Ann Arbor, MI—Testing older patients for thyroid function is often complicated by other medications they have been prescribed.

That’s according to a new study finding that nearly one-third of adults aged 65 years and older who take thyroid hormone also take medications that are known to interfere with thyroid-function tests. Results were presented virtually at ENDO 2021, the Endocrine Society’s annual meeting.

“Our findings highlight the complexity of managing thyroid hormone replacement in older adults, many of whom take medications for other medical conditions,” explained first author Rachel Beeson, MD, of the University of Michigan in Ann Arbor. “Until now, the prevalence of concurrent use of thyroid hormone and interfering medications in older adults, and patient characteristics associated with this practice, has been unknown.”

The problem is that use of thyroid hormone is extremely common in older adults, according to the authors. About 20 million Americans—many of them older—are estimated to have overt or subclinical hypothyroidism and may require thyroid hormone replacement with levothyroxine preparations. In those patients, thyroid-function tests are used to determine the dose and effectiveness of treatment, but results can be skewed by a variety of medications, the study notes.

Researchers analyzed data from 538,137 adults aged 65 years and older who used thyroid hormone, zeroing in on those who concurrently took thyroid hormone and medications that commonly interfere with thyroid-function tests. Those drugs include:
• Prednisone
• Prednisolone
• Carbamazepine
• Phenytoin
• Phenobarbital
• Amiodarone
• Lithium
• Interferon-alpha
• Tamoxifen

Results indicate that, overall, 31.6% of the patients were taking medications that have been shown to interfere with thyroid-function tests.

“When we examined patient characteristics associated with concurrent use of thyroid hormone and at least one interfering medication, this was more likely to be seen in patients who were female, non-white and of Hispanic ethnicity,” Dr. Beeson said.

Researchers also determined that patients who had other chronic medical conditions were more likely to concurrently use thyroid hormone and medications that interfere with thyroid tests.

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