ObjectiveTo compare the pharmacokinetics of milnacipran in extensive metabolisers (EMs) and poor metabolisers (PMs) of sparteine and mephenytoin, and to assess the influence of multiple administrations of milnacipran on the activity  of  cytochrome  P450  (CYP)  isoenzymes  through  its  own  metabolism and through various probes, namely CYP2D6 (sparteine/dextromethorphan), CYP2C19 (mephenytoin), CYP1A2 (caffeine) and CYP3A4 (endogenous 6-β-hydroxy-cortisol excretion).MethodsTwenty-five healthy subjects, 12 EMs for both sparteine/dextromethorphan and mephenytoin, nine EMs for mephenytoin and PMs for sparteine/dextromethorphan (PM2D6) and four PMs for mephenytoin and EMs for sparteine/dextromethorphan (PM2C19) were administered milnacipran as a single 50mg capsule on day 1 followed by a 50mg capsule twice daily for 7 days. The pharmacokinetics of milnacipran and its oxidative metabolites were assessed after the first dose (day 1) and after multiple administration (day 8), and were compared for differences between CYP2D6 and CYP2C19 PMs and EMs. Metabolic tests were performed before (day −2), during (days 1 and 8) and after (day 20) milnacipran administration.ResultsMilnacipran steady state was rapidly achieved. Metabolism was limited: approximately 50% unchanged drug, 30% as glucuronide and 20% as oxidative metabolite (mainly F2800 theN-dealkyl metabolite). Milnacipran administration to PM2D6and PM2C19subjects did not increase parent drug exposure or decrease metabolite exposure. Milnacipran oxidative metabolism is not mediated through CYP2D6 or CYP2C19 polymorphic pathways nor does it significantly interact with CYP1A2, CYP2C19, CYP2D6 or CYP3A4 activities.ConclusionLimited reciprocal pharmacokinetic interaction between milnacipran and CYP isoenzymes would confer flexibility in the therapeutic use of the drug when combined with antidepressants. Drug-drug interaction risk would be low, even if the combined treatments were likely to inhibit CYP2D6 and CYP2C19 isoenzyme activities.