[Fluoride bioavailability from sodium fluoride alone or in association with different calcium salts]

Fluoride pharmacokinetics were studied in twelve healthy subjects after oral administration of one tablet of osteofluor-containing 25 mg of sodium fluoride alone or associated with different calcium salts (500 mg Ca element) given as microcrystalline hydroxyapatite compound or powdered tri-calcium phosphate. Fluoride was measured in plasma and urine with a specific electrode and fluoride bioavailability from the three drugs was compared. Calcium absorption after oral load was assessed by measuring variations from the fasting state of plasma calcium and parathyroid hormone and of the urinary calcium to creatinine ratio. The bioavailability of fluoride is significantly decreased by the association to sodium fluoride of hydroxyapatite but not of tri-calcium phosphate. Calcium absorption seems greater after administration of hydroxyapatite compound. The decrease of the fluoride bioavailability is probably dependent on the capacity of calcium absorption from the calcium salts. The association of calcium to fluoride is absolutely required for treatment of osteoporosis. The microcrystalline hydroxyapatite compound seems preferable in view of its greater calcium absorption and of its limited decrease in fluoride bioavailability.