Absolute bioavailability of fluoride from disodium monofluorophosphate and enteric-coated sodium fluoride tablets

The absolute bioavailability and other pharmacokinetic parameters of two fluoride formulations were investigated in 13 healthy volunteers, aged 61-70 years.

The following formulations were administered, under fasting conditions, in a single-dose three-way cross-over design: tablets of 76 mg disodium monofluoro phosphate (MFP, equivalent to 10.0 mg F- ion), enteric-coated (e.c.) tablets of 25 mg sodium fluoride (NaFor, equivalent of 11.3 mg F- ion), and an isoosmotic aqueous injection solution (4 ml) of 22.1 mg sodium fluoride (NaFiv, equivalent of 10.0 mg F- ion). There was a wash-out period of at least one week between each administration. Blood was sampled before and during a 24-hour period after administration. For F- excretion urine was sampled 48 hours before (baseline) and over the 48 hours after the administration.

The mean t1/2 values of the three formulations were 8.3, 8.7 and 8.3 h for MFP, NaFor and NaFiv respectively, and were not significant different. Mean Cmax after MFP was significantly higher than after NaFor [344 vs 142 micrograms.l-1]. Mean tmax for MFP was shorter than for NaFor [1.1 vs 4.6 h]. MFP had significantly higher bioavailability [102.8%] than NaFor [64.2%].

The MFP formulation showed higher bioavailability with smaller variation than the NaFor formulation. MFP is preferable, therefore, for fluoride therapy in clinical practice, and changing from NaFor to MFP will require adjustment of the dose.