High pressure liquid chromatographic determination of cyclosporin A in plasma

A sensitive and rapid high performance liquid chromatographic method was developed for the determination of Cyclosporin A in plasma. Cyclosporin A was isolated from methanol-precipitated plasma using miniature compressed silica reverse-phase columns (Sep-Paks). In the method, 1 ml serum is precipitated in 3 ml methanol. After centrifugation 2 ml of supernatant is diluted in 1 ml water and the sample flushed through a washed Sep-Pak. The sample on the miniature column is washed with water and 75% v/v methanol, and Cyclosporin A is eluted in 1 ml methanol. At least 80% of the drug is recovered. Samples are analyzed on a reverse-phase column, the mobile phase is methanol:water (95:5) and detection is conducted at 205 nm. The detection limits were less than 100 ng/ml, but in plasma some interference was observed, especially at concentrations below 1000 ng/ml.