Nearly one-third of seniors who take thyroid hormone also take drugs known to interfere with tests of thyroid function, a new study finds.
It's common for older adults to take a thyroid hormone (levothyroxine) to treat low levels of natural thyroid hormone. But tests used to determine the dose and effectiveness of treatment can be affected by other medications, including prednisone, prednisolone, carbamazepine, phenytoin, phenobarbital, amiodarone, lithium, interferon-alpha and tamoxifen.
"Our study highlights the complexity and challenges of managing thyroid hormone replacement in older patients, many of whom are at risk for adverse effects in the context of having multiple chronic conditions and being on multiple other medications," said senior researcher Dr. Maria Papaleontiou, an assistant professor at the Institute of Healthcare Policy and Innovation at the University of Michigan.
For the study, the researchers collected data on more than 538,000 patients age 65 and older who used thyroid hormone and were listed in a U.S. Veterans Health Administration database from 2004 to 2017.
About 32% were taking medications known to interfere with thyroid function tests. Non-white patients, Hispanics, women and those with other medical conditions were most likely to be doing so.
Researchers also found that people 85 and older were less likely to be taking thyroid hormone and interfering medications.
"Thyroid hormone use is common in older adults, and its management is complicated by the fact that many older patients often also use multiple medicines for numerous chronic conditions," Papaleontiou said. "This may increase the risk of drug interactions and the potential for side effects. It is important to be vigilant to ensure safe medication use in our older patients."
One expert not part of the study said doctors often overlook the possibility of drugs interacting with thyroid hormone, which can result in either giving too much of the hormone or too little.
"The fact that certain medications can interfere with the thyroid hormone tests is a very important point to highlight and is often overlooked," said Dr. Minisha Sood, an endocrinologist at Lenox Hill Hospital in New York City.
Too little thyroid hormone can weaken or slow the heart, causing fatigue. It can also cause obesity, joint pain, high blood pressure, swelling in the ankles and high cholesterol. Too much thyroid hormone can cause an irregular heartbeat.
It's important for patients to ask whether certain supplements or medications should be adjusted before they have blood tests to check their thyroid hormone levels, Sood said. Health care providers can use this information to guide patients' medication use.
"For example, in a patient who has stable thyroid levels for years but then develops low thyroid hormone levels without symptoms of being overmedicated, one might rule out concurrent medications, such as prednisone, as the causative factor," Sood said.
The study findings were scheduled to be presented Thursday at an online meeting of the Endocrine Society. Research presented at meetings is typically considered preliminary until published in a peer-reviewed journal.
There's more about the thyroid hormone levothyroxine at the U.S. National Library of Medicine.
SOURCES: Maria Papaleontiou, MD, assistant professor, Institute of Healthcare Policy and Innovation, University of Michigan, Ann Arbor; Minisha Sood, MD, endocrinologist, Lenox Hill Hospital, New York City; Endocrine Society, online meeting presentation, March 18, 2021