Iron overdose has been one of the leading causes of poisoning deaths in children younger than 6 years. Iron is used in pediatric or prenatal vitamin and mineral supplements and for treatment of anemia. Iron tablets are particularly tempting to young children because they look like candy.
Iron overload may develop chronically as well, especially in patients requiring multiple transfusions of red blood cells. This condition develops in patients with sickle cell disease, thalassemia, and myelodysplastic syndromes. 
For full discussion of iron toxicity in children, see Pediatric Iron Toxicity.
Iron toxicity can be classified as corrosive or cellular. Ingested iron can have an extremely corrosive effect on the gastrointestinal (GI) mucosa, which can manifest as nausea, vomiting, abdominal pain, hematemesis, and diarrhea; patients may become hypovolemic because of significant fluid and blood loss.
Cellular toxicity occurs with the absorption of excessive quantities of ingested iron. Severe overdose causes impaired oxidative phosphorylation and mitochondrial dysfunction, which can result in cellular death. The liver is one of the organs most affected by cellular iron toxicity, but other organs such as the heart, kidneys, lungs, and the hematologic systems also may be impaired. With chronic iron overload, the deposit of iron into the heart may cause death due to myocardial siderosis.
With both corrosive and cellular toxicity, the end result is significant metabolic acidosis, due to several factors. Hypoperfusion due to significant volume loss, vasodilatation, and negative inotropic effect of iron will result in lactic acidosis. Inhibition of oxidative phosphorylation will promote anaerobic metabolism.
Individuals demonstrate signs of GI toxicity after ingestion of more than 20 mg/kg. Moderate intoxication occurs when ingestion of elemental iron exceeds 40 mg/kg. Ingestions exceeding 60 mg/kg can cause severe toxicity and may be lethal. 
Suggested iron doses are based on calculation of the amount of elemental iron. Different iron preparations (salts) contain different amounts of elemental iron, as follows:
Fumarate - 33%
Sulfate - 20%
Gluconate - 12%
The 2014 Annual Report of the American Association of Poison Control Centers' (AAPCC) National Poison Data System reported 4024 single exposures to iron or iron salts, with one major outcome and one death. In addition, the AAPCC reported 11,180 single exposures to multiple vitamins containing iron, with one major outcome and no deaths. Overall, 75% of cases were in children younger than 6 years. 
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