Anticoagulant (Warfarin and Rodenticide Superwarfarin) Poisoning

Description

General measures

Medicine treatment

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T45.5 + (X44.99/X64.99/Y14.99)
* Notifiable condition – rodenticide superwarfarin poisoning

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Poisoning from all pesticides (i.e. agricultural stock remedies) is a notifiable medical condition. Please visit https://nicd.ac.za/nmc-overview/notification-process for further information.

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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.

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

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GENERAL MEASURES

• Resuscitation.
• Stop warfarin in patients on therapy.
• Measure INR at baseline and 48 hours post ingestion, as the anticoagulant effect may be delayed by 1–2 days.

MEDICINE TREATMENT

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Do NOT give vitamin K₁ prophylactically. It is only indicated when there is active bleeding or a specifically raised INR (INR > 4).

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Active bleeding:
R58 + (T45.5 + X44.99/X64.99/Y14.99)

• Lyophilised plasma, IV, 15 mL/kg.

OR

• Fresh Frozen Plasma, IV, 15 mL/kg.

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AND

• Vitamin K₁, IV, 10 mg
  • Administer as a slow IV injection.
  • Do not dilute or mix with other injectables.

For patients on long term vitamin K antagonist anticoagulants, e.g. warfarin:

• Temporarily discontinue anticoagulant therapy.
• Decrease Vitamin K dose by half, i.e. Vitamin K1, IV, 5 mg. Administer as a slow IV injection.

LoE:IV

No bleeding but INR is raised (INR > 4):

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Note:
If Vitamin K₁ is only available as a parenteral preparation, administer the same preparation orally as this is safest in anticoagulant poisoning.

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Patients NOT on long-term therapeutic anticoagulants and INR > 4.0:

• Vitamin K₁, oral, 10-20 mg.
  • Check INR at least 12 hours after vitamin K₁ has been administered. Repeated doses should be guided by further INR (or PT) measurements every 4-6 hours until the patient is stable, and thereafter, every 24 hours. INR (or PT) levels may take 3-4 days to normalise.

Patients on long-term vitamin K antagonist anticoagulant drugs (e.g. warfarin therapy):

If INR 5-8:

• Temporarily discontinue any anticoagulant treatment.

If INR > 8:

• Vitamin K1, oral, 0.5 – 1.0 mg (one tenth of the normal dose).
  • A repeat dose may be given 12-24 hrs later if the INR remains ≥ 8.

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Note:
- These patients are complex and require management in consultation with a haematologist.
- Patients with prosthetic heart valves receiving high-dose vitamin K have a higher risk for increased resistance to warfarin and development of thromboembolism. Treat as above but monitor INR frequently to prevent overcorrection. Treat in consultation with a specialist.
- For patients on other anticoagulant therapies, additional antagonists may be required.
- In all patients on therapeutic warfarin, a major overdose or bleeding episode should prompt careful review of the need for anticoagulation.
- Warfarin should be re-started once the INR is in the therapeutic range if it is still indicated.
- In patients with superwarfarin toxicity, treatment with vitamin K1 may need to be prolonged for several months as superwarfarins are very long acting. Discuss with the Poisons Information Centre or haematologist for advice on dosing and duration of treatment.

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Click here to access the pdf.

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Standard Treatment Guidelines and Essential Medicines List for South Africa, Adult Hospital Level, 2020-2024_Version 2.0_27 March 2025

Chapter 19 Poisoning_19.19 Anticoagulant (Warfarin and Rodenticide Superwarfarin) Poisoning