Anticoagulant (warfarin and rodenticide superwarfarin) poisoning

T45.5 + (X44.99/X64.99/Y14.99)

* Notifiable condition – rodenticide superwarfarin poisoning

DESCRIPTION

Poisoning due to ingestion of warfarin and superwarfarins, e.g. rat poison and other vermin poisons.

Warfarin toxicity can occur with either acute overdose or unintentionally, during therapeutic use, whereby drug interactions increase warfarin bioavailability (e.g. concomitant enzyme inhibitor), or concomitant anticoagulant drugs are administered (e.g. NSAIDS).

Bleeding is the main clinical presentation e.g. gastrointestinal or intracranial bleeding; however bleeding may be occult.

Superwarfarins are more potent than warfarin and may have a long duration of effect; small doses of concentrated formulations may cause significant anticoagulation.

Measure INR at baseline and 48 hours post ingestion, as the anticoagulant effect may be delayed by 1–2 days.

Where the history is of an unspecified rat poison or pesticide ingestion, consider other active ingredients such as amitraz and organophosphates.

GENERAL MEASURES

Resuscitation.
Stop warfarin in patients on therapy.

MEDICINE TREATMENT

For patients on warfarin therapy

INR 5 to 9 without bleeding:

  • Stop warfarin
  • Evaluate bleeding risk
    • High risk patients: (history of bleeding, stroke, renal insufficiency, anaemia, hypertension).
      • Vitamin K1 oral, 1–2.5 mg, for 1–2 days and monitor INR.
    • Low risk patients: Monitor INR.

INR > 9 without bleeding:

  • Stop warfarin.
    • Vitamin K1 oral, 2.5–5 mg, for 1–2 days and monitor INR (response usually in 24 to 48 hrs).
  • Resume warfarin therapy, at a lower dose.

Vitamin K1 is available as a parenteral preparation only, but is safest given orally in anticoagulant poisoning.

LoEI [65]

Elevated INR with significant bleeding: R58 + (T45.5/X44.99/X64.99/Y14.99)

  • Stop warfarin.
  • Lyophilised plasma, IV, 15 mL/kg.

LoEIII [66]

OR

  • FFP 15 mL/kg.

LoEII [67]

Followed by:

  • Vitamin K1, IV,10 mg diluted in 100 mL sodium chloride 0.9% over 20 minutes and monitor for prophylaxis.

LoEIII [68]

Note:

  • In patients with prosthetic heart valves, high dose vitamin K is associated with increased resistance to warfarin and increased risk of thromboembolism. Treat as above, but monitor INR frequently to prevent overcorrection in consultation with a specialist.
  • In all patients on therapeutic warfarin, a major overdose or bleeding episode should prompt careful review of the need for anticoagulation
  • If warfarin is indicated it should be re-instituted, once the INR is in the therapeutic range.

Rodenticide ingestion - Superwarfarins

Do not given prophylactic vitamin K.

LoEIII [69]

INR >4 or the patient is actively bleeding:

  • Vitamin K1 oral, 10–25 mg, daily may be required.

Vitamin K1 is available as a parenteral preparation only, but is safest given orally in anticoagulant poisoning.

Treatment with vitamin K1 may need to be prolonged for several months as superwarfarins are very long acting.