Fluoride

The amount of fluoride in the body appears not to be regulated, so that concentrations found in plasma depend on the amount ingested, on the rate of excretion and on bone turnover rate. The first varies with locality and whether fluoride has been added to the drinking water for the purpose of reducing tooth decay. The kidneys are the principal route of excretion and thus plasma concentrations are higher in patients with renal failure. Fluoride in plasma is present as organically bound and ionic forms; it increases proportionally with the concentration in drinking water. The physiological properties of fluoride depend on the ionic activity and its tendency to form highly insoluble calcium fluoride.

Toxicity
Acute exposure to hydrogen fluoride or fluorine by inhalation, or through the skin, leads to severe persistent burning and severe systemic toxicity with dramatic reductions in serum calcium and magnesium concentrations. Acute exposure to excess fluoride causes nausea and diarrhoea. Chronic exposure to sodium fluoride by ingestion leads to osteofluorosis with sclerosis of bones and ligaments. The ability of fluoride to promote the calcification of bone has led to its use in the treatment of patients with severe osteoporosis and crush fractures, who cannot be treated by other means. The dose of fluoride is intended to stimulate osteoblast activity without causing sclerosis. In patients with possible renal impairment, serum fluoride should be monitored regularly during sodium fluoride therapy.

Laboratory indices of fluoride status
Fluoride concentrations can conveniently be measured in either serum or urine.
Prevention of osteofluorosis in workers who are occupationally exposed to fluoride is best conducted by monitoring random urine samples. Pre-shift urine samples collected after 1-2 days away from the workplace reflect the body burden of fluoride, while post-shift sample concentrations are used to monitor the exposure.

References:
Ehrnebo M, Ekstrand J. Occupational fluoride exposure and plasma fluoride levels in man. Int Arch Occup Environ Health 1986; 58: 179-90
Augenstein WL, Spoerke DG, Kulig KW, Hall AH, Hall PK, Riggs BS, El Saadi M, Rumack BH. Fluoride ingestion in children: A review of 87 cases. Pediatrics 1991; 88: 907-12

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