Bioavailability and pharmacokinetic characteristics of two monofluorophosphate preparations with calcium supplement

Two studies on the rate and extent of bioavailability of fluoride from a single dose of oral preparations of sodium monofluorophosphate (Na2FPO3) combined with calcium supplement were conducted according to a cross-over design on 18 (Study 1) and 20 (Study 2) male healthy volunteers, respectively. Evaluated were: a) tablets containing 76 mg Na2FPO3 (Ref1); b) chewable tablets containing 76 mg Na2FPO3 and 1250 mg calcium carbonate (Test 1); c) effervescent tablets containing 76 mg Na2FPO and 3240 mg calcium lactogluconate/carbonate (Ref 2); d) effervescent tablets containing 76 mg Na2FPO3 and 1250 mg calcium carbonate (Test 2). In all preparations Na2FPO3 was equivalent to 10 mg elemental F. The calcium supplement was equivalent to 500 mg elemental Ca. Fluoride was assayed in serum and in urine by a gas chromatographic method with a limit of quantitation of 10 ng/ml. Test 1 was found equivalent to Ref1 with regard to rate and extent of bioavailability of fluoride in serum. Test 2 (effervescent tablets resulting in an oral solution of Na2FPO3 and calcium salts) was found bioequivalent in rate and extent to Ref2 (effervescent tablets authorized for marketing with the same content in F and Ca equivalents as Test 2). The pharmacokinetics of fluoride from all investigated preparations was characterized by a short lag time, a rapid absorption, a Cmax of fluoride of 291-351 ng/ml (without significant differences between preparations) reached 30-75 min after administration, and a terminal t1/2 of 6-14 h. About 50% of the absorbed fluoride was eliminated with the urine (from 0 to infinity time). The kur.el was 0.06 h-1. The renal clearance 65 ml/min. The preparations were well tolerated by the subjects. In conclusion, Test1 and Test2 represent combinations of Na2FPO3 with calcium supplement which are well tolerated and provide a rapid, reliable and practically complete bioavailability of fluoride. They are therefore suitable for the bone-forming therapy of osteoporosis.