Safety, tolerance, and pharmacology of 9-beta-methylcarbacyclin calcium (ciprostene calcium) was investigated in healthy male volunteers. This stable prostacyclin analogue was infused intravenously into groups of 12, 11, and three volunteers for three, six, and eight hours, respectively, in doses up to 480 ng/kg/min. Based on the tolerance data obtained, a single-blind, placebo-controlled study was conducted. Seven subjects were infused for 8 hr/d for three days with ciprostene at a maximum dose of 160 ng/kg/min and seven subjects received placebo. One subject from each group did not complete the infusion schedule, and they were not included in the final analysis. During infusion of ciprostene, consistent changes in blood pressure and heart rate did not occur. Most frequent adverse drug reactions consisted of headache, restlessness, nausea, perspiration, flushing, and jaw pain. As compared with placebo, ADP-induced platelet aggregation was inhibited during the infusion period (P = .048). Significant (P = .04) elevations of platelet cyclic AMP were observed in subjects during infusion of ciprostene. Pre- versus postinfusion routine laboratory evaluations, fibrinogen concentration, antiplasmin activity, and plasminogen and template bleeding times remained unchanged. Placebo- and drug-treated subjects had a daily postinfusion shortening of euglobulin clot lysis time (ECLT). The preinfusion minus postinfusion ECLT for ciprostene subjects on days 2 and 3 (133 and 118 min, respectively) compared with placebo (239 and 217 min) suggest a trend to increased fibrinolytic activity. Based on the outcome of this trial, it is estimated that ciprostene is about 15 times less potent than prostacyclin.(ABSTRACT TRUNCATED AT 250 WORDS)