Anticoagulants (antithrombics, fibrinolytic, and thrombolytics) are a class of drugs that work to prevent the coagulation (clotting) of blood. Such substances occur naturally in leeches and blood-sucking insects. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis equipment.
- 1 Medications
- 1.1 Coumarins (vitamin K antagonists)
- 1.2 Heparin and derivative substances
- 1.3 Direct factor Xa inhibitors
- 1.4 Direct thrombin inhibitors
- 1.5 Antithrombin protein therapeutics
- 1.6 Other types of anticoagulants
- 2 Food and herbal supplements
- 3 General indications
- 4 Laboratory use
- 5 See also
- 6 References
- 7 External links
Coumarins (vitamin K antagonists)
These oral anticoagulants are derived from coumarin, which is found in many plants. A prominent member of this class is warfarin (Coumadin). It takes at least 48 to 72 hours for the anticoagulant effect to develop. Where an immediate effect is required, heparin must be given concomitantly. These anticoagulants are used to treat patients with deep-vein thrombosis (DVT), pulmonary embolism (PE) and to prevent emboli in patients with atrial fibrillation (AF), and mechanical prosthetic heart valves.
Patients aged 80 years or more may be especially susceptible to bleeding complications, with a rate of 13 bleeds per 100 person-years. These oral anticoagulants are used widely as poisons for mammalian pests, especially rodents. (For details, see rodenticide and warfarin.) Depletion of vitamin K by Coumadin therapy increases risk of arterial calcification and heart valve calcification, especially if too much vitamin D is present.
- Warfarin (Coumadin) is the main agent used in the US and UK.
- Acenocoumarol and phenprocoumon are used more commonly outside the US and the UK.
- Brodifacoum is used as rat poison, but is not used medically.
Heparin and derivative substances
Heparin is a biological substance, usually made from pig intestines. It works by activating antithrombin III, which blocks thrombin from clotting blood. Heparin can be used in vivo (by injection), and also in vitro to prevent blood or plasma clotting in or on medical devices. In venipuncture, Vacutainer brand blood collecting tubes containing heparin usually have a green cap.
Low molecular weight heparin
Low molecular weight heparin, a more highly processed product, is useful as it does not require monitoring of the APTT coagulation parameter (it has more predictable plasma levels) and has fewer side effects.
Synthetic pentasaccharide inhibitors of factor Xa
- Fondaparinux is a synthetic sugar composed of the five sugars (pentasaccharide) in heparin that bind to antithrombin. It is a smaller molecule than low molecular weight heparin.
Direct factor Xa inhibitors
Drugs such as rivaroxaban, apixaban and edoxaban work by inhibiting factor Xa directly (unlike the heparins and fondaparinux, which work via antithrombin activation). Also betrixaban (LY517717) from Portola Pharmaceuticals, darexaban (YM150) from Astellas and more recent TAK-442 letaxaban (Takeda) and eribaxaban (PD0348292) (Pfizer). The development of darexaban was discontinued in September 2011: in a trial for prevention of recurrences of myocardial infarction in top of dual antiplatelet therapy, the drug didn't work and the risk for bleeding was increased bij 300%. The development of letaxaban was discontinued for acute coronary syndrome in May 2011 following negative results from a Phase II study.
Direct thrombin inhibitors
Another type of anticoagulant is the direct thrombin inhibitor. Current members of this class include the bivalent drugs hirudin, lepirudin, and bivalirudin; and the monovalent drugs argatroban and dabigatran. An oral direct thrombin inhibitor, ximelagatran (Exanta) was denied approval by the Food and Drug Administration (FDA) in September 2004  and was pulled from the market entirely in February 2006 after reports of severe liver damage and heart attacks.  In November 2010, dabigatran was approved by the FDA to treat atrial fibrillation.
Antithrombin protein therapeutics
The antithrombin protein itself is used as a protein therapeutic that can be purified from human plasma or produced recombinantly (for example, Atryn, which is produced in the milk of genetically modified goats.)
Other types of anticoagulants
- Batroxobin, a toxin from a snake venom, clots platelet-rich plasma without affecting platelet functions (lyses fibrinogen).
- Hementin is an anticoagulant protease from the salivary glands of the giant Amazon leech, Haementeria ghilianii.
Food and herbal supplements
Foods and food supplements with blood-thinning effects include nattokinase, lumbrokinase, beer, bilberry, celery, cranberries, fish oil, garlic, ginger, ginkgo, ginseng, green tea, horse chestnut, licorice, niacin, onion, papaya, pomegranate, red clover, soybean, St. John’s wort, turmeric, wheatgrass, and willow bark. Many herbal supplements have blood-thinning properties, such as danshen and feverfew. Multivitamins that do not interact with clotting are available for patients on anticoagulants.
