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ANTIPLATELET DRUGS: SLOWLY FINDING THEIR NICHE?

Successes and failures in arterial thrombosis with aspirin, dipyridamole and sulphinpyrazone Antiplatelet drugs are occupying an increasing place among the anticoagulants. Aspirin, probably through prostaglandin inhibition, prevents platelet.adhesion and the release of adenosine diphosphate (ADP) and thromboxane A2 which precipitate aggregation. Unlike any other such agent, the effect is permanent for the life of the platelet (about 10 days). Sulphinpyrazone reverses decreased platelet survival and turnover, seemingly also by prostaglandin inhibition. Dipyridamole appears to inhibit ADP induced aggregation. The therapeutic value of these properties has been assessed in numerous clinical trials. In patients with prosthetic heart valves thrombotic complications may occur in 5-10 % of cases in the first year. Dipyridamole with anticoagulants seems more effective than anticoagulants alone, though there is no effect on mortality. Aspirin plus anticoagulants also gives more prot~ion than anticoagulants alone. Dipyridamole and sulphinpyrazone seem to be effective alone, but aspirin does not, thought it has enhanced the effect of dipyridamole. In cerebral vascular disease the risk of stroke is about 7 % per year after the frrst transient ischaemic attack. Sulphinpyrazone may reduce the number of attacks, and has been seen to reduce mortality in I trial. Aspirin has also reduced attacks in some trials (but not others) but has shown no effect on mortality. In 1 trial aspirin, alone or with sulphinpyrazone, was effective in reducing

attacks and mortality in men only, but sulphinpyrazone seemed no better than placebo.

Studies with aspirin in myocardial infarction look interesting but there is little conclusive evidence as yet. Patients with infarctions seem less likely to be regular aspirin users than those without and rheumatoid patients on aspirin seem to have very few infarctions at autopsy. Three large scale trials in progress at the moment may provide some more conclusive answers. Dipyridamole looks ineffective alone, but may potentiate the effects of aspirin. Several trials suggest that sulphinpyrazone reduces mortality, compared with placebo.

In peripheral vascular disease, none of these drugs have any established value, and the same seems to apply to complications of arterial catheterisation. However sulphinpyrazone appears to reduce occlusive events in AV shunts. Dipyridamole may modify vascular lesions associated with renal allograft rejection but some studies have shown little or no effect. It has also been seen, in controlled studies. to have a striking effect in malignant hypertension and proliferative glomerulonephritis, but aspirin has shown no benefit so far. Tsu, E.C. : American Journal of Hospital Pharmacy 35: 1507 (Dec 1978)

2 INPHARMA 17 Mar 1979 0156-2703/79/0317-0002 $00.50/ 0 © ADIS Press