According to a new study published in in JAMA Internal Medicine, most U.S. prescriptions for the thyroid hormone replacement drug levothyroxine are not appropriate for patients with mild subclinical hypothyroidism.  However, the medicine continues to be prescribed despite “evidence showing no significant benefits for those patients,” according to the report.Subclinical hypothyroidism is an early form of condition.  It’s referred to as “subclinical” because “only the serum level of thyroid-stimulating hormone from the front of the pituitary gland is a little bit above normal.”  These hormones help support heart, brain, and metabolism.“There have been previous reports of increased levothyroxine overuse in the U.S., but this is the first paper to describe the nature of the drivers of the overuse,” explained first author Juan P. Brito, MD, of the Division of Endocrinology, Diabetes, Metabolism & Nutrition, Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota.

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Brito and colleagues analyzed data of adults enrolled in Medicare Advantage who filled levothyroxine prescriptions in the ten-year span between January 2008 and December 2018 and had thyrotropin levels measured within three months prior to the prescription.  The team discovered, “only 8% of those receiving levothyroxine had overt hypothyroidism.”Levothyroxine replaces or provides more thyroid hormone, which is normally produced by the thyroid gland in patients who have low thyroid hormone levels.  Having enough of the hormone is important for normal mental and physical function.Of the “110,842 patients who started levothyroxine during the study period, there were no significant changes in median thyrotropin levels at the time of treatment initiation, with a median level in 2008 of 5.8 mIU/L and a level in 2018 of 5.3 mIU/L (P = .79),” the authors concluded.“These results suggest substantial overuse of levothyroxine during the entire duration of the study, suggesting opportunities to improve care,” the authors wrote.  “The findings underscore the need to improve awareness of the ongoing overuse.  We hope [this study] resonates as a call to action for clinicians to stop treating patients with mild subclinical hypothyroidism.”A study published in the same journal in 2014 noted, “Rates of thyroid hormone prescribing in the United States and the United Kingdom have increased substantially.  If some of the increase is due to lowering the thyrotropin threshold for treatment, this may result in less benefit and greater harm.  Levothyroxine sodium prescriptions in the United States have increased substantially in recent years (from 49.8million in 2006 to 70.5million in 2010).  A similar increase has been observed in England and Wales, with levothyroxine prescriptions rising from 17.1 million (in 2006) to 23.4 million (in 2010).”The authors of this previous study concluded, “Individuals’ baseline characteristics seemed to substantially influence the odds of developing suppressed thyrotropin levels at 5 years after levothyroxine initiation” (i.e., being female and/or experiencing tiredness or depression).  They indicated, “We observed a trend toward levothyroxine treatment of more marginal degrees of hypothyroidism and a substantial risk of developing a suppressed thyrotropin level following therapy.”

Sources:

Levothyroxine Overprescribing Is Common, Consistent Over TimeOveruse of Levothyroxine in Patients With Subclinical Hypothyroidism: Time to “Leve”-Out-ThyroxineFalling Threshold for Treatment of Borderline Elevated Thyrotropin Levels—Balancing Benefits and Risks Evidence From a Large Community-Based StudyWhat Is Subclinical Hypothyroidism?Levothyroxine Solution