Serum and urine kinetics of rosaprostol in volunteers

The kinetics of rosaprostol (9-hydroxy-19,20-bis-norprostanoic acid, Rosal) and of its metabolite (3-(2-n-hexyl-5-hydroxy-cyclopentyl)propionic acid) has been determined in plasma and in urine of 10 healthy volunteers after oral administration of 500 mg of rosaprostol. The peak of rosaprostol (of 524 ng/ml) appears at 4 h, whereas that of the metabolite (of 503 ng/ml) appears earlier (2 h); therefore the relationship between the two substances does not follow the precursor-successor relationship in plasma and a compartmental model has been used to fit the data. In this model the biotransformation process occurs before entering the central compartment (first-pass effect). The mean half-life of rosaprostol is equal to about 5 h and that of the metabolite is equal to 3 h. All of rosaprostol is biotransformed and only the metabolite is partially eliminated by the urine. The urinary excretion of the metabolite represents only a small fraction of the administered dose. The urinary clearance of the metabolite is equal to 5.3 l/h. The volume of distribution of both substances is equal to 21.2 l.