Development of a high-performance liquid chromatographic-electrospray mass spectrometric assay for the specific and sensitive quantification of the novel immunosuppressive macrolide 40-O-(2-hydroxyethyl)rapamycin.

It was our objective to develop a rapid, sensitive and specific assay to quantify the immunosuppressive macrolide 40-O-(2-hydroxyethyl)rapamycin (SDZ-RAD) in blood of transplant patients. SDZ-RAD was extracted from blood by solid-liquid extraction. SDZ-RAD and its internal standard 28,40-diacetyl rapamycin were quantified using HPLC-electrospray MS. The assay was linear from 0.1 to 100 microg/l (r2 = 0.99). The mean recovery was 83% for SDZ-RAD and 80.5% for the internal standard. The mean day-to-day precision was 8.0%. Extracted samples were stable at 20 degrees C for at least 48 h and SDZ-RAD blood samples at -80 degrees C for at least six months.