Determination of clarithromycin in human plasma by LC-MS method

Aim: To develop an LC-MS method for the determination of clarithromycin concentration in human plasma. Method: 20 μl of roxithromycin solution(10 μg/ml, internal standard) was added to 0.20 ml of plasma. The plasma samples were extracted with 4 ml ether after alkalizing using 0.1 mol/L Na₂CO₃. Three ml of organic layer was transferred to clean tube and evaporated to dryness under N₂. The residue was reconstitued in 1 ml acetonitrile and 10 μl was injected into an ODS C₁₈ (5 μm, 250 mm × 2.0 mm) column. The mobile phase consisted of acetonitrile: 0.05% acetic acid (60:40 v/v) at flow rate of 0.2 ml/min. The eluate from the HPLC column was plumbed directly into ESI probe. Analysis in the mass spectrometer was operated in the selected-ion monitoring model. The mass spectrometers was operated in SIM m/z 748.5 for clarithromycin,837.5 for roxithromycin and 764.5 for 14-hydroxylclarthromycin. Result: Recoveries of clarithromycin at 0.125, 1.00 and 8.00 μg/ml were 86.5%, 98.9% and 98.5% respectively. The standard curve was linear in the range of 0.0625 - 8.00 μg/ml. The relative standard derivation of intra-day and inter-day was smaller than 17%. Conclusion: The method of LC-MS is suitable for pharmacokinetic study of clarithromycin in human plasma.