Prescription vs.OTC: Prescription by Doctor required
Last Updated: September 16, 2021

Warfarin is primarily used as prophylaxis and treatment of venous thrombosis, pulmonary embolism and thromboembolic disorders; atrial fibrillation with risk of embolism and as an adjunct in the prophylaxis of systemic embolism after myocardial infarction.

Warfarin is an anticoagulant and is used to help reduce the formation of blood clots. As it is a blood thinner, it works by preventing the formation of blood clots in arteries or veins, thus reducing the risk of heart attack, stroke, or other serious conditions.

Do not take Warfarin if you have a blood cell disorder, if you have a bleeding disorder, if you have high blood pressure, if you have a history of stomach bleeding, bleeding in your brain or an upcoming surgery. Before using Warfarin tell your doctor if you are using any prescription drugs, non-prescription drugs, or other herbal and dietary pills and supplements, if you are allergic to certain food items or substances, if you are pregnant and/or breastfeeding, if you have a blood cell disorder, of if you have a history of kidney diseases.

Warfarin is administered either orally or intravenously, depending on the patient and the specific condition he is being treated for. Common side effects of Warfarin include nausea, stomach pain, vomiting, gas, bloating or an altered sense of taste.

Symptoms of overdose include internal or external hemorrhage and hematuria. Avoid emesis and lavage to avoid possible trauma and incidental bleeding. When an overdose occurs, the drug should be immediately discontinued and vitamin K1 (phytonadione) may be administered, up to 25 mg I.V. for adults.

When hemorrhage occurs, fresh frozen plasma transfusions can help control bleeding by replacing clotting factors. In urgent bleeding, prothrombin complex concentrates may be needed.

Take exactly as directed; if dose is missed, take as soon as possible. Do not double doses. Do not take any medication your prescriber is not aware of and follow diet and activity as recommended by prescriber.

You may have a tendency to bleed easily while taking this drug; brush teeth with soft brush, floss with waxed floss, use electric razor, and avoid scissors or sharp knives and potentially harmful activities. You may experience nausea or vomiting (small frequent meals, frequent mouth care, sucking lozenges, or chewing gum may help).

May discolor urine or stool. Report skin rash or irritation, unusual fever, persistent nausea or GI upset, unusual bleeding or bruising (bleeding gums, nosebleed, blood in urine, dark stool, bloody emesis), pain in joints or back, swelling or pain at injection site.

Information given here is based on the salt content of the medicine. Uses and effects of the medicine may vary from person to person. It is advisable to consult a Hematologist before using this medicine.

The medication is primarily used for the following conditions:

Below are some of the common side effects of this medicine:

  • Are there any pregnancy warnings?

    Warfarin is highly unsafe to use during pregnancy.
    Human and animal studies have shown significant adverse effects on the foetus. Please consult your doctor.
  • Are there any breast-feeding warnings?

    This medicine does not pass into breast milk and can be given to nursing mothers. Warfarin is probably safe to use during breastfeeding. Please consult your doctor.
  • Is it safe to drive while on this medicine?

    There is no data available. Please consult doctor before consuming the drug.
  • Does this affect kidney function?

    There is no interaction between renal impairment and consuming this drug. So dose alteration is not needed.
  • Does this affect liver function?

    Monitor effect at usual doses; the response to oral anticoagulants may be markedly enhanced in obstructive jaundice (due to reduced vitamin K absorption) and also in hepatitis and cirrhosis (due to decreased production of vitamin K-dependent clotting factors); prothrombin index should be closely monitored. Please consult doctor before consuming the drug.
  • What is the onset of action?

    The effect of this medicine is initiated within 36-72 hours after its oral administration.
  • How long is the duration of effect?

    The effect of this medicine will remain for about 42 hours.
  • Are there any missed dose instructions?

    If you miss a dose of Warfarin, skip it and continue with your normal schedule. Do not double the dose.

Below is the list of medicines, which contains Warfarin as ingredient

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This medication acts as an anticoagulant which prevents the regeneration of vitamin K1 epoxide which in turn inhibits the formation of Vitamin K dependent coagulation factors like Factor II, VII, X and IX as well as the anticoagulant proteins S and C.

Whenever you take more than one medicine, or mix it with certain foods or beverages, you"re at risk of a drug interaction.

  • Interaction with Alcohol

    Chronic use of alcohol inhibits warfarin metabolism; avoid or limit use.
  • Interaction with Medicine

