Clinical Practice Guidelines

Iron poisoning

  • See also: General Management of Acute Poisoning Guideline

    Background

    Iron supplements are available in several different formulations. In iron poisoning, the important consideration is the amount of elemental iron ingested, not the amount of iron salt.

    Table: Iron medications

    Product per tablet Elemental iron per tablet
    FGF 250mg sulphate 80mg
    Fefol 270mg sulphate 87.4mg
    Ferrogradumet 325mg sulphate 105mg
    Ferro-tab 200mg fumarate 65.7mg
    Iron Melts 25.4mg fumarate 5mg
    Ferro-Liquid 30mg/mL sulphate  6mg/mL

    Percentage elemental iron

    Ferrous fumarate 33%, ferrous chloride 28%, ferrous sulfate 20%, ferrous gluconate 12%.

    Iron is also found in some plant fertilisers, eg sulphate of iron, and in some snail baits, eg iron phosphate.

    Assessment

    Patients requiring assessment

    • Ingestion of >40mg/kg elemental iron
    • Ingestion of an unknown quantity
    • Any symptomatic patients

    History and examination

    Initial symptoms:

    • Nausea, vomiting, diarrhoea, abdominal pain, hypotension, haematemesis, fever
    • Gastrointestinal symptoms related to the corrosive nature of iron may occur without systemic toxicity. The presence of any symptoms requires measurement of serum iron concentrations
    • Lack of symptoms within the first 6 hours makes significant toxicity unlikely

    Latent period:

    • In severe iron poisoning, there is often 6-24 hour latent period when initial symptoms resolve, before overt systemic toxicity declares
    • Thus improvement over this time may be a result of improvement or precede deterioration 

    Other symptoms:

    • Usually appear at 6-24 hours and last 12-24 hours
    • Tachycardia, vasoconstriction, hypotension and shock
    • Metabolic acidosis can occur
    • These are related to fluid shifts from intravascular to extravascular compartments and cellular hypoxia

    Multiple organ failure:

    • Occurs >48 hours after ingestion
    • Particularly hepatic failure

    Management

    ABC

    • Supportive therapy to maintain adequate blood pressure and electrolyte balance is essential
    • I.V. fluid resuscitation 20 mL/kg
    • Potassium and glucose administration as necessary

    Investigations

    Asymptomatic patients:

    • If tablet ingestion, do AXR. If AXR is negative, no further investigation or observation.
    • If unknown amount or >40mg/kg ingested, measure serum iron concentrations 4 hourly until falling.

    All symptomatic patients should have the following investigations:

    • AXR if tablet ingestion
    • ABG/CBG (acidosis)
    • Glucose (hyperglycaemia)
    • Serum iron
      • Usually peaks at 4-6 hours after ingestion.
      • Concentrations taken after 4-6 hours may underestimate toxicity because the iron may have either been distributed into tissues or be bound to ferritin.
      • In the case of slow release or enteric coated tablets, concentrations should be repeated at 6-8 hours as absorption may be erratic and delayed.
      • Once desferrioxamine is commenced, iron concentrations are not accurate at most labs using automated methods (including RCH)
    • FBE (leukocytosis)
    • U&E & Cr
    • X-match
    • Clotting (reversible early coagulopathy and late coagulopathy secondary to hepatic injury)
    • LFTs
    • If tablet ingestion, AXR may be helpful in evaluating gastrointestinal decontamination after whole bowel irrigation (WBI) (see below)

    Decontamination

    • Activated charcoal does not bind to iron and is not indicated
    • Decontamination of choice is WBI with nasogastric colonic lavage solution 30mL/kg/hr until rectal effluent clear (contraindicated if there are signs of bowel obstruction or haemorrhage)
    • WBI is indicated if the AXR reveals tablets or capsules ingested and more than 60mg/kg ingested. Speak to a toxicologist (131126) for advice before performing WBI

    Antidote

    • Desferrioxamine is a chelating agent that forms a water soluble desferrioxamine-iron complex
    • Speak to a toxicologist (131126) for advice before administering desferrioxamine
    • Consider desferrioxamine if:
      • Serum iron concentrations >90 micromol/L
      • Concentration 60 - 90 micromol/L and tablets visible on AXR or symptomatic (nausea, vomiting, diarrhoea, abdominal pain, haematemesis, fever)
      • The patient has significant symptoms of altered conscious state, hypotension, tachycardia, tachypnoea, or worsening symptoms irrespective of ingested dose or serum iron concentration
      • Do not wait for iron concentration if altered conscious state, shock, severe acidosis (pH <7.1), or worsening symptoms. If serum iron concentration is not readily available, a fall in serum bicarbonate concentration is a reasonable surrogate marker of systemic iron poisoning. Commence desferrioxamine without delay.
    • Dose: Desferrioxamine 15mg/kg/hr I.V. The rate is reduced after four to six hours so that the total intravenous dose in general does not exceed 80mg/kg/24 hours
    • Desferrioxamine-iron complex is renally excreted. If oliguria or anuria develop, peritoneal dialysis or haemodialysis may become necessary to remove ferrioxamine
    • It is difficult to determine the endpoint for chelation therapy. Significant poisoning usually requires administration for 12 -16 hours, however it is recommended to continue desferrioxamine until:
      • Patient is asymptomatic
      • Decontamination complete
      • Anion-gap acidosis resolved
      • Serum iron concentration <60 micromol/L
      • Desferrioxamine has been associated with pulmonary toxicity and should be used with caution if indications persist >24 hours
      • Discuss with a Clinical Toxicologist (131126)

    Disposition

    Discharge guidelines:

    • If <40mg/kg ingestion, and negative AXR if tablet ingestion, can discharge if asymptomatic 6 hours post ingestion 
    • If ingestion of >40mg/kg discharge only if remains asymptomatic and serum iron concentration falling and <60micromol/L on two measurements 4 hours apart
    • Remember in severe iron poisoning, there is often a 6-24 hour latent period when initial symptoms resolve, before overt systemic toxicity declares. Thus improvement over this time may be a result of improvement or precede deterioration
    • Consult ICU for patients being considered for desferrioxamine or with worsening symptoms