Warfarin is used to prevent blood-clot formation by decreasing the production of blood-clotting substances by the liver.

Warfarin Facts
Brand names (manufacturers): Coumadin (Bristol-Myers Squibb); warfarin (various manufacturers)

Type of drug: Anticoagulant

Ingredient: Warfarin

Dosage form: Tablets (1 mg,
2 mg, 2.5 mg, 3 mg, 4 mg,
5 mg, 6 mg, 7.5 mg, and 10 mg)

Storage: Store warfarin at room temperature in a tightly closed, light-resistant container. Do not refrigerate.

Treatment

You can take warfarin with a full glass of water. In order to become accustomed to taking this medication, try to take it
at the same time each day.

If you miss a dose, take the missed dose as soon as possible. However, if it is almost time for the next dose, do not take the missed dose at all; just return to your regular dosing schedule. Do not double the next dose. If you miss more than two doses of warfarin in a row, contact your doctor as soon as possible.

Side Effects

Minor: Blurred vision, cramps, decreased appetite, diarrhea,
or nausea. These side effects should disappear as your body adjusts to the medication. Warfarin may produce a red-orange discoloration of the urine; this is a harmless side effect that goes away when the drug is discontinued.

Major: Tell your doctor about any side effects that are persistent or particularly bothersome. IT IS ESPECIALLY IMPORTANT TO TELL YOUR DOCTOR about bloody or black, tarry stools; blood in your sputum; fever; heavy bleeding from cuts; internal bleeding (signs of internal bleeding include abdominal pain or swelling and vomiting of blood or material that resembles coffee grounds); loss of hair; mouth sores; nausea; nosebleeds; rash; red urine; severe bruising; severe headache; swelling of joints; unusually heavy menstrual bleeding; or yellowing of the eyes or skin.

Interactions

Warfarin interacts with many other types of drugs:

  • Alcohol, allopurinol, amiodarone, anabolic steroids, antibiotics, chloral hydrate, chloramphenicol, chlorpropamide, cimetidine, clofibrate, danazol, disulfiram, erythromycin, glucagon, isoniazid, ketoconazole, methyldopa, methylphenidate, metronidazole, monoamine oxidase (MAO) inhibitors, nalidixic acid, propoxyphene, quinidine, quinine, salicylates, sulfamethoxazole and trimethoprim combination, sulfinpyrazone, sulfonamides, sulindac, tetracycline, thyroid hormones, and tolbutamide can increase the effects of warfarin, which can be dangerous.

  • Azathioprine, barbiturates, carbamazepine, cholestyramine, colestipol, estrogens, ethchlorvynol, griseofulvin, oral contraceptives (birth control pills), phenytoin, propylthiouracil, rifampin, sucralfate, and vitamin K can decrease the effectiveness of warfarin when taken concurrently.

  • Adrenocorticosteroids (cortisonelike medications), anticancer drugs, aspirin, diflunisal, dipyridamole, fenoprofen, ibuprofen, indomethacin, oxyphenbutazone, phenylbutazone, potassium, quinidine, quinine, and salicylates can increase the bleeding complications of warfarin.

  • Warfarin can increase the side effects of oral antidiabetic agents and phenytoin.

  • Diuretics may either increase the effects or decrease the effectiveness of warfarin. Be sure to ask your doctor about the safety of concurrent use of diuretics and warfarin.

  • While taking warfarin, do not start or stop taking any over-the-counter (nonprescription) medications or supplements, including herbal products such as Saint-John's-wort, ginseng, garlic, or coenzyme Q10, unless recommended by your doctor or pharmacist.

Before starting to take warfarin, BE SURE TO TELL YOUR DOCTOR about any medications (both prescription and nonprescription) you are currently taking, especially any of those listed above.

Warnings

  • Tell your doctor about unusual or allergic reactions you have had to any medications, especially to warfarin.

  • Before starting treatment with this medication, BE SURE TO TELL YOUR DOCTOR if you now have or ever had any condition for which bleeding is an added risk, such as an aneurysm, blood disorders, cancer, diabetes mellitus, congestive heart failure, edema, endocarditis, high blood pressure, indwelling catheters, intestinal infections, kidney or liver disease, malnutrition, menstrual difficulties, pericarditis, surgery, thyroid disease, tuberculosis, ulcers, vasculitis, or wounds and injuries.

  • Before having surgery or any other medical or dental treatment, BE SURE TO TELL YOUR DOCTOR OR DENTIST that you are taking warfarin.

  • Do not take any aspirin-containing products or any over-the-counter products while you are on warfarin, unless you first check with your doctor or pharmacist. Aspirin can increase the risk of bleeding complications from warfarin.

  • Avoid any activity, such as a contact sport, that might lead to physical injury. Tell your doctor about any fall or blow that occurs. Warfarin can cause heavy bleeding from cuts.

  • Use an electric razor while shaving to reduce the risk of cutting yourself, and be especially gentle and careful while brushing your teeth.

  • Since factors as diverse as travel, diet, the environment, and your general health can affect your body's response to warfarin, your dosage level should be carefully monitored by your doctor.

  • Do not stop taking warfarin unless you first consult your doctor. If you stop taking this drug abruptly, you may experience unwanted blood clotting. Your doctor may, therefore, want to reduce your dosage gradually.

  • Do not change brands of warfarin without consulting your doctor.

  • Avoid changes in your diet, as this can affect how warfarin works. It is particularly important not to eat more or less foods with a high content of vitamin A (such as green, leafy vegetables). Discuss this with your doctor or pharmacist.

  • Some of these products contain the color additive FD&C Yellow No. 5 (tartrazine), which can cause allergic-type reactions in certain susceptible individuals.

  • Be sure to tell your doctor if you are pregnant. Warfarin has been associated with birth defects and bleeding complications in fetuses. Also tell your doctor if you are breast-feeding an infant.