Little Johnny and Grandad’s warfarin

aka Toxicology Conundrum 015

Little Johnny is an inquisitive 15kg 3 year-old boy. His grandad was looking after him for the evening. About an hour ago, the phone rang just as grandad was about to take his evening warfarin tablets. Although he only turned his back for a second, there was enough time for little Johnny to start ploughing into the tablets…

Grandad usually has 6mg (2 x 3mg tablets) of warfarin in the evenings, but he is unsure how many tablets are missing. He thinks there “could be half a dozen” and says that “little Johnny loves taking pills”.


Questions

Q1. Is the history believable?

Answer and interpretation

I think so. It is normal behaviour for toddlers (aged 12-36 months) to explore their surroundings by putting things in their mouths. That is why this age group accounts for the majority of unintentional pediatric toxic ingestions.

If a poisoned child is outside this age group it is prudent to consider the possibility of “non accidental injury”. For instance, children younger than 12 months are not usually capable of self-administering agents.


Q2. What is the risk assessment?

Answer and interpretation

It is unusual for toddler’s to self-ingest more than 2 or 3 tablets at once. However, it pays to be cautious and consider the “worst case scenario”:

i.e. 6 x 3 mg = 18 mg warfarin (>1mg/kg)

Any time the “worst case scenario” suggests an ingestion of >0.5 mg/kg warfarin then there is the potential for clinically significant anticoagulation.


Q3. What signs and symptoms would you expect little Johnny to have?

Answer and interpretation

None! Based on this history little Johnny should be asymptomatic with no evidence of a bleeding diathesis.

Anticoagulation does not occur for about 8-12 hours after warfarin ingestion – and certainly not within 6 hours.


Q4. What is your management plan?

Answer and interpretation

Based on the risk assessment of the potential for clinically significant delayed anticoagulation, the following management plan is reasonable:

  • Administer Vitamin K 10mg po then discharge to care of the family with advice regarding medication safety.

Q5. When should little Johnny have a blood test?

Answer and interpretation

He doesn’t need any blood tests.

Small children who ingest warfarin >0.5 mg/kg do not require INRs or follow up if they are treated with 10mg vitamin K. This dose of vitamin will completely reverse the anticoagulative effects of warfarin.

There may be some exceptions to this rule:

  • delayed presentation (>6 hours)
  • patients with symptoms or signs of anticoagulation
  • possible massive ingestion (e.g. an older child with behavioural or developmental problems) – the threshold dose is poorly defined.

Q6. Would you administer activated charcoal?

Answer and interpretation

No.

Warfarin binds to activated charcoal, and absorption may be reduced if activated charcoal is given for decontamination within an hour of ingestion.

However, because vitamin K is such a safe and effective antidote, the benefits of decontamination are negligible and are outweighed by the risks (e.g. vomiting, aspiration). Furthermore, activated charcoal may impair the absorption of the orally administered antidote (vitamin K).


References
  • Baker RI, Coughlin PB, Gallus AS, Harper PL, Salem HH, Wood EM; Warfarin Reversal Consensus Group. Warfarin reversal: consensus guidelines, on behalf of the Australasian Society of Thrombosis and Haemostasis. Med J Aust. 2004 Nov 1;181(9):492-7. [PMID 15516194]

CLINICAL CASES

Toxicology Conundrum

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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