Extracellular calcium – Therapeutic use
A calcium supplementation can be necessary when the diet does not supply a sufficient quantity, in particular during growth, pregnancy, breast feeding and ageing. It can decrease bone deterioration and prevent the risk of osteoporosis and its consequences. There are various pharmaceutical preparations containing calcium as essential active compound, for oral or injectable route.
The injectable forms are used to treat acute hypocalcemia.
The oral forms are intended for the prevention and the treatment of rickets and osteoporosis. Each dosage unit contains usually 500 mg of calcium mg in various forms, carbonate, gluconate, phosphate. There is little data concerning the bioavailability and the efficacy of each of these forms. Calcium carbonate in gastric acid medium gives calcium chloride which dissociates into ions Cl and Ca2+.
CO3Ca + 2 HCl  CO3H2 + Cl2Ca
At high-dose, calcium carbonate is prescribed for a particular indication, the treatment of the renal osteodystrophy characterized by hyperphosphatemy, hypocalcemia and hypersecretion of parathormone. Calcium intake raises calcemia and reduces the hypersecretion of parathormone.
Note: Calcium polystyrene-sulfonate is a resin exchanger of cations which, in the intestine, exchanges calcium against potassium for which it has more affinity. The polystyrene-sulfonate is used for the treatment of hyperkalemia
The adverse effects of a calcium supplementation are very reduced, except in the case of an unfortunate prescription during hypercalcemia, hypercalciuria with calciium lithiasis, prolonged immobilization during which calcemia and or calciuria rises. A calcium supplementation can reinforce the efficacy but also the toxicity of cardiac glycosides.
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