Warfarin (By mouth)
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).
There may be other brand names for this medicine.
When This Medicine Should Not Be Used
Do not use this medicine if you have had an allergic reaction to warfarin, or if you are pregnant or planning to become pregnant. Make sure any doctor or dentist who treats you knows that you are using this medicine. Ask your doctor about using this medicine if you have or have recently had surgery, because you might have bleeding problems. 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
- Your doctor will tell you how much of this medicine to use and how often. Your dose may need to be changed several times in order to find out what works best for you. Do not use more medicine or use it more often than your doctor tells you to.
- You may take this medicine with or without food.
- This medicine should come with a Medication Guide. Read and follow these instructions carefully. Ask your doctor or pharmacist if you have any questions. Ask your pharmacist for the Medication Guide if you do not have one.
If a dose is missed:
- If you miss a dose or forget to use your medicine and it is still the same day, take your missed dose as soon as possible.
- Do not take 2 doses in 1 day.
How to Store and Dispose of This Medicine
- Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.
- Ask your pharmacist, doctor, or health caregiver about the best way to dispose of any outdated medicine or medicine no longer needed.
- Keep all medicine away from children and never share your medicine with anyone.
Drugs and Foods to Avoid
Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.
- Diet and other medicines can affect the PT/INR level.
- Always tell your doctor before you start or stop any other medicine, even if you can buy the medicine without a prescription (over-the-counter). This also includes vitamins and herbs such as ginkgo, echinacea, and St John's wort.
- Always tell your doctor before you make big changes to your regular diet. Food and drink changes that can change your PT/INR include cranberry, grapefruit, and anything that has high amounts of vitamin K. Asparagus, broccoli, brussels sprouts, cabbage, green leafy vegetables (such as collards, turnip greens, mustard greens, spinach, and salad greens), plums, rhubarb, and some vegetable oils (such as soybean oil and canola oil) are all high in vitamin K. Warfarin works best if you eat and drink about the same amount of vitamin K every day.
- Do not take other medicines that also contain warfarin. 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 medicines, including NSAIDs (nonsteroidal antiinflammatory drugs) such as aspirin, ibuprofen, naproxen, Advil®, Aleve®, or Motrin®. Check the labels of all medicines to be sure they do not contain NSAIDs.
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, high blood pressure, diabetes, any type of infection, or bleeding problems. Tell your doctor if you have had recent surgery or injury, protein C deficiency, or a history of problems caused by heparin.
- You must have a blood test such as PT/INR to make sure this medicine is working and is not causing problems. Your doctor will tell you how often you need to have the test done. It is very important that your doctor checks your progress at regular visits. Keep all appointments.
- Diet and other medicines can affect the PT/INR level. Do not start or stop other medicine or change your diet without telling your doctor first.
- Tell your doctor right away if you get hurt or start to have diarrhea, fever, or any signs of infection.
- Carry an ID card or wear a medical alert bracelet to let emergency caregivers know that you use warfarin.
- This medicine may cause skin or tissue damage (gangrene). Call your doctor right away if you have pain, color change, or temperature change in any part of your body. Call your doctor right away if you have a pain in your toes and they look purple or dark. This problem must be treated right away to avoid permanent damage.
- Make sure any doctor or dentist who treats you knows that you are using this medicine. Your doctor might tell you to change the dose or stop using this medicine for a short time. Do not change anything unless your doctor tells you to.
- Keep a list of your medicines with you at all times.
- 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.
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, trouble breathing
- Decrease in how much or how often you urinate
- Dizziness, fainting, or lightheadedness
- Heavy menstrual bleeding, or bleeding from cuts or wounds that does not stop
- Numbness, tingling, or weakness anywhere in your body
- Pain, color change, or temperature change in any area of your body
- Painful, prolonged erection of your penis
- Purple discoloration of your toes or the soles of your feet, or new pain in a leg, foot, or your toes
- Red or dark brown urine, or red or black stools
- Swelling in your hands, ankles, or feet
- Unusual bleeding, bruising, or weakness
- Vomiting blood or material that looks like coffee grounds
- Yellow skin or eyes
If you notice these less serious side effects, talk with your doctor:
- Headache, hair loss
- Mild nausea
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
- Last Reviewed on 06/12/2013
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This page was last updated: September 18, 2013