Are agents affecting platelet functions clinically useful?

Abstract

Notwithstanding the large number of clinical trials, most of them designed and performed according to the requirements of modern clinical pharmacology, only a few firm clinical recommendations on drugs affecting platelet function in the prevention of arterial or venous thrombosis can be made at present. There is no good evidence for the clinical effectiveness of aspirin or any other drug affecting platelet function in patients with peripheral arterial occlusion or after vascular grafting. In cerebrovascular disease there is reasonable evidence that the administration of sulfinpyrazone can significantly reduce cerebral ischemia or mortality, but similar trials performed with aspirin, dipyridamole or clofibrate failed to reveal a significant difference in favor of the experimental treatment. Patients with angina only were shown to benefit from treatment with clofibrate, but prospective trials with dipyridamole or aspirin in the primary or secondary prevention of myocardial infarction did not reveal a significant reduction in morbidity or mortality in the experimental group. Use of a combination of the latter two drugs did, however, reveal a reduction in morbidity and mortality. In patients with prosthetic heart valves, there is firm evidence that dipyridamole and sulfinpyrazone therapy can normalize decreased platelet survival, an effect which has been shown to correlate well with the incidence of thromboembolism. Provided further trials lead to confirmatory conclusions, drugs inhibiting platelet function associated or not with oral anticoagulants may constitute an ideal prophylaxis in patients with a substitute valve. There is still much uncertainty as to whether dipyridamole, given in addition to conventional treatment, benefits patients with membranous or mesangiocapillary glomerulonephritis. The same holds for drugs inhibiting platelet function after kidney or heart transplantation in man. Only scanty reports are available on the usefulness of drugs affecting platelet function in thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome. Three different types of antiplatelet drugs are available for the prevention of postoperative deep vein thrombosis: dextran, oral drugs also affecting platelet function and heparin administered subcutaneously in small doses. In orthopedic surgery dextran 70 administered before and every second day after surgery was the drug showing the most convincing reduction in the incidence of phlebographically proved deep vein thrombosis. Major orthopedic surgery is precisely the type of surgery in which the effectiveness of small dose heparin is much in doubt and in which the effectiveness of aspirin and dipyridamole is still to be confirmed. In general surgery, use of a combination of 1 g aspirin and 0.225 g dipyridamole daily was shown to offer approximately the same level of protection as small doses of heparin, land these two forms of prevention seem to offer a greater degree of protection than dextran...