Warfarin and Superwarfarin Toxicity Clinical Presentation

Updated: Sep 12, 2023
  • Author: Kent R Olson, MD, FACEP; Chief Editor: David Vearrier, MD, MPH  more...
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Bleeding is the only expected significant clinical manifestation. Internal bleeding may present as any of a vast array of symptoms or be occult. Other possible signs and symptoms include [14] :

  • Skin necrosis
  • Vasculitis
  • Calciphylaxis
  • Diarrhea
  • Renal acidosis

Obtain an accurate history of the amount of warfarin or superwarfarin ingested, when it was ingested, and over what period it was ingested. Additionally, inquire about the circumstances of the ingestion to determine the patient's disposition. If the ingestion was suicidal or surreptitious in nature, the history may be difficult to obtain or the patient or caregiver may give misleading information.

An accurate medication list is important because many drugs increase or decrease the metabolism of warfarin (see Overview/Etiology).

The toxic dose of warfarin is highly variable. Generally, a single ingestion of warfarin (10-20 mg) does not cause serious intoxication. In contrast, long-term or repeated ingestion of even small amounts of warfarin (2-5 mg/day) eventually can lead to significant anticoagulation, especially in the presence of interacting drugs. Patients with hepatic dysfunction, malnutrition, or a bleeding diathesis are at the greatest risk of toxicity from warfarin use.

Superwarfarins are extremely potent and can produce prolonged effects even after a small ingestion; as little as 1 mg in an adult can cause coagulopathy.


Physical Examination

Do not expect to see physical evidence of bleeding after an acute ingestion for at least 24 hours. Life-threatening complications include massive gastrointestinal bleeding and intracranial hemorrhage. More common findings of excessive anticoagulation are ecchymoses, subconjunctival hemorrhage, epistaxis, vaginal bleeding, bleeding gums, or hematuria.

In all patients, if prolongation of the prothrombin time (PT) is observed after an acute ingestion, it may appear in as early as 8-12 hours; however, peak effects commonly are delayed until at least 1-2 days postingestion.

Skin necrosis is a rare but serious manifestation of toxicity and usually occurs within a few days of starting therapy but has been reported up to three years later.  Due to the increased subcutaneous fat, the most common sites of necrosis are breasts, abdomen, buttocks, calves and thighs. [15]