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Iron salts are not well absorbed by mouth, and food may further impair their absorption.
Compounds containing calcium and magnesium, including antacids and mineral supplements, and bicarbonates, carbonates, oxalates, or phosphates, may impair the absorption of iron by the formation of insoluble complexes. Similarly, the absorption of both iron salts and tetracyclines is diminished when taken together orally. If treatment with both drugs is required, a time interval of about 2 to 3 hours should be allowed between them. A suitable interval is also advised if an iron supplement is needed in patients given trientine. Zinc salts may decrease the absorption of iron. Iron is chelated by acetohydroxamic acid, reducing the absorption of both. Iron should not be given with dimercaprol as toxic complexes may form.
The response to iron may be delayed in patients receiving systemic chloramphenicol.
Some agents, such as ascorbic acid and citric acid, may actually increase the absorption of iron.
In addition to those already mentioned, iron salts can also decrease the absorption of other drugs and thus reduce their bioavailability and clinical effect. Drugs affected include cefdinir, bisphosphonates, entacapone, fluoroquinolones, levodopa, methyldopa, mycophenolate mofetil, and penicillamine.
