Antidote and clotting factor replacement

The antidote, phytomenadione (vitamin K₁), is the only vitamin K analogue effective for treatment of superwarfarin poisoning; do not use menadione (vitamin K₃) or any other vitamin K analogue. Much larger doses of phytomenadione (vitamin K₁) are required and for a more protracted period than for warfarin poisoning. Do not give phytomenadione (vitamin K₁) before anticoagulation is apparent on INR measurement because it delays the onset of anticoagulation.

The aim of phytomenadione (vitamin K₁) therapy is to maintain an INR less than 2. Treatment may be required for many weeks or months because elimination of superwarfarins is slow. It may be difficult to determine the appropriate initial dose of phytomenadione (vitamin K₁); it is safest to start with a relatively large dose and titrate to maintain an INR less than 2. Consult a clinical toxicologist for advice, particularly for dosing in children.

Phytomenadione (vitamin K1) initially can be given orally or intravenously. It has low oral bioavailability (50%),and is less effective if the patient has received gastrointestinal decontamination with activated charcoal. Oral therapy is recommended for patients who are not bleeding, can tolerate oral therapy and have not received activated charcoal.

For adults with an INR more than 2 due to superwarfarin ingestion, if oral phytomenadione (vitamin K) therapy is appropriate, use:

For adults with an INR more than 2 due to superwarfarin ingestion, if intravenous phytomenadione (vitamin K) therapy is appropriate, use:

For patients with an INR more than 10, use the upper end of the dose range.

Monitor the INR daily until it has stabilised below 2. If treatment was initially given intravenously, switch to oral dosing. Check the INR remains below 2 for at least 2 days before discharge. Discharge patients with follow up and monitor the INR weekly to ensure adherence. Continue phytomenadione (vitamin K₁) for at least 1 month. Phytomenadione (vitamin K₁) can be weaned if the INR remains normal—seek advice from a clinical toxicologist about the duration of therapy and weaning therapy.

If the patient is actively bleeding, to replace clotting factors, add: