QUANTITATIVE-ANALYSIS OF RETINOIDS IN BIOLOGICAL-FLUIDS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING COLUMN SWITCHING .3. DETERMINATION OF THE AROTINOID SUMAROTENE AND ITS Z-ISOMER IN HUMAN AND ANIMAL PLASMA

A fully automated and sensitive high-performance liquid chromatographic method, using on-line solid-phase extraction, automated column switching and ultraviolet detection, was developed for the third-generation retinoid (arotinoid) sumarotene {methyl p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)propenyl]phenyl sulphone; Ro 14-9706} and its Z-isomer. Nearly quantitative recoveries for human, rat and dog plasma were obtained by addition of acetonitrile (final content ca. 17%) to the plasma sample prior to injection. No isomerization was observed when the samples were stored in the autosampler for more than 20 h. The injection volume was 0.5 ml, resulting in quantification limits of 1 ng/ml for sumarotene and 2 ng/ml for the Z-isomer. More than 40 injections could be made on to one precolumn, allowing routine overnight injections. Using a 1-ml injection volume, the limit of quantification for sumarotene could be improved to 0.5 ng/ml. The method was applied to toxicokinetic studies in rats and dogs, and was used to monitor human plasma samples after repeated topical application. The method could also be adapted to etarotene (Ro 15-1570), which was used as an internal standard, and which is at present in clinical development.