However, some foods and supplements encourage clotting. These include alfalfa, avocado, cat's claw, coenzyme Q10, and dark leafy greens such as spinach. Their intake should be avoided whilst taking anticoagulants or, if coagulability is being monitored, their intake should be kept approximately constant so that anticoagulant dosage can be maintained at a level high enough to counteract this effect without fluctuations in coagulability.
Grapefruit interferes with some anticoagulant drugs, increasing the amount of time it takes for them to be metabolized out of the body, and so should be eaten only with caution when on anticoagulant drugs.
|This section requires expansion. (December 2012)|
Therapeutic uses of anticoagulants include atrial fibrillation, pulmonary embolism, deep vein thrombosis, venous thromboembolism, congestive heart failure, stroke, myocardial infarction, and genetic or acquired hypercoagulability.
The decision to begin therapeutic anticoagulation often involves the use multiple bleeding risk predictable outcome tools clinicians use as non-invasive pre-test stratifications due to the potential for bleeds while on blood thinning agents. Among these tools are HAS-BLED, ATRIA, and CHA2DS2-VASc.
Laboratory instruments, blood transfusion bags, and medical and surgical equipment will get clogged up and become nonoperational if blood is allowed to clot. In addition, test tubes used for laboratory blood tests will have chemicals added to stop blood clotting. Apart from heparin, most of these chemicals work by binding calcium ions, preventing the coagulation proteins from using them.
- EDTA strongly and irreversibly binds calcium. It is in a powdered form. Full Form of EDTA is Ethylene Diamine Tetra Acetic Acid. It chelates calcium ion to prevent blood from clotting.
- Citrate is in liquid form in the tube and is used for coagulation tests, as well as in blood transfusion bags. It binds the calcium, but not as strongly as EDTA. Correct proportion of this anticoagulant to blood is crucial because of the dilution, and it can be reversed with the addition of calcium. It can be in the form of sodium citrate or acid-citrate-dextrose.
- Oxalate has a mechanism similar to that of citrate. It is the anticoagulant used in fluoride oxalate tubes used to determine glucose and lactate levels.
- Hylek EM, Evans-Molina C, Shea C, Henault LE, Regan S (2007). "Major hemorrhage and tolerability of warfarin in the first year of therapy among elderly patients with atrial fibrillation". Circulation 115 (21): 2689–96. doi:10.1161/CIRCULATIONAHA.106.653048. PMID 17515465.
- Adams J, Pepping J (1 Aug 2005). "Vitamin K in the treatment and prevention of osteoporosis and arterial calcification". American Journal of Health-System Pharmacy 62 (15): 1574–81. doi:10.2146/ajhp040357. PMID 16030366. Retrieved 2012-10-03.
- Ron Winslow; Avery Johnson (2007-12-10). "Race Is on for the Next Blood Thinner". Wall Street Journal. p. A12. Retrieved 2008-01-06. "...in a market now dominated by one of the oldest mainstay pills in medicine: the blood thinner warfarin. At least five next-generation blood thinners are in advanced testing to treat or prevent potentially debilitating or life-threatening blood clots in surgery and heart patients. First candidates could reach the market in 2009."
- Steg, PG; Mehta, SR; Jukema, JW; Lip, GY; Gibson, CM; Kovar, F; Kala, P; Garcia-Hernandez, A; Renfurm, RW; Granger, CB; Ruby-1, Investigators (2011). "RUBY-1: A randomized, double-blind, placebo-controlled trial of the safety and tolerability of the novel oral factor Xa inhibitor darexaban (YM150) following acute coronary syndrome". European heart journal 32 (20): 2541–54. doi:10.1093/eurheartj/ehr334. PMC 3295208. PMID 21878434.
- First Time European Approval for Xarelto in ACS http://decisionresources.com/The-Decision-Resources-Blog/May-2013/European-Approval-for-Xarelto-in-ACS-052913
- Di Nisio M, Middeldorp S, Büller HR (2005). "Direct thrombin inhibitors". N. Engl. J. Med. 353 (10): 1028–40. doi:10.1056/NEJMra044440. PMID 16148288.
- Thrombate III label
- FDA website for ATryn (BL 125284)
- Antithrombin (Recombinant) US Package Insert ATryn for Injection February 3, 2009
- Wittkowsky AK (September 2001). "Drug interactions update: drugs, herbs, and oral anticoagulation". J. Thromb. Thrombolysis 12 (1): 67–71. doi:10.1023/A:1012742628628. PMID 11711691.
- "HAS-BLED Score for Major Bleeding risk". MDCalc. Retrieved 2014-08-15.
- "ATRIA Bleeding Risk". MDCalc. Retrieved 2014-08-15.
- "CHA2DS2-VASc". MDCalc. Retrieved 2014-08-15.
- Staying Active and Healthy with Blood Thinners by the Agency for Healthcare Research and Quality