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Pharmacokinetics of a New Thromboxane A2 Receptor Antagonist, S‐1452, and its Effect on Platelet Aggregation in Healthy Volunteers

To study the pharmacokinetics of a new thromboxane A2 (TXA2) receptor antagonist, S‐1452, eight healthy volunteers were given placebo or S‐1452 orally on four occasions in step‐wise increasing doses of 10 mg, 25 mg, and 50 mg separated by 2‐week intervals. Blood samples for measurement of plasma concentrations of the drug and of its inhibitory effect on platelet aggregation were obtained for 24 hours after administration. Bleeding time after administration was measured. S‐1452 was rapidly absorbed, with a peak plasma concentration at 30 minutes after administration. Thereafter, the drug was rapidly eliminated (elimination half‐life, 0.4–0.5 hours), and no drug was detected at 6 hours. The inhibitory effect of S‐1452 on platelet aggregation, which was stimulated by the TXA2 receptor agonist U‐46619, persisted more than 6 hours after drug administration. Bleeding time was slightly prolonged after a single dose of S‐1452. These results suggest that although S‐1452 is rapidly eliminated in plasma, its inhibitory effects on platelet aggregation persist for a longer period. Careful observations are needed to prevent potential bleeding episodes during repeated treatment with the drug.