Warfarin – Uses and Side Effects

Warfarin – Uses and Side Effects Video


Coumadin (or warfarin) is the most commonly used oral anticoagulant drug, often called a blood thinner. It is used to prevent blood clots in veins or arteries, reducing the risk of heart attacks & strokes.

Coumadin is given for long-term prevention or management of:

– Venous thrombosis (blood clot in a vein), including DVT
– Pulmonary embolism (blockage of an artery in the lungs), or
– Embolisms associated with atrial fibrillation or prosthetic heart valves.
– After a heart attack, Coumadin is given to reduce the risk of a recurring heart attack, stroke, & death.

Coumadin does not have a direct effect on an established thrombus (blood clot), but once a thrombus has occurred, the goal is to prevent secondary complications that may result.

Several proteins called coagulation factors are involved in the process that the body uses to form blood clots to help stop bleeding. When an injury occurs and bleeding begins, coagulation factors are activated in a sequence of steps (coagulation cascade) that eventually help to form a clot.

The goal of warfarin therapy is to maintain a balance between preventing clots & causing excessive bleeding. This balance requires careful monitoring of the patient’s PT (prothrombin time) and INR (international normalized ratio).

The PT measures the number of seconds it takes blood plasma to clot. It is usually performed with a partial thromboplastin time (PTT) and together they assess the amount & function of coagulation factors.

The INR is a calculation based on results of the PT and is used to monitor patients on warfarin therapy. The normal therapy range is 2-3, with a high INR indicating a higher risk of bleeding, and a low INR suggesting a higher risk of developing a clot. The INR can be used to adjust the patient’s drug dosage to get the PT into the desired range.

When starting warfarin, PT & INR should be assessed daily until a stable daily dose is reached (the dose that maintains PT & INR within therapeutic ranges & does not cause bleeding). From then on, PT & INR are checked every 2-4 weeks as long as drug therapy is continued.

The most common ADVERSE EFFECT of Coumadin is bleeding, which can occur anywhere in the body, spontaneously or in response to minor trauma.

Bleeding complications may present as severe bleeding, including heavier than normal menstrual bleeding, bruising (often not sure how it happened), blood in urine (red/brown in color), blood in stool (black/bloody), vomiting blood (sometimes looks like coffee grounds), bloody nose or gums (seen when brushing teeth), severe headache, pain in chest, abdomen, joint, muscle or other area, dizziness or weakness, hypotension, unexplained swelling, shortness of breath, or unexplained shock. Bleeding sites may also involve surgical wounds, skin lesions, or injection sites. The most tragic bleeding involves the brain and spinal cord.


Bleeding – most common

   Severe bleeding, including heavier than normal
menstrual bleeding.
Bruising (often not sure how it happened).
Blood in urine (red/brown in color).
Blood in stool (black/bloody).
Vomiting blood (sometimes looks like coffee grounds).
Bloody nose or gums (seen when brushing teeth).
Severe headache or pain in chest,abdomen, joint, muscle,
or other area.
Dizziness or weakness, hypotension.
Unexplained swelling, shortness of breath, or unexplained shock
Bleeding sites may also involve surgical wounds, skin lesions,
or injection sites.
Most tragic bleeding involves the brain and spinal cord.

Some less common ADVERSE EFFECTS…

Several studies have shown a decrease in bone mineral density, leading to osteoporosis – thought to be linked to the reduced intake of vitamin K, which is necessary for bone health.

Side effects involving the skin include dermatitis, alopecia (hair loss), & ‘purple toes syndrome’ (toes are painful & look purple or dark). Warfarin-induced skin necrosis is a rare but serious complication, usually occurring when warfarin treatment is initiated in a patient with protein C deficiency (which is a naturally occurring anticoagulant).

Warfarin can cause major or fatal bleeding – which is more likely to occur when the medication is first started or if too much warfarin is taken.

Risk factors for bleeding include:

    Age 65 years or older
Highly variable INRs
History of GI bleeding
Cerebrovascular disease
Serious heart disease
Renal insufficiency
Similar drug taken at the same time
Long duration of warfarin therapy

Warfarin should NOT be given to patients with:

    GI ulcerations
Blood disorders associated with bleeding
Severe kidney or liver disease
Severe hypertension
Recent surgery of the eye, spinal cord or brain
During pregnancy

It should be used cautiously in patients with:

    Mild hypertension
Renal or hepatic disease
History of GI ulcerations
Drainage tubes (NG tube or urinary catheter)
Occupations with high risks of traumatic injury

There are several drugs that INCREASE the effects of warfarin:

    Analgesics (Tylenol, aspirin, NSAIDs)
Androgens & anabolic steroids
Antibacterial drugs
Antifungal drugs
Antiseizure drugs
Cardiovascular drugs
GI drugs
Thyroid medications

There are other drugs that DECREASE the effects of warfarin, including:

Estrogens, including oral contraceptives
Vitamin K (which is the antidote for warfarin overdose)

*Alcohol may INCREASE or DECREASE the effects of warfarin, depending on the state of the liver & the rate of metabolism.

Therefore, it is extremely important for the healthcare provider giving warfarin to be aware of all medications the patient is taking, as well as herbal & dietary supplements as they can also have a profound effect on warfarin.

– Vit. K is in most multivitamin supplements & should be taken consistently to avoid fluctuating vitamin K levels.
– Vit. C in excess of 500 mg per day may lower INR
– Vit. E in excess of 400 IU per day may increase warfarin effects

Herbs that may increase effects of warfarin include:


Diet and Coumadin.
Eating a normal, balanced diet is important for the patient taking Coumadin because changes in diet can interact with the Coumadin treatment. For example, too much vitamin K can lower the effect of Coumadin since vitamin K is involved in the body’s clotting process. There is no need to avoid foods with vitamin K, but it is best to maintain a consistent level of consumption of the products and to be aware of foods with vitamin K so over-consumption does not occur.

Foods rich in vitamin K include:

    Green leafy vegetables
Beef liver
Brussel sprouts
Soy beans
Dill pickles
Green peas
Green tea
Canola, olive, & soybean oil
Margarine & mayonnaise

Maintain a consistent level of consumption & avoid over-consumption. Too much vitamin K can lower the effect of Coumadin since vitamin K is involved in the body’s clotting process.

Nursing tips when caring for the patient on Coumadin therapy:

The goal is to implement safety measures to prevent trauma & bleeding. The following are important in the inpatient setting.

– Keep the call light in reach & assist with ambulation to prevent falling
– Provide an electric razor for shaving
– Avoid IM injections, venipunctures, & arterial punctures when possible
– Avoid intubations when possible (NG tubes, urinary catheters)

The patient at home needs to be reminded to:

– Take Coumadin exactly as prescribed.
– If a dose is missed, take as soon as possible on the same day, but do not take a double dose the next day to make up for the missed dose.
– Have regular blood tests & visits with healthcare provider.
– Call healthcare provider right away if too much Coumadin is taken, if they are sick with diarrhea, infection, or fever; or if they have a fall or injury, especially if they hit their head.


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by Mometrix Test Preparation | This Page Last Updated: January 30, 2024