin, on the metabolism of amitriptyline is discussed.