Hi Everyone,
For some reason the topic of fluoride came up in class discussion
today in my basic Pharmacology class, as to the value of fluoride and
what happens if you take too much fluoride? Keep in mind most city
water systems include fluoride in their drinking water, with
toothpaste touting having added fluoride and marketing of fluoride
supplementation including mouth rinses, maybe overdoing fluoride is
more of a possibility than we want to believe.
Joe Medina, CPhT
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Fluoride
TRADE NAMES
Neutracare (Oral B Laboratories), Fluorigard (Colgate Oral
Pharmaceuticals), Neutragard Fluoride Rinse (Pascal Co.), Phos-Flur
(Colgate Oral Pharmaceuticals)
DESCRIPTION
In the 1930s, it was discovered that high fluoride intake was
responsible for a dental condition which is characterized by mottled
enamel and which is known as dental fluorosis. Observational studies
at the time led to the conclusion that those who lived in areas with a
high incidence of dental fluorosis also had a lower incidence of
caries than those who lived in areas where the fluoride intake was low.
In 1945, water fluoridation began in Grand Rapids, Michigan as a
public health measure to reduce the incidence of caries. Presently,
approximately 60% of community water supplies in the United States
contain fluoride from 0.7 to 1.2 parts per million or 0.7 to 1.2
milligrams per liter.
Fluoride is the anionic form of fluorine. Fluorine is a halogen gas
with atomic number 9 and an atomic weight of 19 daltons. Its symbol is
F. Fluorine is the most electronegative element in the periodic table
and, in size, it is very similar to the first element, hydrogen.
Even though fluoride has a beneficial role in the protection against
caries, there is no evidence that fluoride is an essential nutrient
for humans. The only evidence that it may be essential for higher
animals is a recent report that fluoride deficiency in goats decreased
life expectancy and caused pathological findings in the kidneys and
endocrine organs. Fluoride, in addition to being found in municipal
drinking water, is found in many foods. Particularly rich sources of
fluoride are teas and marine fish.
ACTIONS AND PHARMACOLOGY
Actions
Fluoride may have cariostatic and anti-osteoporotic activities.
MECHANISM OF ACTION
The mechanism of the cariostatic activity of fluoride is not
completely understood. It is thought that fluoride interacts with
hydroxyapatite to form the less acid soluble fluorhydroxyapatite.
Fluorhydroxyapatite is believed to be more resistant to dissolution by
the acids produced by bacteria found in plaque. Fluoride may also
promote the remineralization of enamel in early caries. Finally
fluoride may reduce oral concentrations of cariogenic bacteria or
reduce the metabolism of bacteria in plaque.
The mechanism of the possible anti-osteoporotic activity of fluoride
is also incompletely understood. Fluoride is thought to have
osteoblastic activity and, in partnership with calcium, stimulates the
production of new bone. Insufficient intake of calcium at the time
that fluoride is administered could lead to osteoid formation and
osteomalacia. Fluoride is incorporated in the crystalline structure of
bone as fluoroapatite. Fluoride may also slow the resorptive phase of
the remodeling process and promote calcification.
PHARMACOKINETICS
Approximately 75% to 90% of ingested fluoride is absorbed from the
gastrointestinal tract. About 50% of ingested fluoride is absorbed
after 30 minutes. Absorption appears to occur by passive diffusion. A
large fraction of ingested fluoride is absorbed from the stomach.
Fluoride absorbed from the stomach appears to be absorbed as
hydrofluoric acid. Fluoride absorbed from the small intestine is
absorbed as fluoride. Slow-release sodium fluoride preparations are
principally absorbed from the small intestine as fluoride. Concomitant
intake of fluoride with antacids of the aluminum hydroxide type or
high doses of calcium can cause decreased absorption of fluoride.
Fluoride may form insoluble compounds with aluminum hydroxide and calcium.
For healthy, young, or middle aged adults, approximately 50% of
absorbed fluoride is deposited in calcified tissues and 50% is
excreted in the urine. For young children, up to 80% is deposited in
bone and developing teeth. From 5% to 10% of ingested fluoride is
excreted in the feces.
INDICATIONS AND USAGE
Fluoride, in appropriate doses, protects against dental caries. Its
use in the treatment of osteoporosis remains controversial and
experimental. A trend toward increased fluoride exposure has
heightened concerns related to enamel and skeletal fluorosis, the
incidences of which, however, still remain low.
RESEARCH SUMMARY
Sodium fluoride is approved by the Food and Drug Administration (FDA)
for the prevention of dental caries. Fluoride is often added to public
water supplies to achieve concentrations of 0.7 to 1.2 ppm. Higher
concentrations (in the maximum 1.2 ppm range) are used in colder
climates and lower concentrations in warmer climates where more water
is typically consumed.
Epidemiological data show that low fluoride consumption is
significantly associated with a higher incidence of dental caries.
Experimental and clinical studies provide further substantial support
for these epidemiologic findings. Numerous studies have shown that
benefits are greatest when teeth get adequate pre-eruptive, as well as
posteruptive, fluoride exposure.
Concerns have grown in recent years, however, that some children may
be over-exposed to fluoride. Despite some reduction in exposure levels
recommended by the American Academy of Pediatrics, incidence of dental
fluorosis, while small, has continued to increase, a finding that some
attribute to increased opportunities for fluoride exposure, not only
from water but also from oral supplements, toothpastes, rinses, gels
and some processed foods and beverages. Further modifications in
recommended exposure levels are under consideration.
Because it is an effective osteoblast stimulator, fluoride has been
investigated as a treatment for osteoporosis. It has shown some
usefulness in this regard, particularly when given in the earliest
stages of osteoporosis and particularly in patients with intact
trabecular bone. Its effectiveness appears to be enhanced when
combined in low doses with vitamin D and calcium.
Fluoride's efficacy in osteoporosis, however, is far from established.
Where benefit has been demonstrated it has often been modest. Some
studies have shown that it has no benefit. In one study, fluoride plus
calcium decreased vertebral fracture rates, compared with calcium
alone, in postmenopausal women with moderate osteoporosis. The dose of
fluoride was 20 milligrams per day. In another recent study, a
fluoride/calcium/vitamin D regimen was no more effective than a
calcium/vitamin D regimen in preventing new vertebral fractures in
women with postmenopausal osteoporosis.
Some have reported that fluoride-stimulated bone has abnormal texture
and is less mineralized and durable than healthy bone. In some
studies, despite increased bone mineral density, an increased
incidence of fracture has been reported. Additionally, some have
reported upper gastrointestinal discomfort and, of greater concern,
lower extremity pain syndrome said to be caused by stress fractures.
Thus, the benefits of fluoride in the treatment of osteoporosis remain
in doubt. And its use in this context remains experimental.
There have been some cases of skeletal fluorosis associated with
fluoride supplementation, particularly in those with various forms of
renal failure. Two cases of bilateral hip fracture were reported
involving women (aged 69 and 78) receiving 40 to 60 milligrams of
fluoride daily for 11 to 21 months, in combination with calcium and
vitamin D. Both women had moderate renal failure. Histological
examination of a bone specimen from the 69-year-old patient revealed
