BIOLOGICAL MONITORING OF 3 ANTITHROMBOTIC DRUGS - SINGLE-DOSE THERAPY

A randomised study using 40 New Zealand White male rabbits was perform ed to compare the effects of three antithrombotic drugs on eight clini cal haemostatic function tests. The animals were divided into four tre atment groups. The treatment groups were saline (control), unfractione d heparin (UFH), low-molecular-weight heparin (LMWH), and recombinant hirudin (r-hirudin). Blood samples were collected 2 and 12 h after adm inistration of the drugs. The following tests were performed: bleeding time (BT), platelet count, prothrombin time (PT), activated partial t hromboplastin time (APTT), thrombin time (TT), fibrinogen concentratio n (Fg), antithrombin III (ATIII), and antifactor Xa activity (antiXa a ctivity). Effects attributable to drug treatment for each analyte were determined by comparison with the control group. At 2 h after medicat ion, in the UFH treated group, TT was moderately prolonged (p<0.05) an d antiXa activity was significantly higher (p<0.05) than the respectiv e values of the control group. In the LMWH-treated group the antiXa ac tivity was significantly higher (p<0.01) than that of the control grou p. In the rr-hirudin-treated group, the APTT and TT were significantly prolonged (APTT, p<0.01; the TT samples did not clot) when compared t o the control group. However, 12 h after administration, no significan t differences (p>0.05) between groups were observed for any of the stu died analytes. It might be concluded that the antiXa assay has the pot ential of being a sensitive screen for heparin therapy and that the ab sence of changes in the bleeding time, antithrombin III, and antiXa as says - with a markedly prolonged thrombin time - indicates that, in vi vo, r-hirudin acts as a specific inhibitor of thrombin.