Warfarin (Injection)


Warfarin (WAR-far-in)
Helps to prevent new blood clots from forming, and helps to keep existing blood clots from getting worse. This medicine is a blood thinner (anticoagulant).

Brand Name(s)

There may be other brand names for this medicine.


When This Medicine Should Not Be Used

You should not receive this medicine if you have had an allergic reaction to warfarin, or if you are pregnant or planning to become pregnant. Ask your doctor about using this medicine if you are having or have recently had surgery. Usually, you should not use this medicine if you are having surgery on your eyes, brain, or spine, or major surgery that will leave you with large, open wounds. This medicine should not be used if you have certain heart problems, severe or uncontrolled high blood pressure, or any condition that may cause uncontrolled bleeding (such as a stomach ulcer or hemophilia).

How to Use This Medicine

  • A nurse or other trained health professional will give you this medicine.
  • Your doctor will prescribe your exact dose and tell you how often it should be given. This medicine is given through a needle placed in one of your veins.
  • Your doctor will only give you a few doses of this medicine, and then you may be switched to an oral medicine that works the same way. If you have any concerns about this, talk to your doctor.

Drugs and Foods to Avoid

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.
  • Do not use other medicines that also contain warfarin. Using too much warfarin may cause serious bleeding problems.
  • There are many other medicines that you should not use while you are using warfarin. These include many herbs, supplements, and over-the-counter (nonprescription) medicines. Ask your doctor before you use any other medicine, especially products that contain nonsteroidal antiinflammatory drugs (NSAIDs) such as aspirin, ibuprofen, naproxen, Advil®, Aleve®, or Motrin®. Carefully check the labels of all other medicines you are using to be sure they do not contain NSAIDs.
  • Carefully follow your doctor's instructions about any special diet. This medicine works best when you eat about the same amount of vitamin K in your food every day. Avoid big changes in how much vitamin K you eat. Some foods that have a high amount of vitamin K are asparagus, broccoli, brussels sprouts, cabbage, green leafy vegetables (such as collards, turnip greens, mustard greens, spinach, and salad greens), plums, rhubarb, and certain vegetable oils (such as soybean oil and canola oil).
  • Avoid taking a large quantity of cranberry juice or other cranberry products.
  • Do not drink alcohol while you are using this medicine.

Warnings While Using This Medicine

  • Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using the medicine, tell your doctor right away.
  • Make sure your doctor knows if you are breastfeeding, or if you have kidney disease, liver disease, congestive heart failure, or high blood pressure. Tell your doctor if you have had any recent illnesses or infections, or a fall or other injuries. Make sure your doctor knows if you have bleeding problems, diabetes, or any other medical problems. Tell your doctor if you have a rare hereditary condition called protein C deficiency.
  • You may bleed and bruise more easily while you are using this medicine. Stay away from rough sports or other situations where you could be bruised, cut, or injured. Brush and floss your teeth gently. Be careful when using sharp objects, including razors and fingernail clippers. Avoid picking your nose. If you need to blow your nose, blow it gently.
  • Tell your doctor right away if you start to have diarrhea, fever, or any signs of infection.
  • Carry an ID card or wear a medical alert bracelet so that during an emergency, health caregivers will know that you are using warfarin.
  • This medicine may cause skin necrosis or gangrene. Call your doctor right away if you have a pain, color change, or temperature change to any area of your body. Also, call your doctor right away if you have a pain in your toes and they look purple or dark in color. These could be signs of a serious medical problem.
  • Do not stop taking any of your medicines or start any new medicines unless they have been discussed with your doctor. Always keep a list of your medicines with you at all times.
  • Make sure any doctor or dentist who treats you knows that you are using this medicine. You may need to stop using this medicine several days before having surgery or medical tests.
  • It is very important that your doctor checks your progress at regular visits to see if the medicine is working properly. Blood tests, such as INR, are needed to check for proper dosage and unwanted side effects. Be sure to keep all appointments.

Possible Side Effects While Using This Medicine

Call your doctor right away if you notice any of these side effects:
  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing.
  • Bleeding from your gums or nose, bruising easily, or coughing up blood.
  • Blistering, soreness, or redness of the skin.
  • Chest pain, shortness of breath, or trouble with breathing or swallowing.
  • Cold clammy skin, confusion, fast, weak pulse, or sweating.
  • Decrease in how much or how often you urinate, or trouble urinating.
  • Dizziness, fainting, lightheadedness, or trouble thinking clearly.
  • Fever, chills, sore throat, or cough.
  • Heavy menstrual bleeding, or bleeding from cuts or wounds that does not stop.
  • Numbness, tingling, or weakness anywhere in your body, or problems with movement, swallowing, or speech.
  • Pain, color change, or temperature change to any area of your body.
  • Pain, itching, burning, swelling, or a lump under your skin where the needle is placed.
  • Painful, prolonged erection of your penis.
  • Purple discoloration of your toes or feet, or new pain in a leg, foot, or your toes.
  • Red or dark brown urine, or red or black stools.
  • Sudden or severe headache, or new pain in your abdomen (belly), flank (sides), or back.
  • Swelling in your hands, ankles, or feet.
  • Unusual bleeding, bruising, or weakness.
  • Unusual drowsiness, tiredness, or loss of consciousness.
  • Vomiting of blood or material that looks like coffee grounds.
  • Yellowing of your skin or the whites of your eyes.
If you notice these less serious side effects, talk with your doctor:
  • Hair loss.
  • Headache, muscle or joint pains.
  • Nausea, vomiting, diarrhea, or upset stomach.
  • Pale skin or rash.
  • Unusual or unpleasant taste.

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088
Review Date: 2011-02-04 Reviewed By: Keywords: ,
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