Fibrinolytic Drugs

Drugs that trigger conversion of plasminogen to plasmin can lyse established clots (Figure 1). They are used in acute myocardial infarction to re-establish coronary perfusion or to treat large pulmonary embolism. There may be a benefit for some stroke patients (Barber et al., 2006).

Streptokinase is a drug derived from beta-haemolytic streptococcal cultures. It induces the formation of antibodies that render streptokinase ineffective if readministered within 12 months and may cause allergic reactions (CSL Biotherpies, 2008). Alteplase and reteplase are derived from human tissue and do not induce antibodies. These drugs are more effective for clot bound plasminogen than streptokinase (Rang et al., 2012).
 
During treatment with fibrinolytic drugs, all clots in the body are lysed so caution is required with puncture sites etc. The antifibrinolytic drug tranexamic acid counteracts the effects of fibrinolytic drugs. It inhibits plasminogen activation and is used in the treatment of menorrhagia.

Laboratory Testing and Anticoagulant Therapy

Common laboratory tests are shown in Table 3. These are tests in vitro so may not reflect true haemostatic function in the body. INR and aPPT cannot measure clot stability, platelet function or fibrinolysis, all of which affect ability of the patient to maintain normal haemostasis (Hoffman & Monroe, 2007; Tanaka et al., 2009). Traditional tests of coagulation are not sensitive to factor Xa or direct thrombin inhibitors (Hoffman & Monroe, 2007). Thromboelastography (TEG) is used increasingly to measure the whole of haemostasis during major surgery (Adams, et al., 2007), providing more realistic evaluation of factor, platelet and fibrinolytic activity (Kroll. 2010).