The aluminum chloride salt that is formed in the reaction with gastric acid is insoluble and can cause constipation . Absorption of certain drugs, such as tetracycline , is inhibited by this antacid. Phosphate also may be rendered unabsorbable due to salt formation and cause a bone condition called osteomalacia. It is also used as an antidote to corrosive acid poisoning. It is fast reacting and only a small amount of ionic magnesium is absorbed into the blood stream.
Magnesium salts remain in the intestines and have a laxative effect.
Magnesium and aluminum containing antacids often combined to offset their individual effects on bowel function. Because it is readily soluble, it is rapidly removed from the gut by absorption. Therefore, sodium bicarbonate not useful for long term use as it can cause systemic alkalosis and fluid retention. Adverse reactions to antacids include changes in bowel habits such as flatulence, diarrhea, or constipation . Simethicone is included in some preparations to limit bloating and gas.