Felis ISSN 2398-2950

Iron toxicity

Synonym(s): Elemental iron toxicity

Contributor(s): Dawn Ruben, Patricia Talcott, Nicola Bates


  • Iron Iron is an essential mineral. When not protein bound in the body, it is highly reactive, induces free radicals and is damaging to tissues.
  • There are numerous forms of iron including:
    • Iron-containing supplements and multivitamins. Injectable iron therapy is also a potential source although this is rare in dogs and cats.
    • Some moss killers contain ferrous sulfate.
    • Some slug and snail killers contain ferric phosphate, generally 1% for domestic products and 3% for professional products. Iron (III) ethylenediaminetetraacetate is also used as a slug killer in some countries.
    • Oxygen absorbers or deoxidizer sachets used as preservatives in dried foods.
    • Iron-containing hand warmers and heat patches (for pain relief).
    • The remainder of this article will discuss toxicity from ingesting excessive amount of iron.
  • There are numerous forms of iron. The soluble forms are the most toxic. Insoluble forms, such as metallic iron or iron oxide (rust), are not considered toxic. Iron oxide and hydroxides (E172) are also used in some foods and medicines as a colorant.
  • Calculate the amount of elemental iron ingested to determine if the pet ingested a toxic amount of iron.
  • Mild to moderate iron toxicity can occur when 20-60 mg/kg of elemental iron is ingested. Severe toxicity can occur when over 60 mg/kg elemental iron is ingested. Over 100 mg/kg elemental iron is considered fatal without prompt treatment. Note these toxic doses are based on soluble, bioavailable forms of iron and will greatly overestimate the toxicity of insoluble poorly bioavailable iron compounds.

All cases of ingestion of iron tablets should be assessed urgently.



  • Toxicity occurs following ingestion of excessive amount of soluble iron, typically in the form of supplements or multivitamins or iron-containing gardening products.
  • Iron supplement usage is common in households with pregnant women or nursing mothers.

Predisposing factors


  • There are no specific predisposing factors. Any animal can become intoxicated by ingesting an excessive amount of iron.


  • Normally, the amount of iron that is absorbed from ingested food is determined by the bodys requirement for iron. Absorption of iron occurs in the mucosal cells of the small intestine through an active transport system. Absorbed iron is converted to ferric iron and then bound to the glycoprotein transferrin. Iron is then transported to the bone marrow and liver, where it is stored as hemosiderin and used as needed for oxygen transport by hemoglobin and myoglobin. There is no established mechanism for excreting bound iron.
  • When an excessive amount of iron is ingested, the transport mechanism becomes overwhelmed. Transferrin becomes saturated and the excess iron circulates in serum as free iron, which is corrosive and a strong oxidant. This free iron causes direct damage to epithelial cells, resulting in gastrointestinal mucosal necrosis and ulceration. Free iron will also damage mitochondria, resulting in hepatic necrosis.


  • Iron toxicity typically occurs in stages. The first stage occurs within 6 hours of ingestion. Free iron will damage the gastrointestinal mucosa, further increasing iron absorption. 6-24 hours following ingestion, the animal has an apparent recovery. Unfortunately, without treatment, about 12-96 hours following ingestion, diarrhea returns along with hepatic necrosis, coagulopathy, shock and possibly coma and death. Those that survive may develop gastrointestinal obstruction weeks later. GI mucosal damage and scar formation can result in stenosis and obstruction.


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Further Reading


Refereed papers

Other sources of information

  • Hall J D (2016) Iron. In: Blackwell's Five Minute Veterinary Consult. Smal Animal Toxicology. 2nd edn. Hovda L, Brutlag A, Poppenga R, Petersen K (eds) Wiley-Blackwell, Ames, Iowa. pp 707-715.
  • Hall J O (2013) Iron. In: Small Animal Toxicology. 3rd edn. Peterson M E, Talcott P A (eds). St Louis, Missouri: Elsevier. pp 595-600.
  • Albretsen J (2006) The toxicity of iron, an essential element. Vet Med 101 (2), 82-90 ResearchGate.
  • Plunkett S (2001) Emergency Procedures for the Small Animal Veterinarian. 2nd edn. Saunders. St. Louis. pp 341-343.
  • Gfeller R W & Messonnier S P (1998) Handbook of Small Animal Toxicology & Poisonings. Mosby. St. Louis. pp158-160.