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Hypertension & Stroke



Brand Names: Coumadin, Panwarfin
Drug Class: Anticoagulant
Available in: Tablets, injection
Available Without a Prescription? No
Available as a Generic? Yes

Side Effects

Serious: Allergic reaction (wheezing, breathing difficulty, hives, or swelling of lips, tongue, and throat); bleeding into skin and soft tissue; abnormal bleeding from nose, gastrointestinal tract, urinary tract, or uterus; severe infection; excessive or unexpected menstrual bleeding; black vomit; bruises or purple marks on skin. Consult your doctor immediately if you experience any of these side effects.

Common: No common side effects have been reported.

Less Common: Loss of appetite, unusual weight loss, nausea, vomiting, skin rash, diarrhea, cramping.

Principal Uses

To prevent blood clot formation in people suffering from heart, lung, and blood vessel disorders that could lead to heart attack, stroke, or other problems.

How the Drug Works

Warfarin blocks the action of vitamin K, a compound necessary for blood clotting.


Adults: To start, 10 to 15 mg daily, taken once a day. Long-term, usually 2 to 10 mg per day, taken once a day. Children: The dose must be determined by a pediatrician. It should be taken at the same time every day.

Onset of Effect

36 to 48 hours.

Duration of Action

24 to 96 hours.

Dietary Advice

Warfarin can be taken with liquid or food.


Store in a tightly sealed container away from heat and direct light.

If You Miss a Dose

If you miss a dose, take it as soon as you remember, unless it is almost time for the next dose. In that case, skip the missed dose and go back to your regular schedule. Do not double the next dose.

Stopping the Drug

Take it as prescribed for the full treatment period, even if you begin to feel better before the scheduled end of therapy. The decision to stop taking the drug should be made by your doctor.

Prolonged Use

Regular tests of prothrombin time (a simple test that measures the time it takes for one stage of blood coagulation to occur) are needed when taking this drug. Your doctor may also take stool and urine samples periodically to check for the presence of blood.


Over 60: Adverse reactions may be more likely and more severe in older patients.

Driving and Hazardous Work: Avoid if you have blurred vision or feel dizzy. Avoid activities that could cause injury.

Alcohol: Use with caution. Alcohol can increase or decrease the effect of warfarin. Usually, consume no more than one drink a day.

Pregnancy: Warfarin may cause birth defects. Do not use during pregnancy.

Breast Feeding: Warfarin passes into breast milk. Do not use while nursing.

Infants and Children: Not recommended for children under 18.


Symptoms: Bleeding gums, uncontrolled nosebleeds, blood in the urine
or stools.

What to Do: Discontinue the medication and call your doctor, emergency medical services (EMS), or the nearest poison control center right away.

Drug Interactions

Consult your doctor for specific advice if you are taking steroid drugs, acetaminophen, allopurinol, aminogluthemide, antibiotics, antiarrhythmic heart drugs, androgens, antacids, antifungal drugs, antihistamines, aspirin, antidiabetic drugs, disulfiram, a non-steroidal anti-inflammatory drug (NSAID), barbiturates, benzodiazepine tranquilizers, calcium supplements, chloramphenicol, or any cholesterol-lowering drugs.

Food Interactions

Avoid green, leafy vegetables and other foods that are rich in vitamin K (liver, broccoli, cauliflower, kale, spinach, and cabbage). Intake of too much vitamin K can override the anticlotting effect of warfarin and render the drug useless. Conversely, certain substances can interfere with the absorption of vitamin K so much that normal, healthy clotting (necessary for wounds to heal) is impaired. Megadoses of vitamin E can do this, as can fish oil supplements and foods high in omega-3 fatty acids. These substances can enhance the effect of anticlotting drugs so much that a tendency to hemorrhage may result.

Disease Interactions

Consult your doctor about taking warfarin if you have high blood pressure, diabetes, serious liver or kidney disease, or a severe allergy.



From The Johns Hopkins Consumer Guide to Drugs. You can order this book now on our secure server.


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Hypertension & Stroke

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