(HealthDay News) – Levothyroxine sodium is increasingly prescribed for borderline thyroid hormone levels, according to a study published online Oct. 7 in JAMA Internal Medicine.

Peter N. Taylor, from Cardiff University in the United Kingdom, and colleagues utilized the United Kingdom Clinical Practice Research Datalink to identify 52,298 individuals who received a prescription for levothyroxine between Jan. 1, 2001, and Oct. 30, 2009. Data were extracted pertaining to thyrotropin levels before and up to five years after levothyroxine therapy initiation.

The researchers found that the median thyrotropin level at the initiation of levothyroxine therapy fell from 8.7 to 7.9mIU/L over the study period. In 2009, the odds ratio for prescribing levothyroxine at thyrotropin levels of ≤10mIU/L, compared with 2001 data, was 1.3. There were higher odds of initiation of levothyroxine therapy with a thyrotropin level ≤10mIU/L among older individuals and individuals with cardiac risk factors. Thyrotropin levels of <0.1mIU/L were seen in 5.8% of individuals five years after levothyroxine initiation. There were increased odds of developing a suppressed thyrotropin level in individuals with depression or fatigue at baseline, whereas individuals with cardiac risk factors did not have increased odds.

“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,” the authors write.

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