There are only two types of heparin. Heparin and low-molecular-weight heparin are the most commonly used anticoagulant medications that are not in pill form, according to the text "Williams Hematology." Physicians decide which type of heparin to use based upon effectiveness, safety, convenience and cost.
Heparin
Antithrombin III is a protein that breaks up substances that will form a clot. Heparin is an anticoagulant or a medication that prevents clots from forming. It attaches to antithrombin III and increases its ability to break up the clotting substances. With heparin attached to it, antithrombin III is 1,000 times more effective, according to the text "Basic & Clinical Pharmacology." Physicians closely monitor the clotting levels of all patients who receive heparin because the main negative effect is bleeding. In addition, 1 to 4 percent of people who take heparin for at least seven days develop heparin-induced thrombocytopenia, a condition in which platelet levels drop very low. Platelets are a type of blood cell involved in forming clots, so physicians also monitor the platelet levels.
Low-Molecular-Weight Heparins
Dalteparin, enoxaparin and tinzaparin are low-molecular-weight heparins. Pharmacists developed this type of heparin by decreasing the size of the heparin molecule. Heparin is measured by unified atomic mass units called daltons, or Da. The text "Williams Hematology" says that the average weight of a heparin molecule is 15,000 Da, while the low-molecular-weight heparin molecule averages between 4,000 to 5,000 Da. Thus, the low-molecular-weight heparins have this name because their heparin molecules weigh less.
Like heparin, they work by attaching to the antithrombin III protein. When heparin attaches to antithrombin III, the protein primarily interferes with the clotting factors thrombin, factor 9A and factor 10A. When a low-molecular-weight heparin attaches, antithrombin III increases its interference with factor 10A. Similar to heparin, the main negative effect is bleeding. Heparin-induced thrombocytopenia happens in just 0.3 to 0.45 percent, per "Williams Hematology."
Choosing Heparin
Physicians choose low-molecular-weight heparin for people who are having major orthopedic surgery because it stays in the bloodstream longer than heparin and lasts throughout the surgery.
In deep venous thrombosis, people develop blood clots in the large veins of their legs and the clots can travel to their lungs. Those with this disorder may use either type of heparin, but low-molecular-weight heparin is more convenient. Since it stays in the bloodstream longer, they need to take it only once or twice a day and can take it as an outpatient. People who take heparin must be a hospital patient.
Heparin is better for people with kidney problems. If the kidneys are not properly functioning, low-molecular-weight heparin will accumulate in the kidney and further damage it.
References
- "Basic & Clinical Pharmacology"; Bertram Katzung, M.D., Ph.D., Susan Masters, Ph.D., Anthony Trevor, Ph.D.; 2009
- "Williams Hematology"; Marshall Lichtman, M.D., Thomas Kipps, M.D. et al.; 2010
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