A sensitive and specific high performance liquid chromatographic assay for milrinone in rat and human plasma using a commercially available internal standard and low sample volume

To develop an alternate high performance liquid chromatographic method (HPLC) for the analysis of the positive inotropic agent, milrinone, in rat and human plasma. To plasma samples (0.1 mL), containing milrinone and the commercially available internal standard, amrinone, were added 0.15 mL of water and 0.35 mL of acetonitrile. Tubes were briefly vortex-mixed and centrifuged. The supernatant was transferred to clean tubes and 3 mL of methanol: diethyl ether (5:95) was added. The tubes were vortex mixed, centrifuged, and reconstituted with the mobile phase and injected into the HPLC. Separation was accomplished using a reverse phase chromatography using C18 analytical column, and detection was afforded by monitoring the eluent at an ultraviolet wavelength of 326 nm. Standard curves were highly linear over the range 10 to 10000 ng/mL (r2 >0.99). Recovery ranged from 52-69% over a 40-fold range of plasma concentrations from 50 to 2000 ng/mL. Intra- and inter-day coefficient of variation and mean error in were less than 20% at plasma concentrations ranging from 10 to 1000 ng/mL. The utility of the assay was demonstrated in a pharmacokinetic evaluation of milrinone in two rats given intravenous bolus doses. The developed assay was sensitive, specific and appropriate for monitoring milrinone in rat or human plasma samples.