COMBINED HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND RADIOIMMUNOASSAY FOR A NOVEL RETINOBENZOIC ACID-DERIVATIVE, RAHYDRO-5,5,8,8-TETRAMETHYL-2-NAPHTHYL)-CARBAMOYL] BENZOIC-ACID (AM-80), IN HUMAN PLASMA

rahydro-5,5,8,8-tetramethyl-2-naphthyl)-carbamoyl] benzoic acid (Am-80 ) is a novel retinobenzoic acid derivative possessing retinoid activit y. Plasma concentration of this drug in clinical use is very low, less than 1 ng/ml, and could not be measured with direct immunoassays. A c ombination of high-performance liquid chromatography (HPLC) and radioi mmunoassay (RIA) was developed for this drug in human plasma. Am-80 in 0.5 ml of human plasma was extracted by solid-phase extraction, and t he extract was purified by reversed-phase HPLC. The immunoreactivity i n the fraction of the eluate was measured by competitive RIA. The with in- and between-assay variances were 4.1 to 15.5% and 4.1 to 7.0%, res pectively. The limit of quantification was 0.04 ng/ml in human plasma, which was much lower than that of direct RIA, 0.6 ng/ml previously re ported. This assay system could be used to observe the pharmacokinetic s of Am-80 in human even after dermal application at very low dose.