Bioavailability of fluoride in postmenopausal women: comparative study between sodium fluoride and disodium monofluorophosphate-calcium carbonate.

Fluoride (F) increases trabecular bone mass and can be used in the treatment of osteoporosis with crush fractures. As the bioavailability of sodium fluoride (NaF) can be impaired by concomitant absorption of calcium, both drugs have to be ingested separately. However, disodium monofluorophosphate-calcium carbonate (MFP-Ca), another F compound, allows a single administration. In a cross-over randomized study, we compared the bioavailability of both drugs under regular conditions of prescription. Ten postmenopausal women (aged 48-77 years) with glomerular filtration rate (GFR) greater than 70 ml/minute and without bone disease entered the study. Each received 25 mg of NaF [i.e., 11.3 mg F ion (F-)] fasting and 100 mg of Na2FPO3-1250 mg CaCO3 (i.e., 13.2 mg F-) with breakfast in a single dose separated by an 8-day washout. After dosing, plasma F levels and fractionated and total urinary F collection were determined during a 24-hour period using a specific electrode. Results show a significant shorter lag time absorption (Tmax = 1.4 +/- 0.2 hour) and a higher maximal concentration (Cmax = 260 +/- 60 ng/ml) for MFP-Ca than for NaF (Tmax = 2.5 +/- 0.4 hour; Cmax = 200 +/- 85 ng/ml). However, areas under curve (AUC) for MFP-Ca (1711 +/- 195 micrograms/liter/hour) and for NaF (1202 +/- 147 micrograms/liter/hour) were not significantly different. The relative bioavailability of both F compounds related to their fluoride content (i.e., 1.22 for AUC ratio) was equivalent, according to the Westlake method. These data provide the first evidence of comparable bioavailability of two F compounds in a population of postmenopausal women.(ABSTRACT TRUNCATED AT 250 WORDS)