1 in 3 on Levothyroxine Take Meds That Interfere With Thyroid Tests | Nutrition Fit



Approximately a third of older patients treated with thyroid hormones report the concurrent use of medications that can interfere with the accuracy of thyroid function tests, potentially compromising treatment decisions, new research shows.

“We know from previous studies that thyroid hormone use is common in older adults and that there are a multitude of medications that can interfere with thyroid function tests in different ways,” senior author Maria Papaleontiou, MD, told Medscape Medical News.

“However, to our knowledge, the extent of concurrent use of thyroid hormone and interfering medications in older adults, age 65 years and older, has not been previously explored,” added Papaleontiou, of the Division of Metabolism, Endocrinology and Diabetes, Department of Internal Medicine, University of Michigan, Ann Arbor.

The findings were presented as a poster during virtual ENDO 2021, the Endocrine Society’s annual meeting.

Commenting on the study, Thanh Duc Hoang, DO, an endocrinologist with the Walter Reed National Military Medical Center, in Silver Spring, Maryland, said: “It is important for clinicians to be aware of various interactions and interferences of medications affecting the accuracy of thyroid function tests.”

“If patients are not able to discontinue the medications shortly before the bloodwork, the clinicians may consider ordering different thyroid tests or assays that avoid the interferences,” he told Medscape Medical News.

32% of Patients Taking Meds That Could Interfere With Tests

In evaluating data on 538,137 patients treated with thyroid hormones from the Corporate Data Warehouse of the Veterans Health Administration, spanning 2004-2017, first author Rachel Beeson, MD, and colleagues with the University of Michigan found most patients in the study were men (96.5%), White (77.1%), and had two or more comorbidities (62.6%).

Of this total, 170,261 (31.6%) patients treated with thyroid hormones, over a median follow-up of 56 months, were taking at least one drug that could potentially interfere with thyroid function tests

Among the drugs with potential thyroid test interference, about 28% of patients were taking prednisone or prednisolone, 8% were taking amiodarone, and 1.42% were taking phenytoin. Other reported drugs that could potentially interfere included carbamazepine (0.91%), phenobarbital (0.15%), lithium (0.40%), and tamoxifen (0.11%).

Multivariate analysis showed that characteristics associated with those most likely to have concurrent medication use included non-Whites (OR, 1.18 vs Whites), Hispanic ethnicity (OR 1.11 vs non-Hispanic), female sex (OR 1.12 vs males), and presence of comorbidities (eg, Charlson-Deyo comorbidity score ≥ 2, OR,  2.47 vs score of 0).

Meanwhile, older patients age 85 years and over had a lower likelihood of concurrent medications interfering with thyroid tests (OR, 0.47 vs age 65-74 years).

The findings are concerning given the wide use of levothyroxine to treat hypothyroidism, which is the most widely prescribed drug in the United States.

“Our findings not only highlight the complexity of thyroid hormone management in older adults in the context of polypharmacy and multimorbidity, but they also draw attention to vulnerable groups for this practice, which included female patients, non-Whites, patients of Hispanic ethnicity, and patients with comorbidities,” Papaleontiou said.

Nature of Interference Possibilities Varies

Medications or supplements can interfere with thyroid function tests in a variety of ways, she explained. “Some medications could lead to a decrease in the absorption of levothyroxine, others may affect how well the pill dissolves.”

In addition, certain medications can affect the circulation of thyroid hormone in the blood and how it binds with proteins, or they can lead to decreasing thyroid hormone levels due to a variety of interactions.

And in contrast, “What is even more challenging is that some medications or supplements may appear to affect thyroid function based on lab tests when in reality they don’t actually affect thyroid function and may lead to dose adjustments unnecessarily,” Papaleontiou noted.

Recommendations to Counter Interference

Current recommendations to try to counter the effects of polypharmacy on thyroid treatment include advising patients to take thyroid hormones on an empty stomach at least 30-60 minutes prior to eating for optimal absorption.

If the patient is taking medications known to interfere with absorption of thyroid hormones, the recommendation is to space those out by at least 4 hours.

“The big challenge in older adults is that many of them do experience polypharmacy, being at risk for multiple drug-drug interactions,” Papaleontiou said.

“Physicians and patients should be vigilant and communicate closely every time there is initiation of a new medication or supplement to consider whether there may be interference.”

The authors have reported no relevant financial relationships. Hoang has reported being a speaker for Acella Pharmaceuticals.

ENDO 2021. Abstract P51-1. Presented March 20, 2021.

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