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April 30, 2011

A new study shows an increased risk of bone fractures for elderly people taking levothyroxine thyroid medications.

Levothyroxine is a synthetic form of the hormone thyroxine produced by the thyroid gland. The U.S. Food and Drug Administration (FDA) has approved levothyroxine for the treatment of conditions characterized by diminished or absent thyroid function, such as cretinism, myxedema, nontoxic goiter or hypothyroidism. Physicians may prescribe this drug for “off-label” uses not approved by the FDA.

Levothyroxine is one of the most frequently prescribed drugs in the United States with more than 13 million Americans using levothyroxine drugs daily and most taking it chronically for many years.

Researchers from Canada’s University of Toronto, Institute for Clinical Evaluative Sciences and the Women’s College Research Institute studied 213,511 people aged 70 and older prescribed levothyroxine between April 2001 and March 2007. They identified 22,236 levothyroxine users (10.4%) who suffered a fracture of the wrist or forearm, upper arm or shoulder, spine, pelvis, leg or ankle during therapy or within six months of stopping therapy with the drug.

The study entitled “Levothyroxine dose and risk of fractures in older adults: nested case-control study” appears in the April 28, 2011 issue of BMJ – British Medical Journal.

They also found that the risk of bone fractures increases as levothyroxine dosage increases. Because most people begin treatment of hypothyroidism between early adulthood and middle age, they can be on levothyroxine therapy for decades and evidence shows that people generally remain on the same dosage throughout their life. However, people need less of this hormone replacement as they age and may be taking a dose much higher than needed, creating a condition called iatrogenic or drug-induced hyperthyroidism.

Women may be especially at risk, reports Med PageToday.

Physicians and drug manufacturers should adequately notify people taking levothyroxine of the increased risk of fractures. Physicians should be re-evaluating their patient’s levothyroxine dosage as they age.

“Our findings provide evidence that levothyroxine treatment may increase the risk of fragility fractures in older people even at conventional dosages, suggesting that closer monitoring and modification of treatment targets may be warranted in this vulnerable population,” study researchers wrote.

Brand names of levothyroxine drugs include Eltroxin, Estre, Euthyrox, Levo-T, Levotabs, Levothroid, Levoxyl, Novothyrox, Synthroid, Thyrox, Unithroid and Thyrolar.

“It has long been known that high or excessive doses of levothyroxine usage predispose [people] to increases in osteoporosis and the risk of fracture,” Dr. Irwin Klein, of North Shore-LIJ Health System in Manhasset, N.Y. told HealthDay News “This study further confirms this finding in an elderly population of women who are inherently at risk for this occurrence.”

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