The effect of histamine (H2) receptor antagonists on the fibrinolytic activity in vitro

The effect of cimetidine and ranitidine on the fibrinolytic activity in vitro was tested. The inhibition rate of spontaneous lysis rose proportionally to the increasing drug doses. However, a similar effect was obtained with two other drugs of different chemical structures and pharmacological properties. Streptokinase activated fibrinolyse was not affected by either of the drugs at any concentration. Nor was clot formation affected in these experiment conditions. The results of the tests in vitro indicate that inhibition of euglobulin fibrinolysis by H2-receptor antagonists is not specific for these drugs and not connected with their pharmacological properties. It is possible to assume that, during therapeutic use, cimetidine and ranitidine have no antifibrinolytic effect. Possible explanation and relevance of these observations are discussed.