Thrombolytics and antiplatelet agents are two major groups of drugs used to manage blood clots. Thrombolytics help dissolve an already formed clot, while antiplatelet drugs prevent platelets from sticking together. Both classes play a major role in treating heart attacks, strokes, and other circulation-related conditions.
What Are Thrombolytics?
Thrombolytics, also called fibrinolytics, are medicines that break down dangerous blood clots. When the body detects an injury, it produces a natural substance called tissue plasminogen activator (tPA), which helps dissolve clots. Thrombolytic drugs mimic or enhance this natural process.
How Thrombolytics Work
- They convert plasminogen (inactive form) into plasmin (active enzyme).
- Plasmin breaks down fibrin, the main structure that forms a clot.
- This action helps dissolve the clot and restores blood flow.
Common Thrombolytic Drugs
- Streptokinase
- Urokinase
- Alteplase (rt-PA)
- Reteplase
- Tenecteplase
Individual Drug Highlights
Streptokinase
- Derived from streptococci bacteria.
- Forms a complex with plasminogen to produce plasmin.
- Can cause allergic reactions because it is a foreign protein.
- Used for heart attack, DVT, and pulmonary embolism.
Urokinase
- Originally isolated from human urine (now produced from kidney cells).
- Direct activator of plasminogen.
- Non-allergenic and safer to use after previous streptokinase exposure.
Alteplase (rt-PA)
- Recombinant form of natural t-PA.
- Selective for fibrin-bound plasminogen.
- Short half-life and highly effective for dissolving fresh clots.
Reteplase & Tenecteplase
- Modified versions of alteplase.
- Longer half-life, allowing easier dosing.
- Tenecteplase requires only a single IV bolus.
Uses of Thrombolytics
- Acute myocardial infarction (heart attack) – best when given within the first hour.
- Deep vein thrombosis (DVT)
- Pulmonary embolism
- Sometimes used in selected cases of stroke (specific guidelines apply).
Contraindications
Thrombolytics should not be given in conditions with high bleeding risk:
- Recent surgery, trauma, or childbirth
- Uncontrolled high blood pressure
- Recent stroke
- Peptic ulcer
- Severe liver disease
- Any active bleeding disorder
Antifibrinolytics
These drugs work opposite to thrombolytics. Instead of dissolving clots, they prevent the breakdown of clots. They are used when there is too much bleeding.
Common Antifibrinolytics
- Epsilon-Amino Caproic Acid (EACA)
- Tranexamic Acid
They are used to control bleeding after dental procedures (especially in hemophilia), excessive menstrual bleeding, and bleeding caused by fibrinolytic overdose.
What Are Antiplatelet Agents?
Antiplatelet drugs stop platelets from clumping together. When platelets stick to each other, they form the initial plug of a clot. These drugs are very important in preventing heart attacks and strokes, especially in people with narrowed arteries.
Types of Antiplatelet Drugs
- Aspirin – blocks thromboxane A2, a chemical that promotes platelet aggregation.
- Dipyridamole – increases cAMP inside platelets and reduces their activity.
- P2Y12 Inhibitors – such as clopidogrel, prasugrel, ticagrelor; block ADP receptors on platelets.
- Glycoprotein IIb/IIIa inhibitors – used in high-risk cardiac procedures.
How Antiplatelet Drugs Work
Each drug class targets a different pathway involved in platelet activation:
- Aspirin stops platelet production of thromboxane, a strong clot promoter.
- P2Y12 inhibitors block the ADP pathway needed for platelet activation.
- GP IIb/IIIa inhibitors block the final step of platelet aggregation.
Uses of Antiplatelet Agents
- Prevention of heart attack and stroke
- After stent placement
- In patients with angina
- Peripheral vascular disease
- As part of dual antiplatelet therapy after cardiac interventions
Side Effects of Antiplatelet Drugs
- Bleeding (most common)
- Stomach irritation (especially with aspirin)
- Allergic reactions
- Headache (dipyridamole)
Detailed Notes:
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