Sensitive LC-ESI/MS/MS assay for the quantification and pharmacokinetic study of roxithromycin in human serum

A simple and sensitive LC-ESI/MS/MS method is developed and evaluated to determine the concentrations of roxithromycin in human serum. Serum proteins are precipitated with methanol with clarithromycin as the internal standard. In order to reduce the pollution of sample, after vortex mixing and centrifugation, the supernatants are diluted with mobile phase before analysis on a Phenomenex Luna CN column (100 mm x 2.0mm i.d., 3 mu m). The mobile phase composes of methanol, acetonitrile and 0.1% formic acid and 0.1% ammonium acetate in water (3: 3: 4, v/v/v) at a flow rate of 0.2 mL/min. The linearity ranges from 10 to 20480 ng/mL. The extraction recoveries of roxithromycin range from 97 to 101%. The method is successfully used to pharmacokinetic study of roxithromycin after an oral administration dose of 300 mg roxithromycin tablets to 20 healthy volunteers.