is a substance that prevents coagulation
; that is, it stops blood
from clotting. A group of pharmaceuticals called anticoagulants can be used in vivo
as a medication for thrombotic
disorders. Some chemical compounds are used in medical equipment, such as test tubes
, blood transfusion
bags, and renal dialysis
Anticoagulants are given to people to stop thrombosis
(blood clotting inappropriately in the blood vessels). This is useful in primary and secondary prevention of deep vein thrombosis
, pulmonary embolism
, myocardial infarctions
in those who are predisposed.
Vitamin K antagonists
The oral anticoagulants are a class of pharmaceuticals
that act by antagonizing the effects of vitamin K
. Examples include warfarin
. It is important to note that they take at least 48 to 72 hours for the anticoagulant effect to develop fully. In cases when any immediate effect is required, heparin
must be given concomitantly. Generally, these anticoagulants are used to treat patients with deep-vein thrombosis
(DVT), pulmonary embolism
(PE), 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.)
Heparin and derivative substances
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. Vacutainer brand test tubes containing heparin are usually colored green.
Low molecular weight heparin
Low molecular weight heparin
is a more highly processed product that 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.
Major pharmaceutical Heparin recall due to contamination
In March 2008 major recalls of Heparin were announced by pharmaceuticals due to a suspected and unknown contamination of the raw Heparin stock imported from China . The U.S. Food and Drug Administration was quoted as stating that at least 19 deaths were believed linked to a raw Heparin ingredient imported from the People's Republic of China, and that they had also received 785 reports of serious injuries associated with the drug’s use. According to the New York Times: 'Problems with heparin reported to the agency include difficulty breathing, nausea, vomiting, excessive sweating and rapidly falling blood pressure that in some cases led to life-threatening shock'.
Direct thrombin inhibitors
Another type of anticoagulant is the direct thrombin inhibitor
. Current members of this class include 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.
Anticoagulants outside the body
instruments, test tubes, blood transfusion bags, and medical and surgical equipment will get clogged up and become nonoperational if blood is allowed to clot. Chemicals can be 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 is denoted by mauve or purple caps on Vacutainer brand test tubes. This chemical strongly and irreversibly binds calcium. It is in a powdered form.
- Citrate is usually in blue Vacutainer tube. It is in liquid form in the tube and is used for coagulation tests, as well as in blood transfusion bags. It gets rid of the calcium, but not as strongly as EDTA. Correct proportion of this anticoagulant to blood is crucial because of the dilution. It can be in the form of sodium citrate or ACD.
- Oxalate has a mechanism similar to that of citrate. It is the anticoagulant used in fluoride (grey top) tubes.
For the meaning of more colors, see Vacutainer#including coagulants.