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°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 μg/L with correlation coefficient values ranging from 0.9732 to 0.9968). The lower limit of quantification was 1 μg/L, and limit of detection was 0.6 μg/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