Determination of (15 R)- and (15 S)-15-methylprostaglandin E 2 in human plasma with picogram per milliliter sensitivity by column-switching high-performance liquid chromatography

Abstract

(15 R)-15-Methylprostaglandin E 2 (PGE 2) is a pro-drug under evaluation for the treatment of acute upper gastrointestinal hemorrhage and gastrointestinal cytoprotection. It is converted in acid (e.g., gastric fluid) to its active 15 S epimer. Both epimers are found in human plasma at low pg/ml levels following oral dosing. A high-performance liquid chromatographic (HPLC) method was developed for the simultaneous analysis of (15 R)- and (15 S)-15-methyl-PGE 2 in human plasma. The method combined off-line solid-phase extraction and reversed-phase HPLC clean-up with panacyl bromide derivatization and subsequent analysis using a heteromodal column-switching technique. Assay linearity was demonstrated over a range of 10–200 pg/ml for both 15-methyl-PGE 2 epiemers ( r ?> 0.995). There were no significant inter-day differences in assay results for either epimer at 50 and 25 pg/ml ( p > 0.05), with pooled estimates of precision at these levels producing relative standard deviations of ??< 8% and ??< 12%, respectively. The method quantitation limit (signal-to-noise ratio 5:1) for both epimers was 10 pg/ml when processing 3 ml of plasma. The analysis procedure was shown to be useful for quantifying at or below 10% of the (15 R)-15-methyl- PGE 1 maximum plasma concentration following a 50-μg oral dose in three human volunteers. For the same three subjects, however, the plasma concentration of (15 S)-15- methyl-PGE 2 did not exceed the quantitation limit of 10 pg/ml.