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Description of key information

The bioavailability of fluoride was investigated in human volunteers.
Maternal -foetal transfer of fluoride in pregnant women
Metabolism of fluorides in man
Gastrointestinal absorption of fluorides in humans

Additional information

In spite of the moderate dissolution of the calcium fluoride tablets seen in vitro in simulated gastric fluid, no absorption of fluoride was apparent in human volunteers as measured by plasma levels; values at all time points were circa 20 ng/mL plasma. In contrast, a marked elevation of plasma fluoride levels (circa 5 -6 times pre-dosing levels) to circa 100 -120 ng/mL plasma was seen in the volunteers administered sodium fluoride.

The absorption of fluoride was investigated in pregnant female volunteers administered calcium fluoride or sodium fluoride supplements. Elevated maternal fluoride levels were seen in all treated groups and were comparable following supplementation with sodium fluoride or calcium fluoride. In all groups, umbilical cord fluoride levels were consistently slightly higher than maternal levels. The study shows a comparable bioavailability of sodium fluoride and calcium fluoride. The absorption of fluoride from the gastrointestinal tract is reported to be remarkably effective, with nearly complete absorption of sodium and calcium fluoride in solution (96 -97%) and lower absorption from solid calcium fluoride (62%). Approximately half of the absorbed fluoride is excreted and half retained in the skeleton. Evidence suggests that excretion is urinary, with the small proportion of orally administered fluoride excreted in faeces representing the unabsorbed fraction. The excretion of fluoride in sweat may also be significant.

The bioavailability of fluoride administered in different forms (calcium fluoride and sodium fluoride) was investigated in groups administered sodium fluoride. Serum levels increased rapidly from background to peak at 0.341 ppm at 30 minutes. Levels subsequently dropped gradually to reach background at 24 hours. Urinary excretion over 24 hours accounted for 48.1% of the administered fluoride.

In the group administered calcium fluoride, serum fluoride levels were slightly raised after one hour and reached a peak concentration of 0.073 ppm at two hours. Individual serum fluoride values were much more variable than in the other group. Urinary excretion over 24 hours accounted for 8.5% of the administered fluoride. The gastrointestinal absorption of fluoride is influenced by the solubility of the form in which it is administered.