indication

For relief of heartburn and acid indigestion. May also be used as a nutritional supplement or to treat hypocalcemia.

pharmacology

Gastric-peptic disease occurs as a result of an imbalance between protective factors, such as mucus, bicarbonate, and prostaglandin secretion, and aggressive factors, such as hydrochloric acid, pepsin, and Helicobacter pylori (H. pylori). Antacids work by restoring acid-base balance, attenuating the pepsin activity and increasing bicarbonate and prostaglandin secretion. The acid-neutralizing capacity of calcium carbonate is 58 mEq/15 ml. When used as a nutritional supplement, calcium carbonate acts by directly increasing calcium stores within the body.

mechanism of action

Calcium carbonate is a basic inorganic salt that acts by neutralizing hydrochloric acid in gastric secretions. It also inhibits the action of pepsin by increasing the pH and via adsorption. Cytoprotective effects may occur through increases in bicarbonate ion (HCO₃^-) and prostaglandins. Neutralization of hydrochloric acid results in the formation of calcium chloride, carbon dioxide and water. Approximately 90% of calcium chloride is converted to insoluble calcium salts (e.g. calcium carbonate and calcium phosphate).

biotransformation

None.

absorption

Maximal absorption occurs at doses of 500 mg or less taken with food. Oral bioavailability depends on intestinal pH, the presence of food and dosage.

route of elimination

Excreted mainly in the feces. The majority of renally filtered calcium is reabsorbed in the ascending limb of the loop of Henle and the proximal and distal convoluted tubules. Also secreted by sweat glands.

drug interactions

Calcium Acetate: Calcium salts may enhance the adverse/toxic effect of calcium acetate. Concurrent use of other calcium salts with calcium acetate should be avoided when possible. This combination is particularly dangerous in patients with other risk factors for hypercalcemia, such as those with end-stage renal disease.

Calcium Chloride: Calcium salts may enhance the adverse/toxic effect of calcium chloride. Concurrent use of other calcium salts with calcium acetate should be avoided when possible. This combination is particularly dangerous in patients with other risk factors for hypercalcemia, such as those with end-stage renal disease.

Itraconazole: The antacid, calcium carbonate, may decrease the effect of itraconazole by decreasing its absorption.