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The oral bioavailability of iron supplements

General | February 26, 2015 | Author: The Super Pharmacist


The oral bioavailability of iron supplements

Iron deficiency is the most common nutritional deficiency globally, leading to many individuals taking iron supplements. People may have low iron levels for a number of reasons, including:

  • An inability to absorb iron properly into the body  (this may occur due to disease of the bowel such as celiac disease, or if part of their stomach or small intestine has been removed)
  • Heavy menstrual bleeding
  • A lack of iron in food (particularly common in small children, pregnant women and teens)
  • Internal bleeding

This article discusses the oral bioavailability (the proportion of an unchanged drug that enters circulation into the body and has an active effect) of iron supplements.

How are iron supplements taken?

Iron is often taken orally as a first line treatment option in a number of pharmacological forms.

How are iron supplements taken?The most common form is iron (II) sulphate (also known as ferrous sulphate) and a wide range of other salts including gluconate and carbonyl iron. Vitamin C (ascorbic acid) may be included to aid better absorption of iron. 

When regular iron supplements such as ferrous fumarate are not tolerated or absorbed by individuals, Heme iron polypeptide is used, with a single study highlighting its ability to significantly increase serum iron levels.

Further studies are required to verify if these findings are replicated in a number of different experimental settings.

Side effects of taking iron supplements orally

Oral iron therapies are known to cause a number of adverse side effects including diarrhoea, constipation and abdominal cramping/pain. It has been evidenced that treatment with iron (II) sulphate results in more adverse side effects than iron (III)-hydroxide polymaltose complex or amino acid chelate.

Parenteral iron therapy

Parenteral iron therapy, administered either intravenously or intramuscularly, is often given as a secondary line treatment when oral therapies have failed or cannot be given for a particular reason. This may include:

  • Oral therapy producing severe side effects in patients that prevents their ongoing administration
  • Oral therapy is not a viable option i.e. the patient is unable to swallow
  • Immediate improvement in iron levels is required (such as before elective surgery)
  • Immediate improvement in haemoglobin levels are required (such as post operatively and post transfusion)
  • Patients with underlying medical conditions where oral administration is not tolerated (such as inflammatory bowel disease or renal patients)

There are some circumstances in which parenteral iron therapy cannot be given, such as the first trimester of pregnancy when an unacceptably high risk of harm to the unborn child is present. In general, parenteral therapy is not offered as a first line treatment as a result of its cost and invasive nature. It is preferred clinically for the treatment of certain medical conditions and is the preferred method of administration in some countries for patients who have chronic renal failure.

Side effects of taking iron supplements intravenously or intramuscularly

There are some rare allergic reactions associated with particular supplements. Iron sucrose has an allergy risk of 1 in 1000, with a recommended maximum dosage of 200mg three times a week to prevent adverse side effects.

Side effects of taking iron supplements intravenously or intramuscularlyMore commonly, many individuals who take iron supplements experience a change in their senses, with 1 in 10 patients experiencing an increasingly metallic taste in their mouths and/or when eating. To prevent accidental toxicity or overdose, chelating agents (capable of forming multiple bonds) are included in some iron supplements to remove the toxicity of free iron –the side effects of this action are diarrhoea and possible hematemesis (the vomiting of blood).

Oral bioavailability of Iron supplements

Non-heme iron supplements, when taken in conjunction with a number of other supplements, can decrease the efficacy and absorption of both the iron and other pharmacological solutions taken at the same time. As such, it is recommended that supplements taken with drugs such as quinolones, biophosphates and levodopa are all discussed with a family doctor or pharmacist to discuss any possible negative interactions or significant drops in efficacy.

Iron supplement with the most oral bioavailability

By definition, supplements that are administered intravenously have the highest rates of bioavailability. Medicines that are administered orally generally decrease in bioavailability as a result of incomplete absorption or first-pass metabolism (the process of a drug losing its efficacy before reaching systemic circulation and being able to have an effect on the patient). Many studies often compare oral and intravenous administration of iron therapy without directly considering its oral bioavailability, instead focusing on clinical outcomes and health benefits for patients.

A systematic review of a wide range of studies, published at the beginning of 2015, considered the role of oral iron supplementation in treating anaemia in older people. It found them to raise haemoglobin levels, but without any tangible health benefit.

The two main iron salts forms (ferric and ferrous irons) and common formulations (carbonyl iron, amino-acid chelates) are commonly used in practice. All dietary iron has to be reduced to the ferrous form in order to be active, and is absorbed three times more readily than its ferrous counterpart. The addition of Vitamin C to aid addition has been shown to be effective in increasing the active component of iron supplements. Taking iron supplements on an empty stomach has also been proven to improve their efficacy, with food decreasing absorption by an estimated 40-50%.  Australia’s best online discount chemist


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