Iron is used for the treatment of anemia and as a prenatal or daily mineral supplement. Owing to its wide availability as an over-the-counter nutritional supplement, it remains a common (and potentially fatal) ingestion. Introduction of blister packages and smaller dosages have led to an overall decline in iron poisonings. Currently, there are many iron preparations that contain various amounts of iron salts. Most children's preparations contain 10–18 mg of elemental iron per dose, and most adult preparations contain 60–90 mg of elemental iron per dose. The following description of the toxicity of iron relates to the ingestion of ferrous iron salts (eg, sulfate, gluconate, fumarate). Two elemental iron products, carbonyl iron and iron polysaccharide complex, have not been reported to produce the same toxicity as iron salts.
Toxicity results from direct corrosive effects and cellular toxicity.
Iron has a direct corrosive effect on mucosal tissue and may cause hemorrhagic necrosis and perforation. Fluid loss from the GI tract results in severe hypovolemia.
Absorbed iron, in excess of protein-binding capacity, causes cellular dysfunction and death, resulting in lactic acidosis and organ failure. Iron-induced reactive oxygen species cause oxidative and free radical injury and disrupt cellular process such as mitochondrial oxidative phosphorylation.
The acute lethal dose in animal studies is 150–200 mg/kg of elemental iron. The lowest reported lethal dose was in a 21-month-old child who was said to have ingested between 325 and 650 mg of elemental iron in the form of ferrous sulfate. Symptoms are unlikely if less than 20 mg/kg of elemental iron has been ingested. Doses of 20–30 mg/kg may produce self-limited vomiting, abdominal pain, and diarrhea. Ingestion of more than 40 mg/kg is considered potentially serious, and more than 60 mg/kg is potentially lethal. Even though they contain iron salts, there are no reported cases of serious or fatal poisoning from the ingestion of children's chewable vitamins with iron. The reason for this is likely from its lower iron per tablet dosage than typical iron supplements.
Iron poisoning is usually described in five stages. However, clinical manifestations may overlap and patients do not necessarily pass through the same temporal stages.
First stage. Shortly after ingestion, the corrosive effects of iron cause abdominal pain, vomiting, and diarrhea, often bloody. Massive fluid or blood loss into the GI tract may cause serious hemodynamic instability. Absence of GI symptoms within the first 6 hours of ingestion essentially excludes serious iron toxicity.
Second stage. Patients who pass the first stage may experience a latent period of apparent GI improvement over 6–24 hours. However, ongoing cellular toxicities still occur and patients continue to demonstrate tachycardia and lethargy along with evidence of metabolic acidosis.
Third stage. This may occur within the first few hours of massive ingestion or 12–24 hours ...