SENSITIVE DETERMINATION OF ERYTHROMYCIN IN HUMAN PLASMA BY LC-MS MS/

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the analysis of erythromycin in human plasma (EDTA as anticoagulant) was developed and validated. The concentration ranges were 0.5-50 and 50-5000 ng ml(-1). The procedure involved alkalization of 0.5 ml of pl asma, one step liquid-liquid extraction, dryness of the extract and re constitution in 80:20 water:acetonitrile. An Inertsil ODS-2 5 mu m, 3. 0 x 50 mm column (Metachem) with a C-8 guard column and isocratic mobi le phase were used for liquid chromatography. The mobile phase consist ed of 1:1 acetonitrile:water with 2 mM NH4OAc and 0.1% HOAc. A flow ra te of 0.7 ml min(-1) was used. The analysis time on LC-MS/MS for one s ample was approximate to 2 min. A Turbo-Ionspray source was interfaced between the HPLC and triple quadrupole mass spectrometer (Sciex API I II Plus). MS/MS analysis used Multi-Reaction Monitoring (MRM) mode. Th e lowest limit of quantitation (LOQ) was 0.5 ng ml(-1) with all Qualit y Control (QC) sample recoveries varying between 88 and 105%. Nine int raday and interday calibration curves were generated yielding correlat ion coefficients ranging from 0.995 to 1.000. Average recovery for ery thromycin at 1 ng ml(-1) was 105% (+/-4.5%). Average recovery for the internal standard was 83-103%. Short-term and long-term stability in t he freezer (-20 degrees C), bench stability, and stability after 3 fre eze/thaw cycles at -20 and -80 degrees C were conducted. The samples w ere found to be stable under all conditions. The method developed and validated proved useful for clinical pharmacokinetic study sample anal ysis with high throughput due to its high sensitivity and very short a nalysis time. (C) 1998 Elsevier Science B.V. All rights reserved.