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Thrombolytic Drugs

Thrombolytic drugs are used to dissolve existing blood clots, which are gatherings or masses of blood. Blood clots that occur in cerebral, coronary or pulmonary vessels can be life-threatening, and thrombolytic drugs can safely and quickly treat these conditions.

Types of Thrombolytic Drugs

Thrombolytic drugs work by activating plasminogen, a substance found in the blood that produces a product called plasmin. Plasmin is an enzyme that can break down the bonds that hold blood clots together.

Thrombolytic drugs come in three types:

streptokinase (SK)
tissue plasminogen activator (TPA)
urokinase (UK).

Each of these drugs effectively breaks apart blood clots, but each works in a different way. Tissue plasminogen activators and streptokinase are the safest and most commonly used thrombolytic drugs. Urokinase thrombolytic drugs are more expensive and are used primarily in instances of pulmonary embolism.

Tissue plasminogen activators work in a four-step process:

First, the tPA binds to the fibrin,which holds the blood clot together, at the surface of the clot through an enzymatic process.
This activates the production of fibrin-bound plasminogen.
Plasmin is then produced from the plasminogen.
Plasmin then breaks down the fibrin molecules, dissolving the clot.

Streptokinase drugs are not enzymatic, but they do stimulate the production of plasminogen. These drugs differ from tPAs in that they do not target plasminogen on the clot specifically. This can lead to excessive bleeding.

Thrombus and Thrombolytic Drugs

Thrombolytic drugs need to be administered as soon after the indicating event as possible. In the event of a heart attack, thrombolytic drugs are most effective within the first three hours after the heart attack occurs.

Thrombolytic drugs can be administered in two ways. The most common method is through intravenous injection. This is the preferable treatment, as it may be quickly administered outside of the hospital for cases in which time is of the essence.

The other method of administration involves inserting a catheter with thrombolytic drugs at the tip directly into the blood vessels and releasing the drugs directly at the site of the clot.

Common Thrombolytic Drugs

Tissue plasminogen activators are used primarily in instances of:

heart attack
thrombotic stroks
pulmonary embolism.

The two most common brand names for this class of thrombolytic drugs are:

Activase®
Retavase®.

Streptokinase drugs are derived from the streptococci bacteria and are antigenic,meaning they activate a response from the immune system. They are used for:

arterial and venous thrombosis
heart attacks
pulmonary embolism.

The most commonly used brand name of this thrombolytic drug is Eminase®

Risks Associated with Thrombolytic Drugs

The use of thrombolytic drugs can lead to excessive bleeding at the site of the clot. In some instances, this can also lead to gastrointestinal and cerebral bleeding. In rare cases, hemorrhagic stroke can occur.

Thrombolytic drugs are often administered in conjunction with anticoagulants, drugs that prevent the blood from clotting, to help prevent recurrence of the blood clot at the site of the removed clot.

Resources

Klabunde, Richard E., Ph.D. (2007). Thrombolytic (Fibrinolytic) Drugs. Retrieved September 24, 2007, from the Cardiovascular Pharmacology Concepts Web site: http://www.cvpharmacology.com/thrombolytic/thrombolytic.htm.

University of Maryland Medical Center (n.d.). Heart attack and acute coronary syndrome. Retrieved September 24, 2007, from the University of Maryland Medical Center Web site: http://www.umm.edu/patiented/articles/thrombolytic_drugs

_used_restore_blood_flow_after_a_heart_attack_000012_7.htm.

VascularWeb (n.d.). Thrombolytic Therapy. Retrieved September 24, 2007, from the VascularWeb Web site: http://www.vascularweb.org/_CONTRIBUTION_PAGES/

Patient_Information/NorthPoint/Thrombolytic_Therapy.html.