Simultaneous determination of morinidazole, its N-oxide, sulfate, and diastereoisomeric N+-glucuronides in human plasma by liquid chromatography–tandem mass spectrometry

Morinidazole is a new third-generation 5-nitroimidazole antimicrobial drug. To investigate the pharmacokinetic profiles of morinidazole and its major metabolites in humans, a liquid chromatography–tandem mass spectrometry method was developed and validated for simultaneous determination of morinidazole, its N-oxide metabolite (M4-1), a sulfate conjugate (M7), and two diastereoisomeric N+-glucuronides (M8-1 and M8-2) in human plasma. A simple acetonitrile-induced protein precipitation was employed to extract five analytes and internal standard metronidazole from 50 μL human plasma. To avoid the interference from the in-source dissociation of the sulfate and achieve the baseline-separation of diastereoisomeric N+-glucuronides, all the analytes were separated from each other with the mobile phase consisting of 10 mM ammonium formate and acetonitrile using gradient elution on a Hydro-RP C18 column (50 mm × 2 mm, 4 μm) with a total run time of 5 min. The API 4000 triple quadrupole mass spectrometer was operated under the multiple reaction-monitoring mode using the electrospray ionization technique. The developed method was linear in the concentration ranges of 10.0–12,000 ng/mL for morinidazole, 1.00–200 ng/mL for M4-1, 2.50–500 ng/mL for M7, 3.00–600 ng/mL for M8-1, and 10.0–3000 ng/mL for M8-2. The intra- and inter-day precisions for each analyte met the accepted value. Results of the stability of morinidazole and its metabolites in human plasma were also presented. The method was successfully applied to the clinical pharmacokinetic studies of morinidazole injection in healthy subjects, patients with moderate hepatic insufficiency, and patients with severe renal insufficiency, respectively.

► Simultaneously determine morinidazole and its four metabolites in human plasma.
► Gradient elution was used to obtain the resolution of two N+-glucuronide isomers.
► The potential interference from the in-source dissociation of the conjugates was avoided.
► The method was applied to clinical pharmacokinetic studies of morinidazole injection.