Pharmacologic Therapy Iron Deficiency Anemia

© The initial treatment of IDA is oral iron therapy with a goal of 200 mg of elemental iron daily for those who are able to tolerate the oral route. Many different iron products and salt forms are available. Table 66-3 lists the various salt forms of oral iron available, the amount of elemental iron in each product, and the approximate daily dose of the salt to attain 200 mg of elemental iron daily.

Iron supplementation resolves anemia by replacing iron stores in the body that are necessary for RBC production and maturation. If treated properly, a response (via the presence of reticulocytosis) should be seen in 7 to 10 days, and Hgb values should rise by about 1 g/dL (10 g/L or 0.62 mmol/L) per week. Patients should be reassessed if Hgb does not increase by 2 g/dL (20 g/L or 1.24 mmol/L) in 3 weeks.

Dosing for iron should be divided equally into two to three doses daily. An empty stomach (1 hour before or 2 hours after a meal) is preferred for maximal absorption. After absorption, iron binds to transferrin in the plasma and is transported to the muscles (for myoglobin), liver (for storage), or bone marrow (for red cell production). Iron is not actively excreted from the body but is "lost" through other measures already described. Some studies suggest that iron absorption may be increased by

adding ascorbic acid (vitamin C) to the drug regimen. However, administration of iron on an empty stomach and with ascorbic acid may increase the incidence of GI side effects, such as abdominal pain, nausea, and heartburn. Patients who cannot tol erate iron on an empty stomach can take it with food, but iron absorption is reduced when it is taken with food.

FIGURE 66-3. The anemia evaluation process. (ACD, anemia of chronic disease; MCV, mean corpuscular volume; Pb, lead; TIBC, total iron-binding capacity.)

Common toxicities associated with oral iron products include abdominal pain, nausea, heartburn, constipation, and dark stools. Drug interactions may occur with iron products, predominantly owing to iron-drug binding, resulting in decreased absorption of the interacting drug. Examples include fluoroquinolones, tetracyclines, and phenytoin. To avoid this interaction, doses of iron and the interacting drug should be separated by 2 to 4 hours.

Parenteral iron therapy may be appropriate in cases where patients are unable to tolerate the oral formulation because of toxicities or compliance. In addition, those who have IDA that has not responded to oral iron therapy (e.g., because of malabsorption) are also candidates for parenteral iron therapy.

Parenteral iron therapy currently is available in three different formulations, which are listed in Table 66-3. Iron dextran was the first parenteral iron formulation to be approved, followed by ferric gluconate, and then iron sucrose. Although these newer agents are only approved by the FDA to treat anemia associated with CKD in patients receiving EPO products, they are effective in treating IDA as well. Iron dextran is FDA approved for treating documented iron deficiency in patients who are unable to tolerate the oral formulation.

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