{
  "id": "warfarin",
  "title": "Warfarin",
  "lang": "en",
  "source_lang": "en",
  "summary": "Warfarin is an oral anticoagulant that inhibits vitamin K recycling and is used to prevent and treat harmful blood clots.",
  "category": "health",
  "subcategory": "drugs",
  "type": "concept",
  "aliases": [
    "Warfarin sodium",
    "Coumadin",
    "Jantoven"
  ],
  "generated_at": "2026-10-13",
  "model": "pro/gpt-6.1-sol",
  "url": "https://aiwiki.page/en/warfarin/",
  "translations": {
    "zh-Hans": {
      "url": "https://aiwiki.page/zh/warfarin/",
      "json": "https://aiwiki.page/zh/warfarin.json"
    }
  },
  "sections": [
    {
      "heading": "",
      "text": "Warfarin is an oral anticoagulant used to prevent and treat thromboembolic disorders—conditions in which blood clots obstruct blood vessels or travel to other parts of the circulation. It reduces the production of functional vitamin K-dependent clotting factors. Although commonly called a “blood thinner,” it does not directly dissolve existing clots or reverse tissue damage already caused by interrupted blood flow. Its dose is individualized using blood tests because the response varies substantially between patients. (dailymed.nlm.nih.gov)"
    },
    {
      "heading": "Mechanism of action",
      "text": "Warfarin is a vitamin K antagonist. It inhibits vitamin K epoxide reductase, an enzyme involved in recycling vitamin K into the reduced form required for the activation of several clotting factors. This reduces the biological activity of factors II, VII, IX, and X, as well as the naturally anticoagulant proteins C and S. Its effect therefore involves both procoagulant and anticoagulant components of blood coagulation. (dailymed.nlm.nih.gov)\n\nThe effect develops gradually as previously produced clotting factors disappear from circulation. An anticoagulant response generally begins within 24 hours, but the peak effect may take 72–96 hours. The differing lifetimes of the affected factors also explain why the effect persists after a dose is stopped. (dailymed.nlm.nih.gov)\n\nPharmaceutical warfarin is a mixture of two enantiomers, designated R and S. S-warfarin is more potent and is metabolized principally by CYP2C9. Drugs that inhibit or induce enzymes involved in warfarin metabolism can consequently alter its anticoagulant effect. (dailymed.nlm.nih.gov)"
    },
    {
      "heading": "Clinical uses",
      "text": "Warfarin is used for the prevention and treatment of venous thrombosis, including deep vein thrombosis, and pulmonary embolism. It is also used to prevent thromboembolic complications associated with atrial fibrillation and heart valve replacement. Its purpose in treating an existing clot is principally to prevent further extension and additional embolic complications, rather than to remove the clot directly. (dailymed.nlm.nih.gov)\n\nIts role differs between clinical settings. The 2023 American atrial fibrillation guideline favors direct oral anticoagulants over warfarin for most eligible patients with atrial fibrillation. Important exceptions include mechanical heart valves and moderate or greater mitral stenosis, for which warfarin retains a central role. These distinctions reflect differences in the evidence for efficacy and safety, rather than interchangeability among anticoagulant drugs. (jacc.org)"
    },
    {
      "heading": "Monitoring and variability",
      "text": "Warfarin treatment is monitored using the international normalized ratio (INR), a standardized measure derived from prothrombin time. Higher INR values indicate a more prolonged clotting time. The intended range depends on the condition being treated; an INR of 2–3 is commonly used for atrial fibrillation, whereas requirements for mechanical valves vary by valve characteristics and other risk factors. (jacc.org)\n\nThe proportion of treatment time spent within the intended INR range is an important measure of anticoagulation control. Both inadequate anticoagulation and excessive anticoagulation have clinical consequences: the former leaves greater thromboembolic risk, while the latter increases bleeding risk. Maintaining an INR within the intended range does not eliminate bleeding altogether. (jacc.org)\n\nDietary vitamin K intake, illness, liver function, and interacting medicines can change the response. Some interactions alter warfarin concentrations; others increase bleeding through separate mechanisms. Aspirin, other antiplatelet drugs, and nonsteroidal anti-inflammatory drugs are examples of medicines associated with increased bleeding when combined with warfarin. (dailymed.nlm.nih.gov)"
    },
    {
      "heading": "Adverse effects and contraindications",
      "text": "The principal serious adverse effect is bleeding, which can be major or fatal. Risk is influenced by anticoagulation intensity, age, previous bleeding, concurrent medicines, and conditions such as hypertension, anemia, and renal impairment. Uncommon serious reactions include skin and tissue necrosis and cholesterol microembolization, which can produce “purple toe syndrome.” (dailymed.nlm.nih.gov)\n\nExposure during pregnancy can cause congenital abnormalities, fetal bleeding, pregnancy loss, and fetal death. U.S. prescribing information contraindicates warfarin during pregnancy except in certain patients with mechanical heart valves at high thromboembolic risk. This exception does not imply absence of fetal risk. (dailymed.nlm.nih.gov)\n\nExcessive anticoagulation can be reversed with vitamin K. Urgent reversal may also involve replacement of clotting factors with prothrombin complex concentrate or plasma. The approach depends on the degree of anticoagulation, the presence and severity of bleeding, and the clinical circumstances. (dailymed.nlm.nih.gov)"
    },
    {
      "heading": "History",
      "text": "Warfarin arose from research into hemorrhagic disease in cattle fed spoiled sweet clover. Karl Paul Link and colleagues at the University of Wisconsin investigated the anticoagulant dicoumarol and developed related compounds. The name combines WARF, the Wisconsin Alumni Research Foundation, with part of “coumarin.” Initially developed as a rodenticide, warfarin sodium received approval for human use in the United States in 1954. Its use following President Dwight D. Eisenhower’s heart attack in 1955 contributed to its wider recognition as a medicine. (warf.org)"
    }
  ],
  "links": [
    "enzyme",
    "protein",
    "enantiomer",
    "metabolism",
    "atrial-fibrillation",
    "aspirin",
    "hypertension",
    "anemia",
    "pregnancy",
    "united-states"
  ],
  "sources": [
    {
      "title": "DailyMed - WARFARIN SODIUM- warfarin tablet",
      "url": "https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=558b7a0d-5490-4c1b-802e-3ab3f1efe760"
    },
    {
      "title": "DailyMed - WARFARIN SODIUM tablet",
      "url": "https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=46a207ef-eccd-4f40-a2b1-b782479fb008"
    },
    {
      "title": "WARFARIN SODIUM - warfarin sodium tablet",
      "url": "https://dailymed.nlm.nih.gov/dailymed/getFile.cfm?setid=4445c26e-ec5c-40f4-956b-93c12fc73c1d"
    },
    {
      "title": "2020 ACC/AHA Heart Valve Disease Guideline: Key Perspectives, Part 3",
      "url": "https://www.acc.org/Latest-in-Cardiology/ten-points-to-remember/2020/12/16/22/01/2020-ACC-AHA-VHD-GL-Pt-3-GL-VHD"
    },
    {
      "title": "Of Rats and Men: Warfarin Becomes World Famous by 1955 - WARF",
      "url": "https://www.warf.org/announcement/of-rats-and-men-warfarin-becomes-world-famous-by-1955/"
    }
  ],
  "license": "https://creativecommons.org/licenses/by/4.0/"
}