Automated simultaneous quantification of the immunosuppressants 40-O- (2-hydroxyethyl) rapamycin and cyclosporine in blood with electrospray-mass spectrometric detection

Abstract

A new analytical method to quantify 40-O-(2-hydroxyethyl)rapamycin (SDZ RAD) and cyclosporine (Cs) simultaneously in blood is presented. The combination of an on-line solid-phase extraction step with an HPLC system coupled to an electrospray mass spectrometer gave excellent specificity, sensitivity, and reproducibility. Aliquots of deproteinized blood samples were injected into the HPLC system and extracted on-line, using a conventional C18 guard column. The extract was eluted from the guard column in the backflush mode and injected into the liquid chromatography-mass spectrometry system. The calibration functions for SDZ RAD and Cs extracted from blood with added analyte were linear from 0.15 to 30 μg/L (r2 = 0.999) and from 1.5 to 1000 μg/L (r2 = 0.999), respectively. The CVs of peak areas were 6.2% at 10 μg/L SDZ RAD (n = 6) and 6.2% at 100 μg/L Cs (n = 6). Recovery ranged from 84.3% to 102.3% for SDZ RAD and from 81.7% to 92.2% for Cs. The lower limit of detection for both drugs was 0.05 μg/L. A rate of four samples per hour was maintained during the consecutive analysis of SDZ RAD and Cs in >500 blood samples with one single extraction and analytical column. The method described is a powerful tool for the simultaneous determination of SDZ RAD and Cs in blood. It works without time-consuming sample preparation steps and with excellent reproducibility. Because of the detection performance of electrospray mass spectrometry, this system offers flexibility in the working range, which is essential for therapeutic drug monitoring under different conditions.