Radioimmunoassay for sulprostone

The development of a radioimmunoassay for measuring subnanogram amounts of the prostaglandin uterine stimulant, sulprostone (N-methanesulfonyl 16-phenoxy-ω-tetranor PGE 2 carboxamide), is described. The 9-carboxymethoxime derivative of sulprostone was coupled to keyhole limpet hemocyanin to prepare the immunogen, and to tyramine to yield a precursor suitable for radioiodination. The antiserum generated from rabbits was specific for sulprostone, showing cross reactivities of less than 0.1% against PGE 2, PGF 2α, and known sulprostone metabolites. The range for routine assay of sulprostone was 10–300 pg which corresponded to 50–1500 pg/ml of plasma. The coefficient of variation for replicate analyses on the same sample was 8–12%. The assay was used to measure the plasma levels of sulprostone in patients who had received the drug intramuscularly.