Determination of cyclosporine in saliva using liquid chromatography-tandem mass spectrometry

Saliva may offer an alternative specimen for the therapeutic monitoring of cyclosporine (CsA) in children and patients with difficult venous access. For a highly protein-bound drug such as CsA, saliva may also provide a practical approach for measuring the unbound concentration. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is ideally suited for the measurement of drugs in saliva. A solid-phase extraction technique, analytic liquid chromatography over an Aqua Perfect C18 column, maintained at 65 degrees C, and electrospray tandem mass spectrometry were used to quantify CsA in saliva. The method used cyclosporine C (CsC) as the internal standard. Mobile phase comprised of a 97:3 vol/vol mixture of methanol and 30 mmol ammonium acetate at a flow rate of 0.5 mL/min. Chromatograms using mass transitions of m/z 1219.9 --> m/z 1202.9 for CsA and m/z 1235.9 --> m/z 1218.9 for CsC were obtained. The calibration curve was linear from 1 to 300 microg/L with correlation coefficient values ranging from 0.9732 to 0.9968). The lower limit of quantification was 1 microg/L, and limit of detection was 0.6 microg/L with an average extraction recovery of 84.7 +/- 2.6% for CsA and 93.7 +/- 4.4% for CsC from the saliva matrix. The accuracy of the method ranged from 92% to 104.7%, and the intra- and interrun coefficients of variation were 6.9-12.2% and 8.3-12.1%, respectively. The correlation coefficient value between the CsA concentration measurements in 15 paired blood-saliva samples from kidney transplant recipients was 0.695 (P = 0.006). The noninvasive and simple method of saliva collection coupled with the LC-MS/MS quantification technique for CsA analysis would generate novel data that could benefit patients undergoing CsA therapy.