Pharmacokinetics of ingested fluoride: Lack of effect of chemical compound

Fluoride in drinking water may be present from natural sources or added as sodium fluoride (NaF), sodium silicofluoride (Na₂SiF₆) or fluorosilicic acid (H₂SiF₆). Results from an early study with rats suggested that, when ingested as Na₂SiF₆, the absorption and excretion of fluoride were greater than when ingested as NaF. Objective: The present single-blind, crossover study with 10 adults was done to determine three key pharmacokinetic parameters: the maximum plasma fluoride concentrations (C_max), the elapsed time to reach the maximum concentrations (T_max) and the 6-h areas under the time-plasma concentration curves (AUCs) after ingestion of 500 mL of water containing 0.67 or 5.45 mg F/L present naturally or added as NaF or H₂SiF₆. Design: Blood was collected prior to and at nine time points during 6 h after ingestion of the test solutions. Plasma was analysed by electrode after HMDS-facilitated diffusion and the data were analysed for statistically significant differences using repeated measures ANOVA. Results: The C_max, T_max and AUC values after ingestion of the solutions containing natural fluoride, NaF or H₂SiF₆ did not differ significantly at either dose level. Further, the T_max values associated with the 0.67 and 5.45 mg/L solutions did not differ significantly indicating that the absorption, distribution and elimination rates were not affected by the dose size. Conclusions: Considered together with published reports, the present findings support the conclusion that the major features of fluoride metabolism are not affected differently by the chemical compounds commonly used to fluoridate water nor are they affected by whether the fluoride is present naturally or added artificially.