2012 年 21 巻 3 号 p. 291-298
Calcium is an essential mineral, and its deficiency causes several diseases such as osteoporosis. The absolute bioavailability of calcium using modern pharmacokinetic methods has not been determined even though the relative bioavailability of calcium from various calcium salts has been examined using classic kinetics and pharmacokinetics. The serum calcium concentrations of three calcium salts, calcium chloride, calcium acetate and calcium ascorbate, were measured at various times after intravenous (i.v.) and oral administrations in mice, and the pharmacokinetic behaviors of the salts were investigated using a non-compartmental model. The degree of dissociation of the calcium salts was determined based on the extent of freezing-point depression. The pharmacokinetic parameters, MRT, Vdss, CLtot and AUC for i.v. administration of calcium at 15 and 30 mg/kg from three calcium salts indicated that all three may undergo similar mechanisms of calcium metabolism. The pharmacokinetic process was linear due to a first-order reaction. The pharmacokinetic parameters of calcium after oral administration at 150 mg/kg indicated that the calcium absorption was significantly different among the three calcium salts. The absolute calcium bioavailability of calcium ascorbate and calcium acetate was 2.6 and 1.5-fold, respectively, greater than that of calcium chloride. The mean residence time, MRTab, for absorption of calcium from calcium ascorbate was longer than those from calcium chloride and calcium acetate. Furthermore, it was estimated that calcium absorbed by passing through the intestinal membrane was the dissociated form because of higher degrees of apparent dissociation for the three salts. The calcium absorbability from calcium ascorbate via the intestinal track is significantly higher than those of calcium chloride and calcium acetate.
