<P> Iron therapy (intravenously or intramuscular) is given when therapy by mouth has failed (not tolerated by the patient), oral absorption is seriously compromised (by illnesses, or when the patient cannot swallow), benefit from oral therapy cannot be expected, or fast improvement is required (for example, prior to elective surgery). Parenteral therapy is more expensive than oral iron preparations and is not suitable during the first trimester of pregnancy . </P> <P> There are cases where parenteral iron is preferable over oral iron . These are cases where oral iron is not tolerated, where the haemoglobin needs to be increased quickly (e.g. post partum, post operatively, post transfusion), where there is an underlying inflammatory condition (e.g. inflammatory bowel disease) or renal patients, the benefits of parenteral iron far outweigh the risks . In many cases, use of intravenous iron such as ferric carboxymaltose has lower risks of adverse events than a blood transfusion and as long as the person is stable is a better alternative . Ultimately this always remains a clinical decision based on local guidelines, although National Guidelines are increasingly stipulating IV iron in certain groups of patients . </P> <P> Soluble iron salts have a significant risk of adverse effects and can cause toxicity due to damage to cellular macromolecules . Delivering iron parenterally has utilised various different molecules to limit this . This has included dextrans, sucrose, carboxymaltose and more recently Isomaltoside 1000 . </P> <P> One formulation of parenteral iron is iron dextran which covers the old high molecular weight (trade name DexFerrum) and the much safer low molecular iron dextrans (tradenames including Cosmofer and Infed). </P>

Where does the iron in iron supplements come from