Overdose : מינון יתר

4.9 Overdose

The benefit of gastric decontamination is uncertain. If the patient presents within 1 hour of ingestion of more than 0.25 mg/kg or more than the patient's therapeutic dose, consider activated charcoal (50 g for adults; 1 g/kg for children)

In cases of life-threatening haemorrhage
Stop warfarin treatment, give prothrombin complex concentrate (factors II, VII, IX, and X) 30– 50 units/kg or (if no concentrate available) fresh frozen plasma 15 mL/kg. Discuss with local haematologist or National Poisons Information Service, or both.

Non-life threatening haemorrhage
Where anticoagulation can be suspended, give slow intravenous injection of phytomenadione (vitamin K1) 10–20 mg for adults (250 micrograms/kg for a child) Where rapid re-anticoagulation is desirable (e.g., valve replacements) give prothrombin complex concentrate (factors II, VII, IX, and X) 30–50 units/kg or (if no concentrate available) fresh frozen plasma 15 mL/kg.
Monitor INR to determine when to restart normal therapy. Monitor INR for at least 48 hours post overdose.

For patients on long-term warfarin therapy without major haemorrhage
• INR >8.0, no bleeding or minor bleeding—stop warfarin, and give phytomenadione (vitamin K1) 0.5–1 mg for adults, 0.015– 0.030 mg/kg (15–30 micrograms/kg) for children by slow intravenous injection or 5 mg by mouth (for partial reversal of anticoagulation give smaller oral doses of phytomenadione e.g., 0.5–2.5 mg using the intravenous preparation orally); repeat dose of phytomenadione if INR still too high after 24 hours. Large doses of phytomenadione may completely reverse the effects of warfarin and make re-establishment of anticoagulation difficult.
• INR 6.0–8.0, no bleeding or minor bleeding—stop warfarin, restart when INR <5.0
• INR <6.0 but more than 0.5 units above target value—reduce dose or stop warfarin, restart when INR <5.0

For patients NOT on long-term anticoagulants without major haemorrhage Measure the INR (prothrombin time) at presentation and sequentially every 24–48 hours after ingestion depending on the initial dose and initial INR.
• If the INR remains normal for 24–48 hours and there is no evidence of bleeding, there should be no further monitoring necessary.
• Give vitamin K1 (phytomenadione) if: a) there is no active bleeding and the patient has ingested more than 0.25 mg/kg; OR b) the prothrombin time is already significantly prolonged (INR >4.0).
The adult dose of vitamin K1 is 10–20 mg orally (250 micrograms/kg body weight for a child).
Delay oral vitamin K1 at least 4 hours after any activated charcoal has been given. Repeat INR at 24 hours and consider further vitamin K1.