Liquid liothyronine to obtain target TSH in differentiated thyroid cancer patients

Abstract

In the last ten years a liquid formulation of liothyronine (L-T3) became available. To date, no studies on its systematic use have been reported. This study is aimed at assessing the reliability of liquid L-T3 in achieving target TSH in patients with differentiated thyroid cancers (DTC). Twenty-one high risk DTC patients in whom levothyroxine treatment up to 2.0 μg/kg/day did not suppress TSH levels (i.e. >0.1 mIU/L) were selected. Maintaining the same L-T4 dose, they started to assume liquid L-T3 at an initial fixed dose of 3.55 μg (5 drops). Further adjustments of L-T3 dose were tailored according to individual assessment. Initial serum TSH ranged from 0.8 to 12.0 mIU/L, when patients assumed high dose of L-T4 alone. Following the addition of a daily single dose of 3.55 μg L-T3, the target TSH was attained in five patients (23.8%). After increasing L-T3 dose up to a mean of 7.3±3.4 μg/day all patients reached target serum TSH (<0.1 mIU/L). The mean individual L-T3 dose was significantly correlated with the body weight and was 0.11±0.04 μg/kg/day (p=0.013). Mean L-T4:L-T3 ratio was 21:1. No patients showed skewed free-T₃ or free-T₄ values, neither experienced discomfort nor reported adverse events. Liquid L-T3 can be useful to achieve optimal TSH suppression in high risk DTC with not suppressed TSH on L-T4 alone. This formulation allows an individual tailoring of L-T3, minimizing risks of side effects as well as of overtreatment in these clinical conditions.