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Calcium is a divalent cation that is essential to maintain the normal function of the heart, vascular smooth muscle, the skeletal system, the nervous system, and intracellular signaling. It is vital in enzymatic reactions, neurohormonal transmission, blood coagulation, and the maintenance of cellular integrity.12 The endocrine system maintains calcium homeostasis. Hypercalcemia raises the threshold for nerve and muscle excitation, resulting in muscle weakness, lethargy, cardiac conduction disturbances, and coma. Hypocalcemia can result in hyperreflexia, muscle spasms, tetany, seizures, and QT interval prolongation (Chaps. 12 and 15).12
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Sir Humphry Davy used his pioneering work in electrolysis to isolate potassium and sodium from their hydroxides in 1807. In 1808, using slightly moistened lime, Ca(OH)2, Davy succeeded again, in a series of experiments using electrolysis, to isolate calcium.25 Ringer performed controlled animal experiments in the 1880s demonstrating the importance of calcium in sustaining and resuscitating cardiac ventricular contraction.96,97 As the clinical use of calcium chloride antedated 1938, it was “grandfathered” under the Food, Drug, and Cosmetic Act; calcium gluconate was approved in 1941.37,115
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Chemistry/Preparation
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Calcium has an atomic number of 20, a molecular weight of 40.08 Da, and a valence of 2. For clinical use, calcium is prepared typically in combination with gluconate or chloride. Calcium as calcium chloride (CaCl2) is used in its dihydrate form CaCl2•2H2O, with a molecular weight of 147.02 Da when accounting for water. It is a white odorless fragments or granules that are freely soluble in water.1 Calcium as calcium gluconate is provided as calcium D-gluconate (1:2) monohydrate, C12H22CaO14•H2O, with a molecular weight of 448.39 Da.37 It is a clear and colorless to slightly yellow solution.
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Calcium as calcium chloride or gluconate is a component of electrolyte, parenteral nutrition, dialysis, and cardioplegic solutions.115 Calcium acetate is used orally to treat hyperphosphatemia, particularly in patients with end-stage kidney disease.10 Other oral calcium salts such as calcium carbonate, citrate, lactate, glubionate, glycerophosphate, and polycarbophil are variously used as cariostatics, food additives, mineral supplements, and stool stabilizers.
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Calcium is the fifth most abundant element and the most abundant mineral in the body, and the third most common plasma cation after sodium and potassium.1,31 More than 99% of the 1 to 2 kg of calcium in the adult human is located in bone.12 Calcium is variously reported in units of mg/dL, mmol/L (mM), and mEq/L, as well as both in total and ionized values. To convert mg/dL to mM, multiply by 0.25; to convert mg/dL to mEq/L, multiply by 0.5. Antidotal calcium is also variously ...