Calcium carbonate drug interactions

Drug/Food interactions Administration of iron with food decreases the iron absorption by at least 50%. Administration of calcium and iron supplements with food can reduce ferrous sulfate absorption by 33%. If combined iron and calcium supplementation is required, iron absorption is not decreased if calcium carbonate is used and the supplements are taken between meals. 

Excipients may interact directly with the drug to form a water-soluble or water-insoluble complex. If tetracycline is formulated with calcium carbonate, an insoluble complex of calcium tetracycline is formed that has a slow rate of dissolution and poor absorption. 

Drug Interactions Various drugs can decrease T absorption. Drugs such as aluminum hydroxide, ferrous sulfate, sucralfate, and calcium carbonate should be separated from T administration by 1 to 2 hours. Bile acid sequestrants (cholestyramine and colestipol) must be separated from T by at least 4 hours and preferably 6 hours. CYP450 enzyme inducing drugs such as phenytoin, carba-mazepine, rifampin, and phenobarbital can increase T requirements. 

Information about the interactions with calcium carbonate is more limited than with the aluminium/magnesium antacids, but Table 10.3 , (p.329) shows that the bioavailabilities of ciprofloxacin and norfloxacin, and to a lesser extent gemifloxacin, can be reduced. These reductions are less than those seen with the aluminium/magnesium antacids, but using ciprofloxacin as a guide a very broad rule-of-thumb would be to separate the drug administration by about 2 hours to minimise this interaction. This is clearly not necessary with levofloxacin, lomefloxacin, moxifloxacin or ofloxacin, nor probably with some of the other qui-... 

Calcium, also found in both dairy foods and some supplements, has several food and drug interactions. Like iron, calcium is only absorbed in ionic form. It too requires an acidic environment for optimal absorption, particularly when it is in the calcium carbonate form. This form is best taken with meals. Unlike iron, more calcium is absorbed in the parts of the small intestine located farthest from the acidic stomach. As a result, acid blocking medications are not as detrimental to absorption as they are for iron. 

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