Who Should Not Take Warfarin?
Warfarin is contraindicated in patients with active bleeding or conditions with high bleeding risk, such as recent hemorrhagic stroke, active peptic ulcer, or intracranial hemorrhage. It is also avoided in those with hypersensitivity to warfarin or its components.[1]
Why Is It Unsafe in Pregnancy?
Warfarin causes fetal harm, including embryopathy (nasal hypoplasia, stippled epiphyses) in the first trimester and hemorrhage or CNS abnormalities later in pregnancy. It is contraindicated in women who are pregnant or may become pregnant, except in specific life-threatening situations under specialist oversight.[1][2]
What About Bleeding Disorders?
Patients with hemophilia, thrombocytopenia, or other coagulopathies cannot use warfarin, as it worsens clotting defects and increases hemorrhage risk.[1]
Mechanical Heart Valves and Recent Surgery
Avoid warfarin within 24-48 hours post-major surgery or in early postoperative periods with high bleeding potential. It is also contraindicated short-term after prosthetic heart valve placement until endothelialization occurs.[1]
Why Avoid with Certain Health Conditions?
- Uncontrolled hypertension (systolic >170 mmHg or diastolic >100 mmHg), due to stroke risk.
- Severe liver disease or failure, which impairs clotting factor synthesis.
- Infectious diseases like bacterial endocarditis, which heighten embolic or hemorrhagic risks.
- Recent or planned invasive procedures with bleeding concerns.[1][2]
Drug Interactions Leading to Contraindication
Warfarin interacts dangerously with drugs that amplify anticoagulation, such as certain cephalosporins, moxalactam, or high-dose salicylates (>2g/day). It is contraindicated if these cannot be discontinued or monitored closely.[1]
How Do Alcohol and Diet Play a Role?
Excessive alcohol intake contraindicates warfarin due to liver toxicity and variable metabolism. Rapid changes in vitamin K intake (e.g., from diet or supplements) can destabilize INR, making it unsafe without strict control.[2]
[1]: FDA Label for Coumadin (warfarin)
[2]: UpToDate: Warfarin and other vitamin K antagonists