RESUMEN
According to previous pharmacokinetic studies the bioavailability of fluorine (F) from sodium monofluorophosphate (MFP) doubles that of sodium fluoride (NaF). This paper reports a study designed to verify whether the vertebral bone mass increasing effect of NaF (30 mg F/day) was comparable to that of MFP (15 mg F/day), given for 18 months to osteoporotic postmenopausal women. The BMD of lumbar vertebrae of both groups showed significant increases (MFP: 60 +/- 15 mg/cm2, NaF: and 71 +/- 12 mg/cm2) over basal levels (P < 0.001). The difference between treatments was not significant (P = 0.532). The serum levels of ionic F (the mitogenic species on osteoblasts) were not related to the above mentioned effects. In NaF-treated patients, the fasting levels of total serum F increased significantly (6.7 +/- 0.9 microM vs. Basal: 2.0 +/- 0.8 microM; P < 0.001). This phenomenon was accounted for by ionic fluoride that increased over 20-fold (6.5 +/- 1.9 microM vs. Basal: 0.3 +/- 0.04 microM). In MFP-treated patients the fasting serum levels of total (7.0 +/- 0.7 microM vs. Basal: 2.2 +/- 0.9 M) and diffusible F (0.5 +/- 0.02 microM vs. Basal 0.2 +/- 0.02 microM) increased significantly (P < 0.001). The increase in the non diffusible F fraction is accounted for by protein-bound F, probably by the complexes formed between MFP and alpha 2-macroglobulin and C3. Serum diffusible F was formed by two fractions: ionic F and F bound to low molecular weight macromolecule/s (2,200 +/- 600 Da), in approximately equal amounts. The general information afforded by the present observations support the hypothesis that ionic F is released progressively during the metabolism of MFP bound to alpha 2-macroglobulin and C3. These phenomena explain why comparable effects to those obtained with 30 mg F/d of NaF could by obtained with one half the dose of MFP.