The principal role of iron is to deliver oxygen to tissues. It binds with heme, the nonprotein portion of hemoglobin (Hgb), in the lungs and is distributed to tissues where it is also found as myoglobin. Cellular respiration, adenosine triphosphate storage using iron-coupling reactions, and possibly T-cell immunity and cognitive function actions are other roles that may require iron.

Absorption of iron usually takes place in the duodenum and occurs as the ferrous ion. Acidification with vitamin C is said to increase the bioavailability, whereas alkalinizers (e.g., antacid or basic ash foods, such as fruits and vegetables) may hinder absorption. Once absorbed, iron is then converted to ferric ion in the intestinal mucosal cells and binds to apoferritin, which forms ferritin (a storage protein said to regulate iron absorption). Transferrin binds iron and chromium in the plasma and transports iron to the liver, spleen, and bone marrow, where iron is again stored as ferritin. Iron is excreted principally in the feces.

Iron deficiency is associated with insufficient intake, excessive blood loss, achlo-rhydria, and malabsorption. Symptoms may include fatigue, dyspnea, palpitations, angina, tachycardia, and presentation of a hypochromic, microcytic anemia. Toxicity, namely hemosiderosis (mainly in males as a result of saturation of hemosiderin stores), can result from multiple blood transfusions, because blood contains about 0.5 mg iron/ml. In order to remain in iron balance, the daily iron intake of men, as well as of postmenopausal women, must be 0.5 to 1 mg. Because only 10% of iron will be absorbed, 10 times this requirement must be given orally as elemental iron. Although parenteral iron is 100% bioavailable, target site delivery, incorporation into the erythrocyte, takes at least 3 weeks. Menstruating women may require an additional 0.3 to 1 mg/d. The iron requirement is increased during pregnancy, due in particular to the increase in the total erythrocyte volume. This need is met partly by mobilization of iron reserves, which are restored postpartum when the total erythrocyte volume falls again. Parenteral iron may not need to be repleted during short periods of parenteral feeding if iron stores are adequate prior to the initiation of parenteral therapy. A test dose of 25 mg (0.5 ml of iron dextran) over 5 min will be needed, because there are reports of anaphylaxis. Sympathomimetics and anti-histaminics should be available if there is an adverse reaction. If the infusion is delivered peripherally, there will be less phlebitis if the vehicle is sodium chloride. A maximum daily dose of 100 mg is recommended, but total dose repletion is frequently infused over several hours. Patients with Crohn's disease may trap parenteral iron in the reticular endothelium with resultant adverse reactions, suggesting the possible undesirability of this dosage form in inflammatory states. Patients who are infected should not receive parenteral iron, because iron is typically sequestered to the liver during infective processes. When given intramuscularly, the product must be given via a Z-track technique; that is, the depression and lateral movement of the gluteal areas, upper, and outer quadrant, should ensure prevention of retrograde leak and staining of the subcutaneous fatty areas with iron.

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