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 and strokes.
Conditions Treated with Warfarin
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)
- 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, and 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 and causing excessive bleeding. This balance requires careful monitoring of the patient’s PT (prothrombin time) and INR (international normalized ratio).
Monitoring Warfarin Therapy
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 and 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 and INR should be assessed daily until a stable daily dose is reached (the dose that maintains PT and INR within therapeutic ranges and does not cause bleeding). From then on, PT and INR are checked every 2-4 weeks as long as drug therapy is continued.
Adverse Effects
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 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
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), and ‘purple toes syndrome’ (toes are painful and 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).
Risk Factors for Bleeding
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
- Hypertension
- Cerebrovascular disease
- Serious heart disease
- Anemia
- Malignancy
- Trauma
- 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
- Alcoholism
- History of GI ulcerations
- Drainage tubes (NG tube or urinary catheter)
- Occupations with high risks of traumatic injury
Drug Interactions
There are several drugs that can increase the effects of warfarin:
- Analgesics (Tylenol, aspirin, NSAIDs)
- Androgens and anabolic steroids
- Antibacterial drugs
- Antifungal drugs
- Antiseizure drugs
- Cardiovascular drugs
- GI drugs
- Thyroid medications
There are other that decrease the effects of warfarin, including:
- Antacids
- Diuretics
- 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 and 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 and dietary supplements as they can also have a profound effect on warfarin.
Vit. K is in most multivitamin supplements and 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:
- Alfalfa
- Celery
- Clove
- Feverfew
- Garlic
- Ginger
- Ginkgo
- Ginseng
- Licorice
Dietary Considerations
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
- Broccoli
- Brussel sprouts
- Soy beans
- Avocados
- Asparagus
- Dill pickles
- Green peas
- Green tea
- Canola, olive, and soybean oil
- Margarine and mayonnaise
Maintain a consistent level of consumption and 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: Patient Safety and Education
The goal is to implement safety measures to prevent trauma and bleeding. The following are important in the inpatient setting:
- Keep the call light in reach and assist with ambulation to prevent falling
- Provide an electric razor for shaving
- Avoid IM injections, venipunctures, and 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 and 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.
