Everolimus is an immunosuppressant requiring routine monitoring in whole blood. We evaluated the analytical performance of a new immunoassay for everolimus, Quantitative Microsphere System (QMS) everolimus (Thermo Fisher Scientific), which is CE marked and currently under review by Food and Drug Administration of the United States by comparing results with values obtained by using liquid chromatography/mass spectrometry. The total coefficient of variations (CVs) were 8.3% for low control (mean: 3.8 ng/mL), 6.1% for the medium control (mean: 8.0 ng/mL), and 7.5% for the high control (mean: 14.4 ng/mL) (n = 80 for each control, run over 20 nonconsecutive days). The respective total CVs for patients' pool were 13.3% (mean: 4.0 ng/mL), 7.5% (mean: 8.2 ng/mL), and 8.7% (mean: 11.7 ng/mL) (n = 80 for each patient pool). The assay was linear from a whole-blood everolimus level between 1.5 and 20 ng/mL, and the limit of quantitation was 1.3 ng/mL. Comparison was carried out using 90 renal transplant patient samples, and we observed the following Passing and Bablok linear regression plot: y = 1.11, slope = -0.005 (R = 0.92). This assay was not affected by commonly used 70 drugs, but sirolimus, a drug structurally similar to everolimus, showed 46% cross-reactivity. We conclude that QMS everolimus immunoassay has adequate sensitivity and specificity for the determination of whole-blood everolimus and can be used for routine therapeutic drug monitoring.
An isocratic reversed-phase high performance liquid chromatographic method for the determination of tamoxifen and its metabolites in plasma and tissues is described. Plasma or tissue homogenate was extracted with methanol/dimethyl sulphoxide (4:1 v/v). The supernatant after centrifugation was separated on a BDS-Hypersil column with methanol/0.5 M ammonium acetate (75:25 v/v) as the mobile phase. The recoveries of tamoxifen added to plasma and liver tissue homogenate by the extraction procedure were 102 +/- 1.6 and 98 +/- 2.4% (mean +/- SD, n = 6), respectively. The solutes were detected at 280 nm with a detection limit of 0.25 micrograms/mL for tamoxifen.
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