    • Induction of enzymes: Barbiturates, carbamazepine, glutethimide, griseofulvin, nafcillin, phenytoin, rifampin.
    • Increased procoagulant factors: Estrogens, oral contraceptives, vitamin K (including nutritional supplements).
    • Decreased drug absorption: Aluminum hydroxide, cholestyramine*, colestipol*.
    • Other: Ethchlorvynol, griseofulvin, spironolactone**, sucralfate.
    • *Cholestyramine and colestipol may increase the anticoagulant effect by binding vitamin K in the gut; yet, the decreased drug absorption appears to be of more concern. **Diuretic-induced hemoconcentration with subsequent concentration of clotting factors has been reported to decrease the effects of oral anticoagulants.
    • Increased bleeding tendency: (Use of these agents with oral anticoagulants may increase the chances of hemorrhage.)
    • Inhibit platelet aggregation: Cephalosporins, dipyridamole, indomethacin, oxyphenbutazone, penicillin (parenteral), phenylbutazone, salicylates, sulfinpyrazone.
    • Inhibit procoagulant factors: Antimetabolites, quinidine, quinine, salicylates.
    • Ulcerogenic drugs: Adrenal corticosteroids, indomethacin, oxyphenbutazone, phenylbutazone, potassium products, salicylates.
    • Enhanced anticoagulant effects:
      • Decrease Vitamin K: Oral antibiotics can increase or decrease INR. Check INR 3 days after patient begins antibiotics to see the INR value and adjust the warfarin dose accordingly.
      • Displace anticoagulant: Chloral hydrate, clofibrate, diazoxide, ethacrynic acid, miconazole, nalidixic acid, phenylbutazone, salicylates, sulfonamides, sulfonylureas, triclofos.
      • Inhibit Metabolism: Alcohol (acute ingestion)*, Allopurinol, amiodarone, chloramphenicol, chlorpropamide, cimetidine, co-trimoxazole, disulfiram, metronidazole, phenylbutazone, phenytoin, propoxyphene, sulfinpyrazone, sulfonamides, tolbutamide.
      • Other: Acetaminophen, anabolic steroids, clofibrate, danazol, erythromycin, gemfibrozil, glucagon, influenza vaccine, ketoconazole, propranolol, ranitidine, sulindac, thyroid drugs, capecitabine, celecoxib, rofecoxib.
      *The hypoprothrombinemic effect of oral anticoagulants has been reported to be both increased and decreased during chronic and excessive alcohol ingestion. Data are insufficient to predict the direction of this interaction in alcoholic patients.
  • Interaction with Food

    • Vitamin K: Foods high in vitamin K (eg, beef liver, pork liver, green tea and leafy green vegetables) inhibit anticoagulant effect. Do not change dietary habits once stabilized on warfarin therapy; a balanced diet with a consistent intake of vitamin K is essential; avoid large amounts of alfalfa, asparagus, broccoli, Brussels sprouts, cabbage, cauliflower, green teas, kale, lettuce, spinach, turnip greens, watercress. It is recommended that the diet contain a CONSISTENT vitamin K content of 70-140 mcg/day. Check with physician before changing diet.
    • Vitamin E: May increase warfarin effect; do not change dietary habits or vitamin supplements once stabilized on warfarin therapy.
  • Interaction with Disease

    • Cautious use in severe renal disease, although has been used. Hemorrhage is the most serious risk. Have patient report any signs or symptoms of bleeding or any falls or accidents immediately.
    • Patient must also report any new or discontinued medications, herbal or alternative products used, significant changes in smoking or eating habits.
    • Necrosis or gangrene of the skin and other tissues can rarely occur due to early hypercoagulability.
    • "Purple toes syndrome," due to cholesterol microembolization, may rarely occur (often after several weeks of therapy).
    • Women may be at risk of developing ovarian hemorrhage at the time of ovulation.
    • Use with caution in traumas, infection (antibiotics and fever may alter affects), renal insufficiency, prolonged dietary insufficiencies (vitamin K deficiency), moderate-severe hypertension, polycythemia vera, vasculitis, open wound, active TB, history of PUD, anaphylactic disorders, indwelling catheters, severe diabetes, and menstruating and postpartum women.
    • Use with caution in protein C deficiency.
    • The elderly may be more sensitive.
    • Use care in selection of patients appropriate for this treatment.
    • Ensure patient cooperation especially from the alcoholic, illicit drug user, demented, or psychotic patient.

Ques: What is Warfarin used for?

Ans: Warfarin is used to help reduce the formation of blood clots.

Ques: What is the onset of action of Warfarin?

Ans: Warfarin takes approximately 36 to 48 hours to show its effect.

Ques: How long does the effect of Warfarin last?

Ans: The effect of Warfarin lasts between 2 to 5 days.

Ques: Where is Warfarin approved?

Ans: Warfarin is approved in India, Micronesia, Japan, and the USA.

Ques: Should Warfarin be taken with a meal or without a meal?

Ans: Warfarin can be taken either way as its effectiveness does not depend on a meal.

Ques: What are the dietary restrictions while taking Warfarin?

Ans: There are no specific dietary restrictions while taking Warfarin unless the doctor instructs otherwise.

Ques: Is it safe to stop taking Warfarin suddenly?

Ans: It is advised to not stop taking Warfarin suddenly as doing so may induce severe side-effects.
Disclaimer: The information produced here is best of our knowledge and experience and we have tried our best to make it as accurate and up-to-date as possible, but we would like to request that it should not be treated as a substitute for professional advice, diagnosis or treatment.

Lybrate is a medium to provide our audience with the common information on medicines and does not guarantee its accuracy or exhaustiveness. Even if there is no mention of a warning for any drug or combination, it never means that we are claiming that the drug or combination is safe for consumption without any proper consultation with an expert.

Lybrate does not take responsibility for any aspect of medicines or treatments. If you have any doubts about your medication, we strongly recommend you to see a doctor immediately.

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Written By
PhD (Pharmacology) Pursuing, M.Pharma (Pharmacology), B.Pharma - Certificate in Nutrition and Child Care
Reviewed By
MBBS, Master in Healthcare Administration, Diploma in Occupational Health
General Physician
Table of Content
About Warfarin
What are the uses of Warfarin
What are the contraindications of Warfarin ?
What are the side effects of Warfarin ?
Key highlights of Warfarin
What are the dosage instructions?
Medicines containing Warfarin
How does this medication work?
What are the interactions of Warfarin ?
FAQs about Warfarin