Development and validation of a sensitive and specific radioimmunoassay for the determination of cicaprost in biological samples

Cicaprost is a potent, chemically and metabolically stable PGI2-mimetic. Pharmacodynamic effects were observed after oral administration of approximately 10 micrograms in man when plasma levels were in the low pg-range. The present report describes the development of a selective antiserum and a tracer with high specific activity and their use for the RIA determination of Cicaprost in biological samples. Cicaprost-[3H]-methylester with a specific activity of 819 GBq/mmol was used as a tracer. RIA-analyses were carried out with 0.05-0.5 ml plasma adjusted to pH 2 with 1 N HCl and extracted with 2.5 ml diethylether. Separation of antiserum bound and unbound Cicaprost was achieved by the charcoal method. Extraction recovery of Cicaprost was approximately 90% at pH approximately 2. The detection limit of the assay was 10-20 pg/ml plasma. Coefficients of variations were 6, 3 and 9% (within-day, n = 5) and 25, 12 and 10% (day-to-day, n = 11) at 50, 100 and 200 pg/ml. HPLC-chromatograms of plasma extracts did not reveal any peak apart from Cicaprost, demonstrating the specificity of the method. The present RIA for Cicaprost exhibits high specificity and sensitivity and will be used for further bioanalyses in pharmacokinetic study.