Liquid chromatography–tandem mass spectrometry for the determination of methylprednisolone in rat plasma and liver after intravenous administration of its liver-targeted dextran prodrug

A specific and sensitive liquid chromatography (LC)–tandem mass spectrometric method for quantitative determination of methylprednisolone (MP) in rat plasma and liver was developed and validated using triamcinolone acetonide as an internal standard. Liquid–liquid extraction using tert-butyl methyl ether was used to extract the drug and the internal standard from plasma and liver. The separation of MP was performed on a C18 column with a mobile phase of acetonitrile:0.5% formic acid aqueous solution (85:15, v/v) over 4 min. The assay was based on the selected reaction monitoring transitions at m/z 375 → 161 for MP in plasma, 375 → 357 for MP in liver, and 435 → 415 for internal standard in both plasma and liver. The lower limit of quantification was 20 ng/mL based on 100 μL of plasma or liver homogenate. Intra- and inter-day assay variations were ≤15%, and the accuracy values were between 85.8% and 118%. The extraction recoveries ranged from 76.8% to 79.2% for plasma and 76.8–80.8% for liver across the calibration curve range. The method was successfully applied to the measurement of low concentrations of regenerated MP in plasma and liver after intravenous administration of a single dose (5 mg/kg) of a liver-targeted dextran prodrug of MP to rats.