Relative bioavailability of fluoride from monofluorophosphate tablets after single oral administration

The study was conducted on 12 healthy male Caucasian volunteers of an average age of 27.8 +/- 4.0 years with single oral doses of the following products: 1. sodium monofluorophosphate tablets (MFP-tablets, Mono-Tridin); 2. aqueous solution of 23.2 mg of sodium fluoride (NaF solution-reference); 3. aqueous solution of sodium monofluorophosphate (MFP solution). The three products were equivalent in fluorine content with 10.5 mg F. The bioavailability was evaluated on the basis of the plasma levels and of the urinary excretion of fluoride. The study was designed as a triple latin-square crossover and each subject received the three products in three different periods, at empty stomach. After administration of the products, fluoride appeared quickly in blood (lag time between 0.07 and 0.13 h) and invaded rapidly the blood (invasion t1/2 from 0.04 to 0.15 h). The Cmax of fluoride in plasma was 439 ng/ml at tmax of 1.08 h after MFP tablets, 430 ng/ml at a tmax of 0.51 h after NaF solution and 403 ng/ml at tmax of 0.62 h after MFP solution. The differences for the Cmax were not statistically significant. The relative bioavailability of fluoride from MFP tablets, estimated from the AUC, was 1.35, and significantly larger than that from the reference NaF solution. Fluoride was eliminated from plasma with an initial fast rate (t1/2 from 0.68 to 1.03 h) and a terminal slower rate (t1/2 from 4.71 to 7.37 h). The plasma levels of fluoride were consistent with a two-compartment open pharmacokinetic model after extravascular administration. In the 24 h following the administration the urinary excretion of fluoride accounted for 50-53% of the administered dose, without significant difference between the three products. The three products were well tolerated and no systemic or gastric adverse reaction was recorded.