An evaluation of the CYP2D6 and CYP3A4 inhibition potential of metoprolol metabolites and their contribution to drug-drug and drug-herb interaction by LC-ESI/MS/MS.

The aim of the present study was to evaluate the contribution of metabolites to drug-drug interaction and drug-herb interaction using the inhibition of CYP2D6 and CYP3A4 by metoprolol (MET) and its metabolites. The peak concentrations of unbound plasma concentration of MET, α-hydroxy metoprolol (HM), O-desmethyl metoprolol (ODM) and N-desisopropyl metoprolol (DIM) were 90.37 ± 2.69, 33.32 ± 1.92, 16.93 ± 1.70 and 7.96 ± 0.94 ng/mL, respectively. The metabolites identified, HM and ODM, had a ratio of metabolic area under the concentration-time curve (AUC) to parent AUC of ≥0.25 when either total or unbound concentration of metabolite was considered. In vitro CYP2D6 and CYP3A4 inhibition by MET, HM and ODM study revealed that MET, HM and ODM were not inhibitors of CYP3A4-catalyzed midazolam metabolism and CYP2D6-catalyzed dextromethorphan metabolism. However, DIM only met the criteria of >10% of the total drug related material and <25% of the parent using unbound concentrations. If CYP inhibition testing is solely based on metabolite exposure, DIM metabolite would probably not be considered. However, the present study has demonstrated that DIM contributes significantly to in vitro drug-drug interaction. Copyright © 2016 John Wiley & Sons, Ltd.

Plasma protein binding, pharmacokinetics, tissue distribution and CYP450 biotransformation studies of fidarestat by ultra high performance liquid chromatography-high resolution mass spectrometry.

Fidarestat, an aldose reductase inhibitor, has been used for the treatment of the diabetic associated complications such as retinopathy, neuropathy and nephropathy. To better understand the metabolism and pharmacokinetics of fidarestat, we have evaluated plasma protein binding, pharmacokinetics, tissue distribution of the drug and its conjugated metabolites and CYP450 biotransformation by liquid chromatography-high resolution mass spectrometry. Effective chromatographic separation of fidarestat and hydrochlorothiazide (IS) in rat plasma and tissues was achieved on Hypersil gold C-18 column in an isocratic elution mode. For detection, a high-resolution Orbitrap mass spectrometer with heated electrospray ionization inlet in the negative ion mode was used. High-resolution extracted ion chromatograms for each analyte were obtained by processing the full-scan MS mode with 5 ppm mass tolerance. The impact of plasma protein binding with the drug and conjugated metabolites of the drug on pharmacokinetics has been determined. The study indicated that 9.5% of free form of fidarestat may be pharmacologically active and the Cmax for free fidarestat was found to be 80.30 ± 6.78 ng/mL. The AUC0-t and AUC0-∞ were found to be 185.46 ± 32 and 195.92 ± 15.06 ng h/mL, respectively. Among tissues, the maximum observed distribution was found to be in kidney followed by liver and heart. Docking experiments and in vitro CYP450 reaction phenotyping revealed that two CYP1A2 and CYP2D6 are involved in the phase I metabolism of fidarestat. Oxidative deamination and N/O glucuronidation are the major phase I and phase II metabolites, respectively. In vitro CYP450 inhibition assay of fidarestat for drug-drug interaction showed weak inhibition and may not alter pharmacokinetics, distribution or clearance of other co-administered drug.