Level 1: Likely reliable evidence

A randomized crossover trial evaluated the efficacy of different l-thyroxine dosing strategies and different target thyroid-stimulating hormone (TSH) ranges in patients with treated hypothyroidism.

Enrollment criteria were treatment for at least six months, stable l-thyroxine dosing 100-200 µg/day for at least two months, and TSH level 0.1-4.8 mU/L (J Clin Endocrinol Metab. 2006;91:2624-2630). Fifty-six patients were randomized to each of three dosing strategies for eight weeks at a time: low-dose strategy (target TSH 2-4.8 mU/L), middle-dose strategy (25 µg more than low dose, target TSH 0.3-1.99 mU/L), or high-dose strategy (25 µg more than middle dose, target TSH <0.3 mU/L). All doses were adjusted using l-thyroxine 50-µg, 25-µg, or placebo tablets to maintain blinding. There was no washout period between treatments. The baseline mean l-thyroxine dose was 120 µg/day or 1.7 µg/kg/day.

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Fifty patients completed all three treatment arms. Comparing low- vs. middle- vs. high-dose strategies, the mean l-thyroxine doses were 103.2 vs. 127.2 vs. 151.7 µg/day, and mean TSH levels were 2.8 vs. 1 vs. 0.3 mU/L. Patient preferences were 32% vs. 26% vs. 20%; 22% had no preference for a specific dosing strategy (not statistically significant). There were no significant differences in general well-being or any of numerous specific quality-of-life measures; confidence intervals excluded clinically relevant differences.