IRON OVERDOSE
Intervention criteria
Ingested dose
< 10 – 20 mg/kg
20 – 60 mg/kg
0 – 120 mg/kg
> 120 mg/kg
non – toxic
potentially toxic
toxic, but fatal outcome unlikely
potentially fatal
Example:
Note that elemental quantity of iron in tablets needs calculation
5 x Fergon tablets (300 mg ferrous gluconate) ingested by a 10 kg toddler.
5 x 300 mg/10 kg = 150 mg/kg
In fact only 11% (33 mg) of tablet is elemental iron. Therefore
5 x 33 mg/10 kg = 16.5 mg/kg
Toxic Mechanisms
1.
Direct corrosive effect on the GIT
2.
Metabolic acidosis
a. Conversion of Fe++ to Fe+++, binding to -OH and release of H+
b. Inhibition of mitochondrial respiration and lactic acid production
c. Decreased CO, vasodilation, decreased peripheral perfusion and
anoxia
d. Hypovolaemia secondary to; vomiting, diarrhoea, and GIT
haemorrhage and third spacing
e. Hepatic failure
3.
Cell death following lipid peroxidation due to production of free radicals
4.
Coagulopathy
a. Initially due to direct iron inhibition of thrombin, then;
b. Secondary to hepatotoxicity and reduced production of factors II, VII,
IX and X
Phases of intoxication
1.
Acute GIT (0.5 – 6 hours) - Nausea, vomiting, diarrhoea, corrosion,
haematemesis
2.
Latent (6 – 24 hours) – Asymptomatic period
3.
Metabolic acidosis/multiorgan failure
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4.
GIT stricture formation (6 – 8 weeks)
Investigations
Serum Iron Level
Take four hours (2 – 6 hours) after overdose and repeat at 6 – 8 hours if sustained
release formulation of iron ingested. Will be falsely low in presence of
desferrioxamine.
10 – 30 mcmol/l
30 – 60 mcmol/l
60 – 90 mcmol/l
> 90 mcmol/l
normal range
significant toxicity unlikely
possible toxicity/symptomatic patients should be treated
treat regardless of clinical state
If significant ingestion
ABG
Glucose
INR
U&E’s
FBC
Invasive blood pressure monitoring
X-ray - to ensure adequate decontamination
Management
1.
Decontamination
Iron is well known to form drug concretions (pharmacobezoar) and/or become
adherent to the gastric wall due to its corrosive effect. Activated charcoal is not
effective.
a. whole bowel irrigation
b. gastroscopic removal
c. gastrotomy
X-ray review following decontamination procedures should be performed to ensure
removal of drug from the GIT.
2.
Antidote
Desferrioxamine
15mg/kg/hour - up to 80mg/kg/day in first day…
Continue treatment until serum iron ≤ 60 mcmol/l, patient asymptomatic and urine
colour is no longer “vin rosé” (ensure no iron remains in the gut).
Note:
a. hypotension following rapid infusion (?anaphylactoid reaction)
b. renal failure occur if patient hypovolaemic
c. prolonged (greater than 24 hour) infusions associated with ARDS
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d. interference with serum iron measurement (spurious reduction)
e. pre-disposes patient to Yersinia enterocolitica infection
3.
Supportive care
a. aggressive fluid replacement
b. correction of acidosis (sodium bicarbonate)
c. correction of coagulation disorders (fresh frozen plasma)
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