Iron: Significant Interactions
Iron interacts with a variety of foods, herbs and drugs through several different mechanisms. Most commonly, the formation of insoluble complexes occurs whereby both iron and drug absorption is hindered. Separation of doses by several hours will often reduce the severity of this type of interaction. Additionally, substances that alter gastric pH have the theoretical ability to reduce iron absorption. A summary of interactions has been presented in table form for easy reference.
| Drug / therapeutic substance | Mechanism | Possible outcome | Action required |
| ACE inhibitors | Reduced absorption of ACE inhibitors. A small clinical trial found that concomitant iron administration reduced area-under-the-curve plasma levels of unconjugated captopril by 37% | Reduced drug effect | Separate doses by at least 2 hours |
| Antacids and products containing aluminium, calcium or magnesium | Reduces iron absorption | Reduced effect of iron | Separate doses by at least 2 hours |
| Ascorbic acid | Increases iron absorption | Increased effects of iron | Beneficial interaction possible — caution in haemochromatosis |
| Cholestyramineand colestipol | In vitro investigations have shown that cholestyramineand colestipol both bind iron citrate | Reduced effect of iron | Monitor for iron efficacy if cholestyramine is being used concurrently Separate doses by 4 hours. Increased iron intake may be required with long-term therapy |
| Cimetidine | Iron can bind cimetidine in the gastrointestinal tract and reduce its absorption | Reduced effect of iron and drug | Separate doses by at least 2 hours |
| Dairy products and eggs | May reduce iron absorption | Reduced effect of iron | Monitor for iron efficacy |
| Erythropoietin | Pharmacodynamic interaction | Additive pharmacological effect possible | Beneficial interaction possible |
| H2-receptor antagonists (antiulcer drugs) | Iron absorption is dependent upon gastric pH; therefore, medications that affect gastric pH may interfere with absorption of iron | Reduced effect of iron | Monitor for iron efficacy if these drugs are being used concurrently |
| Haloperidol | May cause decreased blood levels of iron | Reduced effect of iron | Monitor for iron efficacy if these drugs are being used concurrently Increased iron intake may be required with long-term therapy |
| L-dopa and carbidopa | May reduce bioavailability of carbidopa and L-dopa | Reduced drug effect | Separate doses by 2 hours |
| Omeprazole and other proton-pump inhibitors | Reduced iron absorption due to changes in gastric pH | Reduced effect of iron | Monitor for iron efficacy if omeprazole is being used concurrently |
| Penicillamine | Reduced drug and iron absorption | Reduced drug and iron effect | Separate doses by at least 2 hours Sudden withdrawal of iron during penicillamine use has been associated with penacillamine toxicity and kidney damage — caution |
| Quinolone antibiotics (e.g. norfloxacin) | Reduced drug absorption | Reduced drug effect | Take drug 2 hours before or 4-6 hours after iron dosing Monitor patient for continued antibiotic efficacy |
| Sulfasalazine | May bind together, decreasing the absorption of both | Reduced drug and iron effect | Separate doses by at least 2 hours |
| Tannins — herbs with significant tannin content (e.g. green tea, bilberry, raspberry leaf) | Tannin can bind to iron and reduce its absorption | Reduced effect of iron | Monitor for iron efficacy if these herbs are being used concurrently Separate doses by 2 hours |
| Tetracycline antibiotics (e.g. minocycline, doxycycline) | Reduced drug and iron absorption | Reduced drug effect | Monitor for iron efficacy if tetracyclines are being used long term Separate doses by 4 hours |
| L-thyroxine | Decreased drug absorption possible. Iron supplements may decrease absorption of thyroid medication; however, iron deficiency may impair the body’s ability to make thyroid hormones | Reduced drug effect | Thyroid function should be monitored and L-thyroxine dose may need alteration during treatment with iron Separate doses by at least 2-4 hours |
| Vitamin A | Iron supplementation may cause a redistribution of retinol inducing vitamin A deficiency in infants with marginal vitamin A status | Redistribution of retinol | Iron supplementation in infants should be accompanied by measures to improve vitamin A status |
