Calcium Carbonate and Ferrous Supplement Interactions

Interaction:

• The bioavailability of orally administered iron may be reduced by concomitant administration of antacids or other agents with acid-neutralizing effects. 
• The exact mechanism is unknown but may involve reduced iron solubility due to increase in gastric pH and/or reduced absorption due to complexation or precipitation of the iron. 
• Based on existing data, sodium bicarbonate and calcium carbonate appear to have greater effects than antacids containing magnesium and aluminum hydroxides. 
• In a study of patients with mild iron deficiency anemia, coadministration of ferrous sulfate with sodium bicarbonate 1 gram and calcium carbonate 500 mg reduced iron absorption by 50% and 67%, respectively, while 5 mL of an antacid containing magnesium and aluminum hydroxides had little effect
• Calcium decreases absorption of oral iron tablets by 30-40%

Management:

• To minimize the potential for interaction, it may be appropriate to administer oral iron preparations at least two hours apart from antacids or other agents with acid-neutralizing effects

Dietary Consideration

• Calcium absorption from calcium carbonate is increased 10% to 30% by administering with a meal. 
• However, patients on very large doses of calcium to treat/prevent hypocalcemia (e.g. post-parathyroidectomy) may be prescribed calcium carbonate both with AND in between meals

References:

1. http://www.drugs.com/drug-interactions/calcium-600-d-with-ferrous-fumarate-2917-13737-1077-0.html?professional=1
2. http://www.kidneyhealth.ca/wp/wp-content/uploads/pdfs/P&P/P&P_medadmintimes