Stereoselective Inhibition of CYP2C19 and CYP3A4 by Fluoxetine and Its Metabolite: Implications for Risk Assessment of Multiple Time-Dependent Inhibitor Systems

Abstract

Recent guidance on drug-drug interaction (DDI) testing recommends evaluation of circulating metabolites. However, there is little consensus on how to quantitatively predict and/or assess the risk of in vivo DDIs by multiple time-dependent inhibitors (TDIs) including metabolites from in vitro data. Fluoxetine was chosen as the model drug to evaluate the role of TDI metabolites in DDI prediction because it is a TDI of both CYP3A4 and CYP2C19 with a circulating N-dealkylated inhibitory metabolite, norfluoxetine. In pooled human liver microsomes, both enantiomers of fluoxetine and norfluoxetine were TDIs of CYP2C19, (S)-norfluoxetine was the most potent inhibitor with time-dependent inhibition affinity constant (K I ) of 7 mM, and apparent maximum time-dependent inhibition rate (k inact,app ) of 0.059 min 21. Only (S)-fluoxetine and (R)-norfluoxetine were TDIs of CYP3A4, with (R)-norfluoxetine being the most potent (K I = 8 mM, and k inact,app = 0.011 min 21).Based on in-vitro-to-in-vivo predictions, (S)-norfluoxetine plays the most important role in in vivo CYP2C19 DDIs, whereas (R)-norfluoxetine is most important in CYP3A4 DDIs. Comparison of two multiple TDI prediction models demonstrated significant differences between them in in-vitro-to-in-vitro predictions but not in in-vitro-to-in-vivo predictions. Inclusion of all four inhibitors predicted an in vivo decrease in CYP2C19 (95%) and CYP3A4 (60-62%) activity. The results of this study suggest that adequate worst-case risk assessment for in vivo DDIs by multiple TDI systems can be achieved by incorporating time-dependent inhibition by both parent and metabolite via simple addition of the in vivo time-dependent inhibition rate/cytochrome P450 degradation rate constant (l/k deg ) values, but quantitative DDI predictions will require a more thorough understanding of TDI mechanisms.

Fluoxetine- and Norfluoxetine-Mediated Complex Drug–Drug Interactions: In Vitro to In Vivo Correlation of Effects on CYP2D6, CYP2C19, and CYP3A4

“…All reference materials were obtained from Sigma Aldrich (St Louis, MO), Toronto Research Chemicals (North York, Ontario Canada), and Cerilliant (Round Rock, TX), except norfluoxetine stereoisomers, which were synthesized in house 3 . Concentrations of omeprazole, 5‐hydroxyomeprazole, dextromethorphan, dextrorphan, dextrorphan‐ O ‐glucuronide, midazolam, and caffeine in plasma and urine were analyzed using a Shimadzu Prominence UHPLC system (Shimadzu, Tokyo, Japan) coupled to an AB Sciex API3200 MS/MS system (AB Sciex, Framingham, MA), as described previously 3 , 22 . Cortisol, cortisone, 6β‐hydroxycortisol, 6β‐hydroxycortisone, lovastatin, and hydroxylovastatin acid were analyzed using an Agilent 1290 UHPLC (Agilent, Santa Clara, CA) coupled to an AB Sciex API5500 MS/MS system.…”

“…1,2 Fluoxetine and norfluoxetine enantiomers are reversible and time-dependent inhibitors of multiple cytochrome P450 (CYP) enzymes in vitro 3,4 Fluoxetine is predicted to cause strong inhibition of CYP2D6 and CYP2C19, and at least moderate inhibition of CYP3A4 in vivo. 3 However, existing in vivo data show a striking discrepancy with these predictions. In vivo, fluoxetine is a strong CYP2D6 inhibitor (7.8-fold increase in desipramine area under the concentration-time curve (AUC)) 5 and a moderate CYP2C19 inhibitor (2.9-fold increase in lansoprazole AUC).…”

Selective Serotonin Reuptake Inhibitor Drug Interactions in Patients Receiving Statins

“…S-fluoxetine and R-norfluoxetine inhibit CYP3A4 in vitro, and the combined fluoxetine and norfluoxetine enantiomer moiety is predicted to reduce in vivo CYP3A4 activity by about 60%. 33 However, in clinical doses administered to healthy volunteers, 11 days of treatment with fluoxetine elicited no significant inhibition of CYP3A4 activity as studied using erythromycin and alprazolam as substrates. 34 Fluoxetine (20-60 mg/d) did not influence the pharmacokinetics of the CYP3A4 substrate midazolam, either.…”

Contribution of Major Metabolites toward Complex Drug-Drug Interactions of Deleobuvir: In Vitro Predictions and In Vivo Outcomes

“…This equation was modified to incorporate multiple perpetrators in an additive manner as depicted in eq. (4) (Lutz et al, 2013;Rowland and Yeo et al, 2010). Clinical Drug-Drug Interaction Study.…”