iron supplements

Last edited 03/2022 and last reviewed 03/2022

The idea behind iron supplements is to correct the anaemia and to replenish body iron stores (1).

• ferrous are better absorbed than ferric salts.
• replacement of iron pharmacologically requires between 120 and 180 mg of elemental iron per day.

The most commonly used preparation is ferrous sulphate, 200mg tds (= 65mg x 3 of elemental iron/day) (2)

• patients who do not tolerate traditional doses, a lower dose may be as effective and better tolerated
• other iron compounds such as ferrous fumarate 200mg tds (= 65mg of iron tds), ferrous gluconate or formulations (iron suspensions) can also be used and may be tolerate better than  ferrous sulphate (1)

A rise in haemoglobin concentration of around 0.1 g/dL per day (about 2 g/dL every 3 weeks) indicates effective treatment (but may vary from patient to patient) (2). Confirm treatment response by repeating haemoglobin levels at 2-4 weeks after starting iron supplements. If the response is

• inadequate - could be due to a problem with adherence, malabsorption, or continuing blood loss, consider further investigations (1,4)
• adequate - ensure that the haemoglobin level has returned to normal by a repeat blood count at 2–4 months (3)  

Oral iron should be continued for 3 months even after the iron deficiency has been corrected so that stores are replenished (1).

In patients who fails to respond to iron therapy or ones who are intolerant, the following parenteral preparations could be used:

• iron sucrose - administered intravenously
• ferric carboxymaltose - administered intravenously
• iron (III) hydroxide dextran - administered either intravenously or by deep gluteal intramuscular injection

Anaphylaxis rates with IV iron therapy:

• a study revealed that the adjusted incidence rates (IRs) for anaphylaxis per 10,000 first administrations were 9.8 cases (95% CI, 6.2 to 15.3 cases) for iron dextran, 4.0 cases (CI, 2.5 to 6.6 cases) for ferumoxytol, 1.5 cases (CI, 0.3 to 6.6 cases) for ferric gluconate, 1.2 cases (CI, 0.6 to 2.5 cases) for iron sucrose, and 0.8 cases (CI, 0.3 to 2.6 cases) for ferric carboxymaltose (5):
  • study authors concluded:
    • rates of anaphylaxis were very low with all IV iron products but were 3- to 8-fold greater for iron dextran and ferumoxytol than for iron sucrose

Reference:

• (1) Goddard AF et al. Guidelines for the management of iron deficiency anaemia. Gut. 2011;60(10):1309-16.  
• (2) Provan D. (2010). Iron deficiency anaemia. ABC of clinical haematology  
• (3) Smellie WS et al. Best practice in primary care pathology: review 3. J Clin Pathol. 2006;59(8):781-9. 
• (4) Todd T, Caroe T. Newly diagnosed iron deficiency anaemia in a premenopausal woman. BMJ. 2007;334(7587):259
• (5) Chintan V. Dave, Gary M. Brittenham, Jeffrey L. Carson, et al. Risks for Anaphylaxis With Intravenous Iron Formulations: A Retrospective Cohort Study. Ann Intern Med. [Epub ahead of print 29 March 2022]. doi:10.7326/M21-4009