Calcium Unison Mechanism of Action

Pharmacology: Calcium is essential for the functional integrity of the nervous, muscular and skeletal systems. It plays a role in normal cardiac and renal function, respiration, blood coagulation and cell membrane and capillary permeability. Also, calcium helps to regulate the release and storage of neurotransmitters and hormone, the uptake and binding of amino acids, absorption of vitamin B12 and gastrin secretion. The major fraction (99%) of calcium is in the skeletal structure primarily as hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂; small amounts of calcium carbonates and amorphous calcium phosphates are also present. The calcium of bone is in a constant exchange with the calcium of plasma. Since the metabolic functions of calcium are essential for life, when there is a disturbance in the calcium balance because of dietary deficiency or other causes, the stores of calcium in bone may be depleted to fill the body's more acute needs. Therefore, on a chronic basis, normal mineralization of bone depends on adequate amounts of total body calcium.
Pharmacokinetics: Absorption: Approximately ¹/₅ to ¹/₃ of orally administered calcium is absorbed in the small intestine, depending on the presence of vitamin D metabolites, pH in lumen and on dietary factors eg, calcium binding to fiber or phytates. Calcium absorption is increased when a calcium deficiency is present or when a patient is on a low-calcium diet. In patients with achlorhydria or hypochlorhydria, calcium absorption, especially with the carbonate salt, may be reduced.
Protein-binding: Moderate, approximately 45% in plasma.
Elimination: Renal (20%): The amount excreted in the urine varies with degree of calcium absorption and whether there is excessive bone loss or failure of renal conservation. Fecal (80%): Consists mainly of non absorbed calcium, with only a small amount of endogenous fecal calcium excreted.