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Women with obesity, total thyroidectomy require higher doses of levothyroxine

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NASHVILLE, Tenn. — A higher levothyroxine dose is required among women with obesity following total thyroidectomy, according to recent study findings.

This is notable as “recommendations for levothyroxine replacement in patients with hypothyroidism are based on the evidence from studies in non-obese subjects,” the researchers wrote.

Kathleen Glymph, DO, an endocrinology fellow at the University of Tennessee in Memphis, and colleagues evaluated 30 women with hypothyroidism between November 2010 and October 2014 who underwent total thyroidectomy for non-toxic goiter or early-stage thyroid cancer and who achieved a euthyroid state on levothyroxine therapy post surgery. The primary outcome was to determine the levothyroxine regimen required for euthyroidism in patients with hypothyroidism with obesity (n = 16) or without obesity (n = 14).  Researchers defined obesity as a BMI of more than 30 kg/m².

Kathleen Glymph

Participants with obesity required a higher levothyroxine dose compared with those without obesity (P = .0002). However, per total body weight, no difference was found for levothyroxine levels (P = .21). Participants with obesity had a higher levothyroxine per ideal body weight compared with participants without obesity (P = .006) and the difference was maintained following adjustment for age and race (P < .05).

There was a marked variability in thyroid replacement dosage among participants with obesity. A subgroup analysis was done comparing participants with obesity who achieved euthyroidism on levothyroxine 150 mcg or less and more than 150 mcg daily. Age, weight, and BMI were not different when comparing participants with obesity assigned to less 150 mcg of levothyroxine compared with more than 150 mcg; however, the group assigned more than 150 mcg were more likely to have a higher levothyroxine dose per total body weight (P = .06) and ideal body weight (P = .002) compared with those assigned to less than 150 mcg.

“Among obese women, there was a significant heterogeneity in final [levothyroxine] dosage,” the researchers wrote. “To prevent iatrogenic hyperthyroidism, we recommend using the [ideal body weight] as opposed to the [total body weight] as a more accurate initial approach for therapy of hypothyroidism in a majority of obese females.” – by Amber Cox

Reference:

Glymph K, et al. Abstract #1019. Presented at: AACE 24th Annual Scientific & Clinical Congress; May 13-17, 2015; Nashville, Tenn.

Disclosure: The researchers report no relevant financial disclosures.