Endocrine Abstracts

Background: In a previous publication we identified the major predictive factors of levothyroxine (LT₄) requirement and proposed an efficient nomogram to calculate LT₄ substitutive starting dose after total thyroidectomy for benign disease. The aim of this study was to assess whether the LT₄ requirement differs between the tablet and the soft gel capsules formulations.

Methods: One hundred and three consecutive patients submitted to total thyroidectomy for benign disease and were receiving substitutive therapy with LT₄ were enrolled. All patients received the LT₄ tablet formulation. The specific substitutive starting dose was calculated using the previously described nomogram and was aimed at achieving normal TSH levels (0.4–2.5 mU/L). Exclusion criteria were: malignancy at histological examination, symptoms or signs of malabsorption, assumption of drugs or habits interfering with LT₄ absorption, impaired renal function, pregnancy, poor compliance with drug administration. TSH, FT₄, and FT₃ were assessed three months after the switch from tablet to soft gel capsule formulation at the same dose of LT_4. Mean and standard deviation (SD) were used for quantitative variables. The paired t-test was applied in order to compare the thyroid function tests with different formulations of LT₄.

Results: Serum TSH was significantly lower during treatment with soft gel capsules [1.3 mU/L (SD 0.9) and 1.8 mU/L (SD 1.2) respectively, P=0.02]. There were no statistically significant differences for FT₃ and FT₄.

Conclusions: Levothyroxine substitutive dose is not significantly different between soft gel capsules and tablets in patients without malabsorption but TSH is significantly lower with the first one. This datum must be considered in clinical practice, particularly for patients with TSH at limits of the therapeutic range or if a strict therapeutic goal is needed.