Effects of dipyridamole and acetylsalicylic acid on platelet functions in patients with aortic ball-valve prostheses.

The effects of dipyridamole and ASA on platelet functions were studied in patients with aortic ball-valve prostheses. Before ingestion, platelet adhesiveness was markedly reduced and platelet survival time slightly, but insignificantly shortened. ASA prolonged the bleeding time, reduced collagen-induced platelet aggregation, and inhibited secondary aggregation initiated by adrenalin. Similar effects were obtained with 2 Gm. of ASA alone as with 1 Gm. daily in combination with 225 mg. of dipyridamole. Platelet adhesiveness remained low. Depyridamole alone, 375 mg. daily, did not influence any of these parameters. The mean platelet half-life was prolonged from 3.52 to 3.72 days by each drug and to 4 days by the combined treatment. None of the differences was, however, statistically significant. A clinical study with ASA has been started in a larger series of patients to evaluate the effect on arterial thromboembolism.