The effects of nifedipine, a calcium antagonist, on platelet function.

Platelet function was studied before and 1 hour after ingestion of 20 mg nifedipine, a new calcium antagonist, in 20 patients with coronary heart disease. Platelet counts remained unchanged. Platelet adhesiveness, measured as retention in glass bead columns with Hellem's method for native blood, did not drop significantly eigher when 0.9 or 3.6 ml of blood was used. Platelet aggregation, which is dependent on extracellular calcium, was induced in citrated platelet-rich plasma. The mean maximal rate of primary aggregation, initiated with three different concentrations of adenosine diphosphate, was reduced by 20% to 26%. The rate of irreversible collagen-induced aggregation was on average 23% lower after nifedipine. The mean bleeding time was 36 seconds, or 12%, longer after ingestion of the drug. The moderate, but significant reduction of platelet aggregation and prolongation of the bleeding time by nifedipine may be mediated through inhibition of calcium transport across the platelet membrane.