High-performance liquid chromatographic determination of methylprednisolone and methylprednisolone 21-[8-[methyl-(2-sulfoethyl)amino]-8-oxoctanoate] sodium salt in human plasma.

A high-performance liquid chromatographic assay method with ultraviolet detection at 243 nm has been developed for the quantitative determination of methylprednisolone (MP) and methylprednisolone 21-[8- [methyl-(2-sulfoethyl)amino]-8-oxoctanoate] sodium salt (MPSO) in human plasma. The method is simple, rapid and sensitive to detect MP and MPSO in human plasma following administration of therapeutic doses of MPSO. The assay procedure involved stabilization of plasma samples by addition of disodium ethylenediaminetetraacetic acid and ion-pair extractions of MPSO with tetraethylammonium chloride. After extracting both drugs and internal standard into chloroform, the extract was evaporated to dryness under nitrogen. The resulting residue was reconstituted in 200-500 microliter of mobile phase and chromatographed on a C18 IBM reversed-phase column (5 micron). The mobile phase was a mixture of water-actetonitrile-isopropanol (71:19.9:10) containing 50 microliter of 0.1 M hydrochloric acid and 0.497 g tetraethylammonium chloride. Propyl p-hydroxybenzoate was used as an internal standard. The chromatographic responses were linear up to about 200 micrograms/ml for MP and 80 micrograms/ml for MPSO in human plasma. The assay detection limit was approximately 7 ng/ml for MP and 25 ng/ml for MPSO in human plasma. Statistical analysis indicated an average recovery of 102.0 +/- 4.71% for MP and 75.2 +/- 2.88% for MPSO. Human plasma levels are reported for MP and MPSO following single-dose intravenous administration of 100-mg equivalents of MPSO.