Quantitation of RU 486 in human plasma by HPLC and RIA after column chromatography

Chromosorb column chromatography was used for separation of RU 486 from its immunologically cross-reacting metabolites prior to quantitative analysis by radioimmunoassay (RIA) or high-performance-liquid chromatography (HPLC). The results of the two assay methods were in good agreement with each other (r = 0.99, n = 29). The retention time of RU 486 in our HPLC system was 2.5 min. Plasma concentrations of RU 486 were measured by HPLC up to 48 h following single oral administration of 100, 400, 600 and 800 mg of RU 486 to female volunteers. The plasma peak concentrations (2.0-2.5 micrograms/ml) were reached within the first hour. After redistribution, the plasma concentrations of RU 486 were not significantly affected by the doses studied but remained in the same range throughout the 48 hours. The plasma half-life between 24 and 48 hours was 27 hours or more. We conclude that HPLC is valuable in studies on the metabolism and pharmacokinetics of RU 486, but a less laborious RIA method after Chromosorb column chromatography is suitable and gives reliable results in large-scale clinical studies.