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Fluoride-liberating chemicals are found in some automobile wheel cleaners, rust removers, glass-etching solutions, pesticides, agents used in aluminum production, and vitamins and dietary supplements, and also in products used to prevent dental caries. Most toothpaste contains up to 5 mg of fluoride per teaspoon, and tea can contain 0.3–5.1 mg of fluoride per liter. Fluoride is commonly added to community drinking water and is a natural ground water contaminant in some parts of the world. It is also found in hydrofluoric acid (See Hydrogen Fluoride and Hydrofluoric Acid), which is used for etching glass and silicon chip products. Soluble fluoride salts are rapidly absorbed and are more acutely toxic (Table II–25).

Table II-25 Fluoride-Containing Compounds

  1. Mechanism of toxicity

    1. In addition to its direct cytotoxic and metabolic effects, fluoride binds avidly to calcium and magnesium, causing hypocalcemia and hypomagnesemia. Fluoride toxicity disrupts many intracellular mechanisms, including glycolysis, G-protein–mediated signaling, oxidative phosphorylation, adenosine triphosphate (ATP) production, function of Na+/K+-ATPase, and potassium channels.

    2. Pharmacokinetics. Fluoride is a weak acid (pKa = 3.4) that is passively absorbed from the stomach and small intestine. In an acidic environment, more fluoride is present as hydrogen fluoride (HF), which is absorbed more rapidly. Fasting peak absorption occurs in 30–60 minutes. The volume of distribution is 0.5–0.7 L/kg. Fluoride is not protein-bound but binds readily to magnesium and calcium in blood and tissues and is deposited in bone. The elimination half-life is 2.4–4.3 hours and is prolonged in patients with renal failure.

  2. Toxic dose. Vomiting and abdominal pain are common with ingestions of elemental fluoride of 3–5 mg/kg (see Table II–25); hypocalcemia and muscular symptoms appear with ingestions of 5–10 mg/kg. Death has been reported in a 3-year-old child after ingestion of 16 mg/kg and in adults with doses in excess of 32 mg/kg.

  3. Clinical presentation

    1. Acute poisoning. Nausea and vomiting frequently occur within 1 hour of ingestion. Symptoms of serious fluoride intoxication include skeletal muscle weakness, tetanic contractions, respiratory muscle weakness, and respiratory arrest. Hypocalcemia, hypomagnesemia, hyperkalemia, and increased QT interval can occur. Death is due to intractable cardiac dysrhythmias and usually occurs within 6–12 hours.

    2. Chronic effects. The recommended daily limit for children is 2 mg and for adults is 4 mg. Minor overexposure in children younger than age 10 can cause tooth discoloration. Chronic overexposure (>20 mg/d for >10 years) can cause skeletal fluorosis (osteosclerosis), ligament calcification, and increased bone density.

  4. Diagnosis usually is based on a history of ingestion. Symptoms of Gl distress, muscle weakness, hypocalcemia, and hyperkalemia suggest acute fluoride intoxication.

    1. Specific levels. The normal serum fluoride concentration is less than 20 mcg/L (ng/mL) but varies considerably with diet and water source. ...

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