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 substanceMechanismPossible outcomeAction required
ACE inhibitorsReduced 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 effectSeparate doses by at least 2 hours
Antacids and products containing aluminium, calcium or magnesiumReduces iron absorptionReduced effect of ironSeparate doses by at least 2 hours
Ascorbic acidIncreases iron absorptionIncreased effects of ironBeneficial interaction possible — caution in haemochromatosis
Cholestyramineand colestipolIn vitro investigations have shown that cholestyramineand colestipol both bind iron citrateReduced effect of ironMonitor for iron efficacy if cholestyramine is being used concurrently

Separate doses by 4 hours. Increased iron intake may be required with long-term therapy

CimetidineIron can bind cimetidine in the gastrointestinal tract and reduce its absorptionReduced effect of iron and drugSeparate doses by at least 2 hours
Dairy products and eggsMay reduce iron absorptionReduced effect of ironMonitor for iron efficacy
ErythropoietinPharmacodynamic interactionAdditive pharmacological effect possibleBeneficial 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 ironReduced effect of ironMonitor for iron efficacy if these drugs are being used concurrently
HaloperidolMay cause decreased blood levels of ironReduced effect of ironMonitor for iron efficacy if these drugs are being used concurrently

Increased iron intake may be required with long-term therapy

L-dopa and carbidopaMay reduce bioavailability of carbidopa and L-dopaReduced drug effectSeparate doses by 2 hours
Omeprazole and other proton-pump inhibitorsReduced iron absorption due to changes in gastric pHReduced effect of ironMonitor for iron efficacy if omeprazole is being used concurrently
PenicillamineReduced drug and iron absorptionReduced drug and iron effectSeparate 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 absorptionReduced drug effectTake drug 2 hours before or 4-6 hours after iron dosing

Monitor patient for continued antibiotic efficacy

SulfasalazineMay bind together, decreasing the absorption of bothReduced drug and iron effectSeparate 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 absorptionReduced effect of ironMonitor 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 absorptionReduced drug effectMonitor for iron efficacy if tetracyclines are being used long term

Separate doses by 4 hours

L-thyroxineDecreased drug absorption possible. Iron supplements may decrease absorption of thyroid medication; however, iron deficiency may impair the body’s ability to make thyroid hormonesReduced drug effectThyroid function should be monitored and L-thyroxine dose may need alteration during treatment with iron

Separate doses by at least 2-4 hours

Vitamin AIron supplementation may cause a redistribution of retinol inducing vitamin A deficiency in infants with marginal vitamin A statusRedistribution of retinolIron supplementation in infants should be accompanied by measures to improve vitamin A status