Chemical stability and mode of gastrointestinal absorption of sodium monofluorophosphate.

Sodium monofluorophosphate, an agent used for the fluorine therapy of osteoporosis, is chemically stable in aqueous environment in the range from pH 13 to 2. At pH lower than 1.5 the monofluorophosphate ion (MFP) hydrolyzes to fluoride and orthophosphate. At these pH values fluoride forms undissociated hydrofluoric acid which damages the gastric mucosa. Therefore, to prevent the formation of hydrofluoric acid, sodium monofluorophosphate should always be combined with buffering agents, preferably calcium salts, because calcium is compatible with MFP and is an aid for osteoporosis. MFP is stable in the intestinal environment. It is absorbed from the gastrointestinal lumen and is then hydrolyzed into fluoride and orthophosphate. Hydrolysis is provided by MFPases of the intestinal mucosa and of the liver. Alkaline phosphatase has MFPase activity, whereas acid phosphatase has not. In conclusion, if buffered with an appropriate calcium salt, MFP is stable in the gastrointestinal environment and does not release fluoride which could damage the gastrointestinal mucosa and be sequestrated by calcium ions of the diet or given as medicaments.