Determination of cefadroxil in rat plasma and urine using LC–MS/MS and its application to pharmacokinetic and urinary excretion studies

• We report the first LC–MS/MS assay for cefadroxil in rat plasma and urine.
• We demonstrated sufficient stability of cefadroxil in plasma and urine.
• The assay was successfully validated across the broad range of 10–10,000 ng/mL.
• The assay quantitated cefadroxil in plasma/urine samples for a study that had both oral and IV treated groups.

A simple, rapid, and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) was developed and validated for the determination of cefadroxil, a first-generation cephalosporin, in rat plasma and urine. Rat samples were deproteinized with methanol, and then injected into the LC–MS/MS system (electro-spray ionization, positive mode) for quantification. Drugs were separated on a Synergi™ 4 μm Polar-RP 80A column (150 mm × 2.0 mm, 4 μm) with a mixture of 0.1% formic acid and methanol (62:38, v/v) as the mobile phase at 0.2 mL/min. Detection was performed using multiple reaction-monitoring modes at m/z 364.1 → 208.1 (for cefadroxil) and m/z 368.1 → 174.2 (for cefaclor, the internal standard). Method was specific and linear over the concentration range of 10–10,000 ng/mL. Validation parameters for cefadroxil, including accuracy, precision, absolute matrix effect, and stability in rat plasma and urine, were acceptable according to the biological method validation guidelines of the FDA (2001) [16]. Cefadroxil levels in plasma up to 1440 min or 480 min and urine up to 96 h were quantifiable following oral and intravenous cefadroxil administrations to rats at a dose of 2 mg/kg, each, suggesting that the method is appropriate for routine pharmacokinetic studies including urinary recovery in rats.