Levothyroxine replacement dosage determination after thyroidectomy.

BACKGROUND: The goal of this study was to identify a simple and effective way of calculating levothyroxine doses for postsurgical hypothyroidism.

METHODS: Levothyroxine dosage was calculated using a weight (μg/kg)-based formula for patients who underwent thyroidectomy for benign disease from 2001 to 2011. Other formulas using age, sex, ideal body weight, body mass index, and body surface area were also evaluated.

RESULTS: Four hundred four patients were included; 85% were women. The mean initial levothyroxine dosage was 1.4 μg/kg, which resulted in thyroid-stimulating hormone normalization in 59%, suppression in 23%, and elevation in 18% of patients. After dose adjustments, the mean therapeutic levothyroxine doses after total thyroidectomy and lobectomy were 1.5 and 1.3 μg/kg, respectively. A regression model incorporating other patient factors did not produce a more reliable dosing regimen.

CONCLUSION: A 1.5- and 1.3-μg/kg dosage calculation based on actual weight is currently the best estimation for levothyroxine replacement therapy after thyroidectomy.