The study raises new concerns that many elderly people are likely being treated with doses of the drug that are too high for them and that excessive dosing may increase fracture risk in an already high-risk population.
Geriatrician and researcher Paula A. Rochon, MD, MPH, of Toronto’s Women’s College Research Institute, says thyroid hormone levels naturally decline with age, but dosages of hormone-replacement therapy often do not reflect this.
As a result, treated patients may end up with an excess of thyroid hormone, or hyperthyroidism, which has been linked to bone weakening.
“People with thyroid disease often present in middle age and they are treated for the rest of their lives,” she tells WebMD. “As patients age their dose requirements may change.”
Fracture Risk Dose Related
In an effort to better understand the impact of treatment with levothyroxine on fracture risk, Rochon and colleagues analyzed data on more than 200,000 mostly female patients aged 70 and older who were prescribed the drug between April 2002 and March 2007.
Hospital records were used to identify patients who had suffered fractures, and each case was matched with five other patients who had not suffered fractures.
About 10% of the patients had at least one fracture during the follow-up period, which lasted until March of 2008.
Patients who were taking the drug or had taken it recently were found to have a significantly higher fracture risk than people who had taken it and stopped in the more distant past.
Among current levothyroxine users, people who took the highest doses had a 3.5-fold higher risk for fractures of any kind than people who took the lowest doses, Rochon noted.
Even after considering the impact of other risk factors for fracture, treatment with levothyroxine appeared to increase hip fracture risk among both men and women, and the greatest risk was seen in those who took the highest doses of the drug.
Time to Revisit Dosing for Elderly?
Rochon says older patients on thyroid hormone replacement need to be monitored carefully and their dosage may need to be adjusted over time.
Graham Leese, MD, who did not participate in the study, tells WebMD that the risk to individual patients taking levothyroxine is small. But he adds that because so many people are on the drug, the risk must be taken seriously.
Leese is a professor of endocrinology and diabetes at Ninewells Hospital and Medical School in Dundee, U.K.
In an editorial published with the study, Leese wrote that it might be time to revisit levothyroxine dosing recommendations for older patients, especially those at the highest risk for fractures.
The study and editorial appear today in the journal BMJ Online First.