Competitive radio-ligand assay for danazol [17β-hydroxypregn-4-en-20-yno(2,3-d)isoxazole] by using pregnant-guinea-pig serum

Human plasma (50 μl) is mixed with H2O (0.5 ml), and the mixture is extracted with hexane (3 X 3 ml) and the dried extract is submitted to chromatography to separate the antifertility drug danazol from progesterone and other interfering compounds (including metabolites of danazol). The drug zones are extracted with ethanol, and the soln. so obtained is analyzed for danazol by a binding method involving use of [3H]progesterone-saturated protein from guinea-pig plasma. The bound and free steroids are separated with use of charcoal, and the supernatant soln. is counted for 3H. Recovery is approximately equal to 58 percent, and the calibration graph is rectilinear for up to 12 ng of danazol. Attention is drawn to the fact that the binding system used has hitherto been considered virtually specific for progesterone. (U.S.)