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”.
Gastric decontamination for the whole family courtesy of ‘The Family Guy’…
Hands up who wants to give little Johnny some ipecac?
Questions
Q1. Is the history believable?
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?
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?
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?
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?
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?
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 et al. Warfarin reversal: consensus guidelines, on behalf of the Australasian Society of Thrombosis and Haemostasis. Medical Journal of Australia 2004; 181(9):492-487. [fulltext]
- Murray L, Daly FFS, Little M, and Cadogan M. Chapter 3.78 Warfarin; in Toxicology Handbook (2nd edition), Elsevier Australia, 2010.
- Murray L, Daly FFS, Little M, and Cadogan M. Chapter 4.29 Vitamin K; in Toxicology Handbook (2nd edition), Elsevier Australia, 2010.
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