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Endocrine. 2017 Apr;56(1):138-145. doi: 10.1007/s12020-017-1244-2. Epub 2017 Feb 3.

Undertreated hypothyroidism due to calcium or iron supplementation corrected by oral liquid levothyroxine.

Author information

1
Department of Clinical and Experimental Medicine, University of Messina, Viale Gazzi,, 98125, Messina, Italy.
2
Master Program on Childhood, Adolescent and Women's Endocrine Health, University of Messina, Viale Gazzi,, 98125, Messina, Italy.
3
Interdepartmental Program of Molecular & Clinical Endocrinology, and Women's Endocrine Health, University Hospital, Policlinico Universitario G. Martino, Viale Gazzi,, 98125, Messina, Italy.
4
Department of Clinical and Experimental Medicine, University of Messina, Viale Gazzi,, 98125, Messina, Italy. roberto.vita@yahoo.it.

Abstract

PURPOSE:

The aim of this study was to assess whether oral liquid levothyroxine would correct tablet levothyroxine malabsorption induced by calcium or iron, two sequestrants of levothyroxine.

METHODS:

Nineteen adult hypothyroid patients with tablet levothyroxine malabsorption caused by calcium and/or iron supplements were switched from tablet to liquid levothyroxine at the same dose. Primary outcomes were: (1) significantly lower mean serum thyroid-stimulating hormone with the liquid compared with the tablet formulation, and (2) significantly greater rate of serum thyroid-stimulating hormone less than or equal to 4.12 or 2.5 mU/L.The mean follow-up was 25.2 ± 16.5 weeks.

RESULTS:

TSH was lower with liquid levothyroxine compared with tablet levothyroxine (7.48 ± 5.8 vs. 1.95 ± 1.3 mU/L, P < 0.001), both in the calcium group (8.74 ± 7.2 vs. 2.15 ± 1.4, P < 0.001) and iron group (8.74 ± 7.2 vs. 1.68 ± 0.9, P < 0.001). Thyroid-stimulating hormone levels ≤4.12 mU/L in all patients, calcium group and iron group were more frequent post-switch (95, 87 and 100%) compared to pre-switch (26, 22 and 29%, P < 0.001), and so were thyroid-stimulating hormone levels ≤2.50 mU/L (66, 59 and 76% compared to 5, 9 and 0%, P < 0.001). The pattern held comparing the first liquid levothyroxine thyroid-stimulating hormone levels and the first tablet levothyroxine thyroid-stimulating hormone levels or the corresponding rates of thyroid-stimulating hormone levels below the target.

CONCLUSIONS:

Liquid levothyroxine is resistant to the sequestration by calcium or iron. The high rate of thyroid-stimulating hormone normalization already at the first check (6-8 weeks) should avoid frequent adjustments in levothyroxine doses and assays of thyroid-stimulating hormone, with consequent financial savings.

KEYWORDS:

Hypothyroidism; Levothyroxine replacement therapy; Malabsorption of levothyroxine; Undertreated hypothyroidism

PMID:
28155174
DOI:
10.1007/s12020-017-1244-2
[Indexed for MEDLINE]

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