[Effects of cimetidine and ranitidine on blood coagulation].

The influence of cimetidine and ranitidine on blood coagulation and plasmatic fibrinolysis were assessed in vitro and in vivo. After an intravenous bolus of 200 mg cimetidine a marked prolongation of plasmatic thrombin time was observed, which however did not occur after 50 mg of ranitidine. In vitro addition of cimetidine (0.12 mg/ml) and ranitidine (0.06 mg/ml) again led to prolongation of plasmatic thrombin time only after cimetidine, reaching double the initial value. This requires application of cimetidine in acute intestinal haemorrhage not as a bolus, but only by drip infusion. Continuous application of 600 mg over 12 hours did not result in changes of coagulation values. In contrast, ranitidine may be administered as a bolus. Bolus injections of 50 to 100 mg did not result in any prolongation of plasmatic thrombin time. The antifibrinolytic effect of both H2-receptor antagonists was investigated in the streptokinase-induced fibrinolysis spindle of the thrombelastogram. Clear-cut antifibrinolytic properties were not demonstrable for either preparation with this method.