Iron supplements are widely available, particularly in homes with small children and young women. The attractiveness of the bright color and sugar coating of the tablets and their initial distribution in non–child-resistant vials made children susceptible to ingestion. The 1997 Federal requirement that all iron-containing pharmaceuticals containing more than 30 milligrams of elemental iron be distributed only in blister packs reduced the reported incidence of iron ingestion and deaths in young children.1,2 This requirement was removed in 2003, but blister packs remain in common use along with child-resistant bottles, and serious iron poisonings in young children have remained low.2 Women of childbearing age are at risk for intentional iron overdose due to the availability of iron and increased stress during pregnancy and the postnatal period.3 Children with inadvertent overdoses4,5 and adults with intentional overdose6 are at risk of serious toxicity or death.
Total-body iron store averages about 4 grams in adults; the range is between 2 and 6 grams, with less iron in women than in men. About two thirds of the body's iron is incorporated into hemoglobin, and the remainder is found in other iron-containing proteins such as myoglobin, cytochromes, and other enzymes and cofactors, or is stored as ferritin. The recommended daily intake of iron is about 8 milligrams for boys, adult men, and nonmenstruating women; 18 milligrams for menstruating women; and 27 milligrams for pregnant females.7 Because excess iron is toxic, the body uses several mechanisms to maintain iron homeostasis: serum protein binding, intracellular storage, and, most importantly, regulation of GI tract absorption.8
The oral bioavailability of iron depends on the formulation ingested. Inorganic iron has <10% bioavailability, with ferrous iron (Fe2+) better absorbed than ferric iron (Fe3+). Common ionic formulations include ferrous chloride, ferrous fumarate, ferrous gluconate, ferrous lactate, and ferrous sulfate (Table 198-1). Nonionic formulations include carbonyl iron and iron polysaccharide (iron dextran). Most dietary iron is in the ferric form and chelated to the heme moiety. Following ingestion, the ferric ion is separated from heme and reduced to ferrous iron by a brush border ferrireductase. Chelated iron, such as that found in meat, is more readily absorbed than the iron in ionic preparations. Commercially available formulations of iron chelated with amino acids (e.g., glycinate) mimic the benefits of dietary meat for iron absorption (Table 198-1).
TABLE 198-1Iron Formulations and Elemental Iron Composition ||Download (.pdf) TABLE 198-1 Iron Formulations and Elemental Iron Composition
| ||Iron Formulation ||Elemental Iron Composition |
|Ionic ||Ferrous fumarate (PO) ||33% |
| ||Ferrous chloride (PO) ||28% |
| ||Ferrous sulfate (PO) ||20% |
| ||Ferrous lactate (PO) ||19% |
| ||Ferrous gluconate (PO) ||12% |
| ||Ferrous gluconate (IV) ||1.25% |
|Nonionic ||Carbonyl iron (PO) ||98% |
| ||Iron polysaccharide (PO) ||46% |
| ||Ferric hydroxide dextran (IV) ||10% or 20% |
| ||Iron sucrose (IV) ||2% |