Thrombolytics are defined as substances that break down clots. “Thrombo-” is the prefix meaning clot, and “-lytic” is the suffix for breakdown or cell death. A thrombus is a blood clot in our circulatory systemand can cause a stroke and/or heart attack. The clot causes a blockage in the blood flow and whenever blood is prevented from getting to an area, you will have tissue ischemia (lack of oxygen), and if this continues cell/tissue death will occur. That is why it is very important to administer thrombolytics in urgent situations like stroke or heart attack as quickly as possible in the hope of reversing symptoms and preventing damage. Let’s go over some of the most commonly-used thrombolytics and see how they should be used.
First is Alteplase tissue-type plasminogen activator (t-PA). What is a plasminogen activator? Plasminogen is a protein in the blood that acts as a fibrinolytic or “clot buster” in that it breaks down already-formed clots. Fibrin is a substance in our bodies that responds to bleeding and helps form clots.
Alteplase is used to treat stroke, fatal heart attacks, pulmonary emboli (blood clots in the lungs), and when a central line catheter is being introduced into a blood vessel to prevent clots from forming around the catheter. Alteplase is given intravenously in one or two doses. The patient should be monitored very closely for signs of allergic reactions and bleeding. You should not administer Alteplase to a patient who has:
- active bleeding inside their body;
- a brain tumor or aneurysm (dilated blood vessel);
- a history of head injury or surgery on the brain or spinal cord within the past 3 months;
- severe or uncontrolled high blood pressure;
- a bleeding or blood clotting disorder such as hemophilia;
- bleeding inside their brain (if they are receiving alteplase to treat a stroke); or
- a recent history of stroke (if they are receiving alteplase for pulmonary embolism).
The dosage information for Alteplase differs based on what is being treated and also based on the weight of the patient. For example the usual adult dose for ischemic stroke is 0.9 mg/kg (up to 90 mg) IV over 60 minutes with 10% of the total dose administered as an initial IV bolus over the first minute.
Anistreplase is a thrombolytic complex of plasminogen and streptokinase used especially to treat heart attack and to lyse thrombi in coronary arteries, and has not been extensively studied for ischemic stroke. The usual adult dosage for myocardial infarction is 30 units IV once over 2 to 5 minutes. Patients treated within 1-3 hours of onset of symptoms receive the most benefit.
Reteplase is also a modified plasminogen activator. It contains less of the proteins of alteplase but is still an effective clot buster, used mostly in the treatment of heart attack. Reteplase is given intravenously, usually one dose. Side effects are similar to the other thrombolytics we have discussed so far: bleeding and allergic reaction. Reteplase is administered as a 10 + 10 unit double-bolus injection. Two 10 unit bolus injections are required for a complete treatment. Each bolus is administered as an intravenous injection over 2 minutes.
Streptokinase is a thrombolytic enzyme used to break down clots in heart attacks, pulmonary embolisms and some arterial clots. The myocardial infarction its most commonly used for is the ST elevation type. Streptokinase is produced by beta-hemolytic streptococci. By itself, it is not a plasminogen activator, but it binds with free circulating plasminogen to form a complex that can convert additional plasminogen to plasmin. Plasmin also breaks down fibrin clots. Studies using radioactive streptokinase have documented two disappearance rates: a “fast” half-life (18 minutes) and a “slow” half-life of 83 minutes. Because streptokinase is produced from streptococcal bacteria, it often causes febrile reactions and other allergic problems. It can also cause hypotension that appears to be dose-related. In heart attack: IV infusion: 1.5 million units administered IV within a 60 minute period. Intracoronary infusion: 20,000 units administered as an IV bolus, followed by a constant infusion of 2000 units/min for 60 minutes resulting in a total dose of 140,000 units. The greatest benefit in mortality reduction has been observed when streptokinase was administered within 1 hour after the onset of symptoms of heart attack, although statistically significant benefits were observed when administered up to 6 hours after, and some benefit was observed when administered up to 24 hours after initial onset of symptoms.
Tenectaplase is a thrombolytic that helps your body dissolve or break down clots; again mostly used during a heart attack of the STEMI type- ST elevated myocardial infarction. Tenectaplase is a modified tissue plasminogen activator that binds to fibrin and converts plasminogen to plasmin. Dosing increases from 30 to 40 to 50mg, until circulating fibrinogen is decreased. If possible before you administer tenecteplase, note if the patient has had a brain tumor or aneurysm, high blood pressure, hemophilia or other bleeding disorder, a history of stroke, or if they have recently had a head injury or surgery on their brain or spinal cord. Tenectaplase is administered intravenously with a side effect of bleeding which can be severe. The recommended total dose should not exceed 50 mg and is based upon patient weight. A single bolus dose should be administered over 5 seconds based on patient weight. Treatment should be initiated as soon as possible after the onset of heart attack symptoms.
To sum up thrombolytics, they are substances in a variety of formulations that work along with your own body’s defenses against breaking down clots. These interruptions in blood flow can be life threatening, and thrombolytics are most often used in urgent situations and time of onset of symptoms to treatment with a thrombolytic is crucial. Most of these drugs need to be given within a brief timeframe from onset of symptoms, intravenously by a health care professional and close monitoring of the patient needs to occur as these drugs come with potentially severe side effects like bleeding and allergic reactions. Careful attention needs to be given to patient’s’ medical history as there are also situations where these drugs cannot be administered. If patients have a history of bleeding, clotting, hypertension, active brain bleeds or aneurysms, these drugs are contraindicated.
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