February 26, 2016
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Levothyroxine requirement decreases in hypothyroidism after bariatric surgery

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In most people with hypothyroidism, weight loss after bariatric procedures is associated with a reduction of levothyroxine requirements, study data show.

“The reduction of the [levothyroxine] dose observed in the majority of patients was not related to the extent of weight loss nor to reduction of serum leptin, in agreement with the view that [levothyroxine] requirements are independent of the fat mass,” the researchers wrote.

Paula Fierabracci, MD, of the Obesity Center, Endocrinology Unit 1 at the University Hospital of Pisa in Italy, and colleagues evaluated 93 adults (mean age, 48 years) with obesity (mean BMI, 45.9 kg/m2) and hypothyroidism before and 28 months after bariatric surgery to determine levothyroxine requirements before and after weight loss achieved with the surgery. Twenty participants also had data of body composition evaluated by DXA.

Body weight, BMI and serum leptin were all markedly reduced after surgery (P < .001 for all). There was an 11% reduction in mean total dose of levothyroxine (P < .001), but a significant increase (27%) was found for levothyroxine dose per kilogram of body weight (P < .001).

Fifty percent of the study group needed a reduction of the total levothyroxine dose, 37% had unchanged dose and 12 participants needed their dose increased. For participants who required a dosing reduction, the final dose was 1.46 µg/kg; in those who required a stable dose, 1.4 µg/kg; and 1.5 µg/kg in those who required an increase. Autoimmune thyroiditis was present in all participants who needed an increase in their levothyroxine dose with their initial dose being lower (0.84 µg/kg) compared with the other participants (1.17 µg/kg).

“The weight loss that is achieved with modern surgical bariatric procedures is associated with a reduction of [levothyroxine] requirements in about half of the hypothyroid subjects, which appears related to a decrease of the lean body mass. ... During the weight-loss phase that follows bariatric surgery, there is no need for preventive adjustments of the [levothyroxine] dose, but serum thyroid hormones and [thyroid-stimulating hormone] should be periodically monitored, to detect possible variations of [levothyroxine] requirements and to allow proper corrections of the therapy,” the researchers wrote. – by Amber Cox

Disclosure: The researchers report no relevant financial disclosures.