How Does the Blood Clot?
Updated December 15, 2014.
Heparin.
Heparin is an intravenous drug that has an immediate (within seconds) inhibitory effect on the thrombin system. Its dosage can be adjusted frequently, following the PTT blood test (the partial thromboplastin time) to achieve the desired effect.
Low molecular weight heparin: enoxaparin, dalteparin. LMWH is a ?purified? derivative of heparin. Its major advantages are that it can be given as a skin injection (which almost anyone can learn to do in a few minutes), and does not need to be closely monitored with blood tests. Thus, unlike heparin, LMWH can be administered safely on an outpatient basis.
Coumadin. Coumadin is an oral anti-thrombin drug that can be taken chronically. The dose must be carefully monitored by following the prothrombin time (PT), a blood test.
Drugs that ?dissolve? fibrin ? the fibrinolytic drugs. These powerful drugs actually dissolve fibrin strands that have already formed.
TPA, streptokinase, urokinase. These are the intravenous drugs that are administered acutely during the first few hours of an acute heart attack or stroke, to attempt to re-open an occluded artery, and prevent permanent tissue damage.
Aspirin and diypyramidole. These drugs have a modest effect on platelet ?stickiness,? but have few important side effects.
Ticlopidine (Ticlid) and clopidrogel (Plavix). These drugs are somewhat more powerful than the first group, but can be poorly tolerated and can have important side effects. They are generally used in patients who need, but cannot tolerate, aspirin.
IIb/IIIa inhibitors: abciximab (Reopro), eptifabitide (Integrilin), tirofiban (Aggrastat). The IIb/IIIa inhibitors are the most powerful group of platelet inhibitors. They inhibit a receptor on the surface of platelets (the so-called IIb/IIIa receptor) that is essential for platelet stickiness. Their chief usage is to prevent acute clotting after interventional procedures (such as angioplasty and stent placement), and in patients with acute coronary artery syndromes, such as unstable angina. These drugs are very expensive and (in general) must be given intravenously.
How can abnormal blood clotting be treated?
Drugs used for preventing or treating abnormal blood clotting can be aimed either at the platelets, or at the thrombin system. While they all have their own profile of side effects, one side effect common to all these drugs is excess bleeding. They must all be used with appropriate precautions.Drugs aimed at the thrombin system.
Drugs that prevent further fibrin from forming. These drugs, which inhibit one or more of the proteins involved in the thrombin clotting system, are used for both arterial and venous clotting problems.Heparin.
Heparin is an intravenous drug that has an immediate (within seconds) inhibitory effect on the thrombin system. Its dosage can be adjusted frequently, following the PTT blood test (the partial thromboplastin time) to achieve the desired effect.
Low molecular weight heparin: enoxaparin, dalteparin. LMWH is a ?purified? derivative of heparin. Its major advantages are that it can be given as a skin injection (which almost anyone can learn to do in a few minutes), and does not need to be closely monitored with blood tests. Thus, unlike heparin, LMWH can be administered safely on an outpatient basis.
Coumadin. Coumadin is an oral anti-thrombin drug that can be taken chronically. The dose must be carefully monitored by following the prothrombin time (PT), a blood test.
Drugs that ?dissolve? fibrin ? the fibrinolytic drugs. These powerful drugs actually dissolve fibrin strands that have already formed.
TPA, streptokinase, urokinase. These are the intravenous drugs that are administered acutely during the first few hours of an acute heart attack or stroke, to attempt to re-open an occluded artery, and prevent permanent tissue damage.
Drugs aimed at platelets.
These three groups of drugs, in one way or another, reduce the ?stickiness? of platelets. They are used most commonly in preventing arterial clots from forming.Aspirin and diypyramidole. These drugs have a modest effect on platelet ?stickiness,? but have few important side effects.
Ticlopidine (Ticlid) and clopidrogel (Plavix). These drugs are somewhat more powerful than the first group, but can be poorly tolerated and can have important side effects. They are generally used in patients who need, but cannot tolerate, aspirin.
IIb/IIIa inhibitors: abciximab (Reopro), eptifabitide (Integrilin), tirofiban (Aggrastat). The IIb/IIIa inhibitors are the most powerful group of platelet inhibitors. They inhibit a receptor on the surface of platelets (the so-called IIb/IIIa receptor) that is essential for platelet stickiness. Their chief usage is to prevent acute clotting after interventional procedures (such as angioplasty and stent placement), and in patients with acute coronary artery syndromes, such as unstable angina. These drugs are very expensive and (in general) must be given intravenously.
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