Determination of zanamivir in rat and monkey plasma by positive ion hydrophilic interaction chromatography (HILIC)/tandem mass spectrometry

A hydrophilic interaction chromatography (HILIC)/mass spectrometric assay was developed for the determination of zanamivir, a neuraminidase inhibitor used to treat influenza, in rat and monkey plasma. An organic solvent with hydrophilic properties, methanol, was used to precipitate proteins in plasma to assure the highly polar zanamivir of staying in solution. Chromatographic separation was obtained using a HILIC silica column with multiple reaction monitoring turboionspray positive ion detection. The stable label of zanamivir, [13C1 15N2] GR121167C, was used as the internal standard. The assay was validated for the determination of zanamivir in rat and monkey plasma. The lower and upper limits of quantitation were 2 and 10000 ng/mL, using 0.05 mL plasma aliquot, respectively. The signal to noise ratio of a typical 2 ng/mL was ∼5:1. The inter-day precision (relative standard deviation) and accuracy (relative error) in rat plasma, derived from the analysis of validation samples at 5 concentrations, ranged from 6 to 10% and −6.5 to 0.2%, respectively. The inter-day precision (relative standard deviation) and accuracy (relative error) in monkey plasma, derived from the analysis of validation samples at five concentrations, ranged from 2 to 8% and −2.3 to 2.1%, respectively. Zanamivir was found to be stable for at least 5 days at approximately −80 °C and at room temperature in plasma. This assay incorporates a simple protein precipitation with methanol and hydrophilic interaction chromatography which is sensitive, accurate, precise, and is being used to support oral formulation and toxicokinetic studies in rat and monkey, respectively.