Which dosage of ferrous sulfate is effective in the treatment of iron deficiency anemia?

Updated: Sep 07, 2019
  • Author: James L Harper, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Oral ferrous iron salts are the most economical and effective medication for the treatment of iron deficiency anemia. Of the various iron salts available, ferrous sulfate is the one most commonly used.

Although the traditional dosage of ferrous sulfate is 325 mg (65 mg of elemental iron) orally three times a day, lower doses (eg, 15-20 mg of elemental iron daily) may be as effective and cause fewer side effects. To promote absorption, patients should avoid tea and coffee and may take vitamin C (500 units) with the iron pill once daily. [18]

However, a study by Moretti et al suggests that the standard dosing of iron supplements may be counterproductive. Their research focuses on the role of hepcidin, which regulates systemic iron balance, partly in response to plasma iron levels. They found that when a large oral dose of iron is taken in the morning, the resulting increase in the plasma iron level stimulates an increase in hepcidin, which in turn will interfere with the absorption of an iron dose taken later in the day; indeed, suppression of iron absorption could last as long as 48 hours. [19, 20]

In one part of their study, twice-daily doses of 60 mg or greater resulted in an increase in serum hepcidin levels after the first dose and a 35-45% decrease in the amount of iron that was absorbed from the second dose. With increasing doses, study subjects showed an increase in the absolute amount of iron absorbed, but a decrease in the fraction of the dose that was absorbed. A six-fold increase in iron dose (from 40 mg to 240 mg) resulted in only a three-fold increase in iron absorbed. In another part of the study, total iron absorbed from a morning and an afternoon dose on one day plus a morning dose the next day was not significantly greater than absorption from two consecutive morning doses. [19]

Moretti et al concluded that providing lower dosages and avoiding twice-daily dosing will maximize fractional iron absorption. They note that although the short-term effects observed in their study will require confirmation in longer-term studies, their results support supplementation with 40-80 mg of iron taken every other day. A possible additional benefit of this schedule may be that improving absorption will reduce gastrointestinal exposure to unabsorbed iron and thereby reduce adverse effects from supplements. [19, 20]

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