Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants (‘blood thinners’). It works by decreasing the clotting ability of the blood.
Side Effects Of Warfarin
Warfarin may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
If you experience any of the following symptoms or those listed in the IMPORTANT WARNING section, call your doctor immediately:
- difficulty breathing or swallowing
- swelling of the face, throat, tongue, lips, or eyes
- chest pain or pressure
- swelling of the hands, feet, ankles, or lower legs
- extreme tiredness
- lack of energy
- loss of appetite
- pain in the upper right part of the stomach
- yellowing of the skin or eyes
- flu-like symptoms
- You should know that warfarin may cause necrosis or gangrene (death of skin or other body tissues). Call your doctor immediately if you notice a purplish or darkened color to your skin, skin changes, ulcers, or an unusual problem in any area of your skin or body, or if you have severe pain that occurs suddenly, or color or temperature change in any area of your body. Call your doctor immediately if your toes become painful or become purple or dark in color. You may need medical care right away to prevent amputation (removal) of your affected body part.
Warfarin may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.
Warnings & Precautions
Before taking warfarin:
- tell your doctor and pharmacist if you are allergic to warfarin, any other medications, or any of the ingredients in warfarin tablets. Ask your pharmacist or check the Medication Guide for a list of the ingredients.
- do not take two or more medications that contain warfarin at the same time. Be sure to check with your doctor or pharmacist if you are uncertain if a medication contains warfarin or warfarin sodium.
- tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, and nutritional supplements you are taking or plan to take, especially acyclovir (Zovirax); allopurinol (Zyloprim); alprazolam (Xanax); antibiotics such as ciprofloxacin (Cipro), clarithromycin (Biaxin, in Prevpac), erythromycin (E.E.S., Eryc, Ery-Tab), nafcillin, norfloxacin (Noroxin), sulfinpyrazone, telithromycin (Ketek), and tigecycline (Tygacil); anticoagulants such as argatroban (Acova), dabigatran (Pradaxa), bivalirudin (Angiomax), desirudin (Iprivask), heparin, and lepirudin (Refludan); antifungals such as fluconazole (Diflucan), itraconazole (Onmel, Sporanox), ketoconazole (Nizoral), miconazole (Monistat), posaconazole (Noxafil), terbinafine (Lamisil), voriconazole (Vfend); antiplatelet medications such as cilostazol (Pletal), clopidogrel (Plavix), dipyridamole (Persantine, in Aggrenox), prasugrel (Effient), and ticlopidine (Ticlid); aprepitant (Emend); aspirin or aspirin-containing products and other nonsteroidal anti-inflammatory drugs such as celecoxib (Celebrex), diclofenac (Flector, Voltaren, in Arthrotec), diflunisal, fenoprofen (Nalfon), ibuprofen (Advil, Motrin), indomethacin (Indocin), ketoprofen, ketorolac, mefenamic acid (Ponstel), naproxen (Aleve, Naprosyn), oxaprozin (Daypro), piroxicam (Feldene), and sulindac (Clinoril); bicalutamide; bosentan; certain antiarrhythmic medications such as amiodarone (Cordarone, Nexterone, Pacerone), mexiletine, and propafenone (Rythmol); certain calcium channel blocking medications such as amlodipine (Norvasc, in Azor, Caduet, Exforge, Lotrel, Twynsta), diltiazem (Cardizem, Cartia XT, Dilacor XR, Tiazac) and verapamil (Calan, Isoptin, Verelan, in Tarka); certain medications for asthma such as montelukast (Singulair), zafirlukast (Accolate), and zileuton (Zyflo); certain medications used to treat cancer such as capecitabine (Xeloda), imatinib (Gleevec), and nilotinib (Tasigna); certain medications for cholesterol such as atorvastatin (Lipitor, in Caduet) and fluvastatin (Lescol); certain medications for digestive disorders such as cimetidine (Tagamet), famotidine (Pepcid), and ranitidine (Zantac); certain medications for human immunodeficiency virus (HIV) infection such as amprenavir, atazanavir (Reyataz), efavirenz (Sustiva), etravirine (Intelence), fosamprenavir (Lexiva), indinavir (Crixivan), lopinavir/ritonavir, nelfinavir (Viracept), ritonavir (Norvir), saquinavir (Invirase), and tipranavir (Aptivus); certain medications for narcolepsy such as armodafinil (Nuvigil) and modafinil (Provigil); certain medications for seizures such as carbamazepine (Carbatrol, Equetro, Tegretol), phenobarbital, phenytoin (Dilantin, Phenytek), and rufinamide (Banzel); certain medications to treat tuberculosis such as isoniazid (in Rifamate, Rifater) and rifampin (Rifadin, in Rifamate, Rifater); certain selective serotonin reuptake inhibitors (SSRIs) or selective serotonin and norepinephrine reuptake inhibitors (SNRIs) such as citalopram (Celexa), desvenlafaxine (Pristiq), duloxetine (Cymbalta), escitalopram (Lexapro), fluoxetine (Prozac, Sarafem, in Symbyax), fluvoxamine (Luvox), milnacipran (Savella), paroxetine (Paxil, Pexeva), sertraline (Zoloft), venlafaxine (Effexor) corticosteroids such as prednisone; cyclosporine (Neoral, Sandimmune); disulfiram (Antabuse); methoxsalen (Oxsoralen, Uvadex); metronidazole (Flagyl); nefazodone (Serzone), oral contraceptives (birth control pills); oxandrolone (Oxandrin); pioglitazone (Actos, in Actoplus Met, Duetact, Oseni); propranolol (Inderal) or vilazodone (Viibryd). Many other medications may also interact with warfarin, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list. Do not take any new medications or stop taking any medication without talking to your doctor.
- tell your doctor and pharmacist what herbal or botanical products you are taking, especially coenzyme Q10 (Ubidecarenone), Echinacea, garlic, Ginkgo biloba, ginseng, goldenseal, and St. John’s wort. There are many other herbal or botanical products that might affect your body’s response to warfarin. Do not start or stop taking any herbal products without talking to your doctor.
- tell your doctor if you have or have ever had diabetes. Also tell your doctor if you have an infection, a gastrointestinal illness such as diarrhea, or sprue (an allergic reaction to the protein found in grains that causes diarrhea), or an indwelling catheter (a flexible plastic tube that is placed into the bladder to allow the urine to drain out).
- Tell your doctor if you are pregnant, think you might be pregnant, or plan to become pregnant while taking warfarin. Pregnant women should not take warfarin unless they have a mechanical heart valve. Talk to your doctor about the use of effective birth control while taking warfarin. If you become pregnant while taking warfarin, call your doctor immediately. Warfarin may harm the fetus.
- tell your doctor if you are breast-feeding.
- if you are having surgery, including dental surgery, or any type of medical or dental procedure, tell the doctor or dentist that you are taking warfarin. Your doctor may tell you to stop taking warfarin before the surgery or procedure or change your dosage of warfarin before the surgery or procedure. Follow your doctor’s directions carefully and keep all appointments with the laboratory if your doctor orders blood tests to find the best dose of warfarin for you.
- ask your doctor about the safe use of alcoholic beverages while you are taking warfarin.
- tell your doctor if you use tobacco products. Cigarette smoking may decrease the effectiveness of this medication.
Dosage Of Warfarin
Warfarin comes as a tablet to take by mouth. It is usually taken once a day with or without food. Take warfarin at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take warfarin exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor. Call your doctor immediately if you take more than your prescribed dose of warfarin.
Your doctor will probably start you on a low dose of warfarin and gradually increase or decrease your dose based on the results of your blood tests. Make sure you understand any new dosing instructions from your doctor.
Continue to take warfarin even if you feel well. Do not stop taking warfarin without talking to your doctor.
Carry an identification card or wear a bracelet stating that you take warfarin. Ask your pharmacist or doctor how to obtain this card or bracelet. List your name, medical problems, medications and dosages, and doctor’s name and telephone number on the card.
Tell all your healthcare providers that you take warfarin.
Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription of warfarin.
It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.
All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.