safety medical

Coumadin (Warfarin) Drug Interactions

Coumadin (warfarin) was first manufactured as a rodent pesticide. It is still actually produced on an industrial scale for this purpose today. However in the 1950's researchers discovered that in addition to getting rid of pesky rodents warfarin could be used in humans as a potent anticoagulant. The most well known branded version of warfarin is called Coumadin. Rather than functioning as an anticoagulant through reducing blood viscosity like an antiplatelet drug, Coumadin inhibits the ability of proteins and enzymes to form blood clots through its effects upon vitamin K which is essential to forming these proteins and enzymes. Though warfarin works very effectively as an anticoagulant its complex mechanism of action makes it interact with a broad spectrum of other drugs and substances.

Warfarin and antiplatelets

Warfarin should never be combined with antiplatelet drugs due to the severe side effects which can occur as a result of this combination. In some cases doctors may prescribe low doses of an antiplatelet medication to be taken along with Coumadin, but this is rare and the patient will usually be closely monitored. Combining warfarin with antiplatelet drugs significantly increases the risk of a hemorrhage occurring. The reason for this is that both warfarin and antiplatelets are anticoagulants but act in different ways. Coumadin works by reducing the ability to form clots while antiplatelets thin the blood. With these two actions combined the patient will have very thin blood that cannot clot. If the antiplatelet medication taken along with warfarin is of a high enough dosage internal bleeding can occur or even a brain hemorrhage. The most common antiplatelet taken accidentally while undergoing Coumadin treatment is aspirin. If you take aspirin while on Coumadin and experience any side effects such as changes in vision or blood in your stools and vomit a doctor should be contacted immediately so that you can be given vitamin K to increase your blood viscosity.

Warfarin and antibiotics

Different antibiotics can have different effects upon warfarin's ability to prevent blood clots. For this reason before starting any treatment of antibiotics if you are taking warfarin you should inform your doctor. Those on warfarin can still take antibiotics for treatment, but they must be much more closely monitored. Antibiotics which are azole antifungal agents increase Coumadin's effects. This results in an increased risk of bleeding. In extreme cases this can result in a brain hemorrhage or internal bleeding in the gastrointestinal system. With proper monitoring this can be avoided however. Other antibiotics such as rifampin have the opposite effect upon warfarin's effects. Rather than increasing warfarin's efficacy ridampin decreases it and puts the user at risk for developing a blood clot. The risk of this happening can also be minimized with close monitoring.

Warfarin and amiodarone (Cordarone)

Another medication that requires caution when coadministered with Coumadin is amiodarone. Amiodarone is a medication useful in controlling cardiac dysrhythmia. When combined together amiodarone and warfarin can lead to an increase in bleeding. This can lead to minor injuries causing massive losses of blood. It can also cause internal hemorrhaging in the gastrointestinal system as well as the brain. If closely monitored and with proper dose adjustment of each medication the risk can be minimized.

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