Development of a HPLC method for the determination of cyclosporin-A in rat blood and plasma using naproxen as an internal standard

An isocratic reversed phase high-performance liquid chromatographic (HPLC) method with ultraviolet detection at 205 nm has been developed for the determination of cyclosporin-A (CyA) in rat blood and plasma. Naproxen was successfully used as an internal standard. Blood or plasma samples were pretreated by liquid–liquid extraction with diethyl ether. The ether extract was evaporated and the residue was reconstituted in acetonitrile–0.04 M monobasic potassium phosphate buffer (pH 2.5) solvent mixture. After washing with n-hexane, 30 μl of the reconstituted solution was injected into HPLC system. Good chromatographic separation between CyA and internal standard peaks was achieved by using a stainless steel analytical column packed with 4 μm Nova-Pak Phenyl material. The system was operated at 75 °C using a mobile phase consisting of acetonitrile–0.04 M monobasic potassium phosphate (pH 2.5) (65:35 v/v) at a flow rate of 1 ml/min. The calibration curve for CyA in rat blood was linear over the tested concentration range of 0.0033–0.0166 M with a correlation coefficient of 0.989. For rat plasma, the range of the concentrations tested were between 0.002 and 0.0166 M and showed linearity with a correlation coefficient of 0.953. The intra- and inter-run precision and accuracy results were 1.24–21.87 and 3.1–12.23%, respectively. The low volume of blood or plasma needed (200 μl), simplicity of the extraction process, short run time (5 min) and low injection volume (30 μl) make this method suitable for quick and routine analysis.