Fluoride bioavailability after intravenous and oral administration: Importance of renal clearance and urine flow

Abstract

Fluoride (3 mg) was administered as a continous intravenous infusion during 30 min to 6 healthy subjects. Plasma concentrations and urinary excretion of fluoride in these experiments were compared with those obtained following oral administration of 2.82 mg, 4.50 mg, 5.64 mg, and 9.40 mg in the form of tablets and capsules. There were large day-to-day variations in the renal clearance of fluoride. This was shown to be due to differences in the urinary flow, an increase in flow causing an increase in renal clearance. The mean value of renal clearance from all experiments was 66.2 +/- 27.8 (SD; n = 16) ml/min. The extrarenal clearance, suggested to represent mainly the clearance to the bone pool, showed less interindividual variation: mean 110.3 +/- 32.3 (SD; n = 6) ml/min; the fraction remaining in the bone pool was highly consistent: 0.579 +/- 0.049 (SD; n = 6). When apparrent bioavailability was calculated from plasma and from urinary data, there was a great intra- and intersubject variation, as well as poor agreement between the two methods of calculations. This was found to be due to the day-to-day variation in renal clearance, which, in turn, varied with urinary flow. By use of equations that corrected for these variations, it was found that the bioavailability of sodium fluoride tablets is approximately 100%.

In vitro and in vivo assessment of a glass slow fluoride releasing device: a pilot study

“…22 It was also of interest that the experiment showed that there was no rapid dissolution of the glass in the acidic environment of the stomach. The plasma peak levels achieved and the timing of the peak after ingestion of the NaF tablet are very similar to those reported by Trautner and Einwag 23 and also of Ekstrand et al 24 This was also shown in the animal experiments carried out by Mirth et al 5 with the copolymer membrane slow F releasing device, where there was no change in blood plasma F and no signs of toxicity. The conclusion to be drawn from this initial study was that should a glass pellet break or fall off its intra-oral site and was swallowed, there was no danger of the F being absorbed into the blood stream.…”

Effect of tamarind ingestion on fluoride excretion in humans

“…Renal clearance of fluoride showed large day-to-day variations depending on renal flow but extra renal clearance representing mainly clearance to bone pool and the fraction of intake remaining in pool bone pool showed remarkable consistency. In a subsequent study, the renal clearance of fluoride has been reported to be always lower with acid urine than with alkaline urine (Ekstrand et al, 1978(Ekstrand et al, , 1980. The extra-renal clearance of fluoride to the bone pool of fluoride was also found to be significantly lower during the production of alkaline urine.…”

Fluoride Pharmacokinetics in Infancy

“…Net fractional renal clearance decreased significantly ( r = Although plasma concentrations of fluoride, renal clcarance of fluoride, and fluoride pharmacokinetics have been extensively studied in human adults (27)(28)(29)(30)(31)(32)(33) and renal clearance of fluoride has been studied in children and adolescents (34). the data reported here arc the first concerning infants.…”

“…the area under the plasma concentration curve in a specified subject was greater when the fluoride dose was greater, but between subjects at the same fluoride intake. there was considerable variability in the area under the plasma concentration curve (27,28).…”