Characterization of a new norfloxacin metabolite monitored during a bioequivalence study by means of mass spectrometry and quantum computation

Abstract

A bioequivalence study of two formulations containing norfloxacin was used for identification and assay of the metabolite of norfloxacin in human serum samples. The bioequivalence study was based on an analytical method using liquid chromatography with fluorescence detection. The plasmatic profile of metabolite was similar to norfloxacin for both formulations. Three plasma fractions of norfloxacin metabolite from a volunteer were isolated by liquid chromatography and investigated by atmospheric-pressure chemical ionization mass-spectrometry. The structure of norfloxacin metabolite (7-aminoethylenamino-6-fluoro-4-hydroxy quinoline-3-carboxylic acid) was identified taking into account also the mass spectrometry investigations achieved for norfloxacin and ciprofloxacin (used as internal standard for the analytical method). A theoretical procedure based on quantum chemical calculations has been also used to explain the mass fragmentation in molecules of norfloxacin metabolite that differ from the molecule of norfloxacin.

Considerations for Metabolite Pharmacokinetic Data in Bioavailability/Bioequivalence Assessments

“…Inthe liquid chromatographicfluorescenceassaydeveloped tosupport the bioequivalencestudyof norfloxacin (CAS 70458-96-7),the authors wereable toi dentifyanothermajorpeakf rom the in vivostudys amplesin healthysubjects [43].Itappeared thatthe plasmaticprofile of thisnewpeakwassimilarbetween the twoformulations.Thisled toadetailed investigation using liquid chromatographyatmospheric-pressurechemicalionization mass-spectrometry.Using the chemicalstructuresof bothnorfloxacin and ciprofloxacin (CAS 85721-33-1) and the respectivef ragmentation sequencing and patterns, the authors wereable toidentifythe structureofthe new metabolitepeakas7-aminoethylenamino-6-fluoro-4-hydroxy quinoline-3-carboxylicacid [43].…”

Applicability of LC/MS/MS assay for 6‐methoxy‐2‐napthylacetic acid to support the bioequivalence study of nabumetone—comments on the research work of Patel et al. (2008)

“…Applicability of LC/MS/MS assay for 6-methoxy-2-napthylacetic acid to support the bioequivalence study of nabumetonecomments on the research work of Patel et al (2008) To the EditorIn recent years, many publications have appeared in BMC that utilize state of the art laboratory tools for development and validation of assays for the applicability to bioequivalence studies in human volunteers (Georgita et al, 2008;Patel et al, 2008;Medvedovici et al, 2008;Sora et al, 2007;Nirogi et al, 2006). Interestingly, all of these published assays support both parent and/or active metabolite(s) exposure measurements to facilitate pharmacokinetic characterization and/or bioequivalence assessment of the derived parameters between test and reference products.…”