T-PA (Tissue Plasminogen Activator) is the Drug Used for Thrombolytic Therapy
The correct answer is D. T-PA (tissue plasminogen activator), which is the primary thrombolytic agent used to dissolve blood clots in acute thrombotic emergencies.
Why T-PA is the Thrombolytic Agent
T-PA is a serine protease that directly converts plasminogen to plasmin, the enzyme that dissolves fibrin clots 1. Unlike the other options listed, T-PA actively breaks down existing thrombi rather than preventing new clot formation 2.
Clinical Applications of T-PA
Acute Ischemic Stroke:
- IV recombinant t-PA (r-tPA) is recommended within 3 hours of symptom onset (Grade 1A evidence) 1, 3, 4
- Can be administered up to 4.5 hours from symptom onset with weaker evidence (Grade 2C) 1, 3
- Standard dosing is 0.9 mg/kg IV over 1 hour (maximum 90 mg) 4, 5
Coronary Artery Thrombosis:
- Used in Kawasaki disease patients with occlusive coronary thrombosis at 0.5 mg·kg⁻¹·h⁻¹ over 6 hours 1
- Alternative adult regimen is 0.2 mg/kg 1
Catheter-Directed Thrombolysis:
- Intraarterial r-tPA can be administered within 6 hours for patients ineligible for IV therapy (Grade 2C) 1
- Used for catheter occlusion in dialysis access 1
Why the Other Options Are NOT Thrombolytics
A. Heparin
- Mechanism: Anticoagulant that potentiates antithrombin to inhibit clotting factors (XIIa, XIa, Xa, IXa, IIa) 1
- Function: Prevents NEW clot formation but does NOT dissolve existing clots 1
B. Warfarin
- Mechanism: Inhibits vitamin K-dependent clotting factors (II, VII, IX, X) 1
- Function: Long-term anticoagulation for thromboprophylaxis, NOT thrombolysis 1
C. Aspirin
- Mechanism: Antiplatelet agent that inhibits cyclooxygenase pathway 1
- Function: Prevents platelet aggregation but does NOT lyse clots 1, 3
- Role in stroke: Recommended at 160-325 mg within 48 hours AFTER acute stroke, but only if thrombolysis is not given 1, 4, 5
Key Distinguishing Feature
T-PA is fibrin-specific and actively dissolves existing thrombi by converting plasminogen to plasmin at the clot site 1, 2, 6. The other agents either prevent clot formation (heparin, warfarin) or prevent platelet aggregation (aspirin), but none actively break down formed clots 1.
Other Thrombolytic Agents
While T-PA is the primary answer, other thrombolytic agents exist but are less commonly used 1:
- Urokinase (UK) - no longer manufactured 1
- Recombinant pro-urokinase (r-pro-UK) 1
- Streptokinase (SK) - not recommended for stroke 5
- Reteplase and tenecteplase (TNK) - newer agents 1
T-PA remains the only FDA-approved thrombolytic for acute ischemic stroke and is the gold standard for thrombolytic therapy 1, 7.