Comparison of Iron Supplements

Comparison of Oral Iron Supplements

A new iron supplement product in the U.S. called Ferralet 90 is adding to the confusion surrounding the numerous oral iron supplements on the market. Ferralet 90 is a combination product containing carbonyl iron, B12, vitamin C, folic acid, and docusate and it is marketed as a prescription product. No oral iron dietary supplements are approved by the FDA, but manufacturers can choose to market their products as prescription only.8 There are two main iron salts forms (ferric and ferrous irons) and numerous formulations (e.g., amino-acid chelates, carbonyl iron, polysaccharide-iron complex, combination products, extended-release products, etc) available in the U.S. and Canada. All dietary iron has to be reduced to the ferrous form to enter the mucosal cells; therefore ferrous iron is absorbed three times more readily than the ferric form. Anecdotal claims that sustained-release iron preparations cause fewer gastrointestinal side effects have not been well substantiated.1,2 There is some evidence that controlled-release iron preparation causes less nausea and epigastric pain than conventional ferrous sulfate, but the discontinuation rates are similar.3 Theoretically, once-daily dosing can improve compliance. However, extended-release or enteric-coated formulations have been found to transport iron past the duodenum and proximal jejunum, thereby reducing the absorption of iron.1,2 Vitamin C is added to some products to enhance iron absorption. About 200 mg is needed to increase absorption of 30 mg of elemental iron.1 However, doses of 500 mg to 1000 mg only increase iron absorption by about 10%.2 Most iron preparations containing vitamin C don't have a sufficient amount of vitamin C to substantially affect iron absorption.1,2 In general, iron supplements should be taken on an empty stomach since food can decrease absorption by 40% to 50%. GI side effects such as nausea and abdominal pain occur more frequently as the quantity of soluble elemental iron in contact with the stomach and duodenum increases. Higher iron doses also increase the occurrence of constipation.1,10 Therefore, there should be no difference in GI tolerance when an equal quantity of elemental iron is administered regardless of the form of iron salt.2 A chart summarizing the differences among the various iron formulations is included.

There's confusion about the different oral iron products.

Many are promoted as better tolerated or absorbed...but not all of these claims can be substantiated.

Ferrous sulfate, ferrous gluconate, and ferrous fumarate contain different percentages of elemental iron. Efficacy and tolerability are similar for equal doses of elemental iron.

Carbonyl iron (Ferralet 90, Feosol Carbonyl Iron caplets, etc) is pure elemental iron that's absorbed slowly to reduce toxicity.
Prescribe these if you're concerned about accidental ingestion. Iron is still the #1 cause of pediatric fatalities due to toxicity.

Polysaccharide-iron complex (Niferex-150, etc) is iron bound to carbohydrates. It's promoted to improve tolerability, but there's no proof that there's a significant difference.

Heme iron polypeptide (Proferrin ES, etc) is derived from hemoglobin in animal red blood cells. It's better absorbed than the inorganic iron salts, especially when taken with food.

Use the inexpensive ferrous sulfate first-line...or carbonyl iron if toxicity is a concern.

Tell patients that GI tolerability is linked to the iron DOSE...not the salt. Enteric-coated and controlled-release preps might reduce nausea...but at the expense of lower absorption.

Vitamin C increases iron absorption, but most combo products don't contain enough. Over 200 mg is needed to increase absorption of 30 mg elemental iron.