Thursday, 2 June 2016

Iron Overdose

Iron overdose is common, but it is infrequent that it causes severe problems. I have seen it frequently in children, who take their parents well woman tablets, or similar.

Background
When thinking about iron, the first thing that must be done is to convert the amount of iron taken, to the amount of elemental iron ingested. This varies considerably between different types of iron tablets, depending on the type of ferrous or ferric salt:

  ferrous sulfate (dried) — divide dose by 3.3
  ferrous sulfate (heptahydrate) — divide dose by 5
  ferrous gluconate — divide dose by 9
  ferrous fumarate — divide dose by 3
  ferric chloride — divide dose by 3.5
  ferrous chloride — divide dose by 4

You can then risk stratify, by the amount of elemental iron they have ingested:
  <20mg/kg –– asymptomatic
  20-60mg/kg –– GI symptoms only
  60-120mg/kg –– potential for systemic toxicity
  >120mg/kg –– potentially lethal

Peak serum iron levels occur 4-6 hours following iron ingestion, then levels fall due to intracellular shift. Levels do not clearly correlate with clinical toxicity, but > 90 micromol/L (500 mcg/dL) is generally considered predictive of systemic toxicity (equivalent to >60mg/kg)

Pathophysiology
Local Effects - corrosive injury to the GI mucosa (vomiting, diarrhoea, haematemeis, melaena) . Can lead to gastric strictures.

Systemic Effects - cellular toxin, targeting the cardiovascular syndrome. Severe lactic acidosis from hypoperfusion due to volume loss, vasodilation and negative inotropic effects.


Clinical Symptoms


Investigations
Blood gas - can look like DKA. Anion gap metabolic acidosis.
BMs - can be hyperglycaemic
AXR
LFTs, Coags — hepatic failure
U&E — renal failure
Iron levels

Management
**Not adsorbed by activated charcoal**
Whole bowel irrigation for ingestion >60mg/kg
Surgical or endoscopy removal if >120mg/kg or WBI not feasible

Desferroxamine Chelation:
    level >90 micromol/L at 4-6 hours post-ingestion
    evidence of systemic toxicity
    shock
    metabolic acidosis
    altered mental status

Chelates free irons that can be renally excreted. Ferrioxamine is then excreted unchanged in the urine which classically, not reliably, turns a vin rose colour.

15 mg/kg/h, reduced if hypotension occurs, may be titrated up to 40mg/kg/h in severe toxicity
cardiac monitoring is mandatory. Can cause hypersensitivity, ARDS, toxic retinopathy or yersinia sepsis. Can be stopped when the patient is stable and serum iron is <60micromol/L - usually 56 hours.



References
http://learning.bmj.com/learning/modules/elucidat/57067260702df.html?moduleId=10055999&status=LIVE&action=start&_flowId=ELU&sessionTimeoutInMin=90&locale=en_GB&shouldStartAtQuestionSection=false

https://www.aliem.com/2014/management-iron-toxicity/
http://lifeinthefastlane.com/ccc/iron-overdose/
http://lifeinthefastlane.com/toxicology-conundrum-034/
https://wikem.org/wiki/Iron_toxicity
http://lifeinthefastlane.com/tox-library/antidote/desferrioxamine/
http://www.foamem.com/2014/08/06/management-of-iron-toxicity/
http://adc.bmj.com/content/87/5/400.full 
http://lifeinthefastlane.com/cicm-saq-2009-2-q18/ 




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