Endocrine Abstracts

Introduction: Oral levothyroxine (L-T₄) is the standard treatment for hypothyroidism and serum TSH represents the best marker for assessing the proper L-T₄ dose. The absorption and bioequivalence of different commercial L-T₄ preparations might be variable. The aim of this study is to compare the efficacy of L-T₄ using alternating doses vs fixed ones.

Methods: Fifty-eight patients with primary hypothyroidism receiving L-T₄ therapy. The inclusion criteria were as follows: i) age range between 23 and 75 years and ii) patients with subclinical hypothyroidism (TSH level between 2.5 and4.5 mU), treated with L-T₄ oral solution at alternating dosages on consecutively days (75 μg/100 μg, group O) or soft capsules (88 μg/day daily, group T), for at least 6 months. The exclusion criteria were as follows: i) pregnancy or lactation; ii) patients with chronic diseases, such as cardiac (coronary disease or arrhythmias), pulmonary, gastrointestinal (malabsorption disorders), and renal disorders or malignancy; and iii) medications that could interfere with L-T₄ absorption.

Results: According to ANOVA for repeated measure with treatment (T vs O group) as between-subjects factor and time (baseline, 45, 90, and 180 days) as within-subjects factor, a significant interaction treatment×time was found (F=3.673, Greenhouse-Geisser df=1.9, 184.6, P=0.028), indicating two different trends of TSH in T and O groups. Contrast analysis (each time vs baseline) showed a stronger TSH decrease after soft capsules at 180 days (O group 2.17±0.55 and T group 1.67±0.59).

Discussion: Our preliminary observation seems to show a possible greater efficacy of L-T₄ at fixed dosage vs alternating and consecutive dosage, as suggested by significant greater decrease of TSH levels in group T. This finding could be related to an improving of adherence to L-T₄ therapy at fixed dosage. Treatment at alternating dosage on consecutive days may not always be accurate. However, prolongation of follow-up is needed to confirm our data.