Warfarin Overdose

Treatment strategy for warfarin over-anticoagulation

If a patient has a high INR consider the following possible causes

  • New medication
  • Concomitant illness
  • Change in diet
  • Change in activity

An elevated INR can significantly increase the risk of death from haemorrhage

Smart Phone app

There is a smart phone app available to assist with managing over dose.

Patient has clinically significant bleeding

This intervention is designed to rapidly reverse the INR in what may be life-threatening circumstances. It is for any clinically significant bleeding where warfarin induced coagulopathy is considered a contributing factor.

Warfarin Vitamin K dose Prothrombinex-HT (PTX) or FFP Check INR Comments
Stop 5-10mg IV 25-50 IU/kg PTX plus 2 units of FFP if PTX not readily available 4 units FFP Assess patient continuously until both INR < 5.0 and bleeding stops. Contact on-call haematologist for more advice. The need to restart warfarin depends on the clinical picture.

Time to response:

15mins after PTX. 15mins after FFP. 4 hours after vitamin K but may take several hours to have full effect.

Notes

The current iv vitamin K preparation can be given as an iv push over 2-3 mins.
Prothrombinex-HT. Available from blood bank. Reconstitute with 20ml of water for injection. One 20ml vial=500units.
For INR < 5 use a dose close to 25Iu/kg, for an INR > 5.0 use a dose closer to 50IU/kg.
Administer at a rate of 3ml/min or as tolerated by the patient.
The INR can be measured within 15mins of dose completion and doses repeated as necessary depending on the INR. May offer advantage over FFP as a small volume and there is no time delay in thawing.

 

Patient with an INR above the therapeutic range with a high risk of bleeding

INR Warfarin Vitamin K dose Check INR Comments
< 5 Stop 1-2mg orally Next day Resume warfarin at a reduced dose once INR is in therapeutic range. If bleeding risk very high assess the need for continuing warfarin.
5-9 Stop 0.5-1mg IV or 1-2mg orally within 6-12 hours in practice normally next morning
> 9 Stop 1mg IV 6-12 hours early testing may be necessary if INR excessively above 9 or risk of bleeding assessed as very high.

 

This protocol gives relatively aggressive reversal of warfarin. If the INR falls significantly below the therapeutic range additional anticoagulant therapy should be considered for patients with a high risk of thrombosis.

Notes

The current IV vitamin K preparation can be given as an IV push over 2-3 mins.
Effects of INR from IV vitamin K seen within 4 hours, for oral vitamin K 12-24 hours.
Oral vitamin K dose: The injection solution can be given orally (the 10mg tablets is not readily divided into smaller doses). Konakion MM Paediatric® 2mg/ml solution is the only solution officially approved for oral use, but it should be noted that Konakion Adult injection® 10mg/ml ias an identical formulation.
An elevated INR can significantly increase the risk of death from haemorrhage

 

Patient with an INR above the therapeutic range with a low risk of bleeding

INR Warfarin Vitamin K dose Check INR Comment
< 5 withhold Nil within 1 to 2 days Can recommence warfarin at a reduced dose in 24-48 hours when INR in therapeutic range
5-9 withhold Nil within 24 hours. To check INR is not rising Resume warfarin at a reduced dose when the INR in the therapeutic range. May need to withhold warfarin for several days
> 9 withhold 1-2mg orally within 24 hours. Earlier if INR is excessively elevated