Thrombolytics / Fibrinolytics
Antiplatelets prevent clots from forming — thrombolytics destroy clots that already exist. The window to use them is brutally narrow, and the biggest risk is the very mechanism that makes them work.
Core Concept
Thrombolytics (fibrinolytics) such as alteplase (tPA), tenecteplase, and reteplase work by converting plasminogen to plasmin, which actively dissolves fibrin clots. They do not prevent new clots — they break down existing ones. This makes them emergency drugs for acute ST-elevation MI (STEMI), acute ischemic stroke, and massive pulmonary embolism. Timing is critical: for ischemic stroke, alteplase must be given within 3–4.5 hours of symptom onset; for STEMI, door-to-needle time is 30 minutes when expected door-to-balloon (PCI) time exceeds 120 minutes. Because plasmin breaks down fibrin systemically, the primary danger is hemorrhage — intracranial hemorrhage is the most lethal complication. Before administration, assess for absolute contraindications: active internal bleeding, recent (within 3 months) intracranial surgery or stroke, known intracranial neoplasm, and uncontrolled severe hypertension. During and after infusion, monitor neurological status every 15 minutes, watch all puncture sites for oozing, avoid invasive procedures (no IM injections, no arterial sticks, no foley placement unless essential), and keep aminocaproic acid available as the antidote for fibrinolytic-induced bleeding. Monitor aPTT, PT/INR, fibrinogen, and platelet count. Apply pressure for at least 20 minutes to any venipuncture site.
Watch Out For
Don't confuse thrombolytics (dissolve existing clots) with antiplatelets (prevent platelet aggregation in new clots) — they treat different phases. Students often think heparin is a thrombolytic; heparin prevents clot extension but does not lyse clots. The stroke window is 3–4.5 hours from symptom onset, not from hospital arrival — "last known well" time drives eligibility.
Clinical Pearl
Think of tPA as a wrecking ball for clots — it can't aim. Every fibrin strand in the body is a target, so bleeding can happen anywhere. Aminocaproic acid is the emergency brake.
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