Aspects of the absorption of oral L-thyroxine in normal man
Abstract
Using a double isotope method, the optimal conditions for the absorption of an L-thyroxine (L-T4) preparation were examined. In particular, the influence of food intake on L-T4 absorption was examined. As distinct from the unfavorable results hitherto obtained with L-T4 lactase mixtures, a tablet similar to a commercial 100 mug L-T4 lactose preparation showed good absorptionof 70.6% +/- 12.9% SD. In the fasting state, the L-T4 absorption of both preparations was significantly better (p less than 0.001) than with simultaneous food intake: 79.3% +/- 7.2% SD versus 63.9% +/- 10.5% SD. The calculated absorption of a 3-mg L-T4 dose in a lactose preparation used in testing thyroid suppressibility was significantly lower (p less than 0.001) than the absorption of a smaller L-T4 dose, and the absorption in the fasting state was again signifiantly (; less than 0.01) higher compared to that with simultaneous food intake: 52.6% +/- 4.3% SD versus 43.9% +/- 5.4% SD. The possibility of retention in the liver in the case of a large 3-mg L-T4 dose is indicated. The data suggest that with L-thyroxine medication simultaneous food intake should be avoided.
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The absorption of an orally administered dose of LT4 is about 70%-80% under optimum fasting conditions.
“The absorption of an orally administered dose of LT4 is about 70%-80% under optimum fasting conditions (38,119,120).”
From Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement (2014) · cites this paper as [120]
The double isotope study of LT4 absorption with food was limited by participants not serving as their own controls.
“which is limited by the participants not serving as their own controls”
From Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement (2014) · cites this paper as [120]
When LT4 is co-administered with food, absorption is reduced compared with absorption in the fasting state.
“When LT4 is co-administered with food, absorption is reduced compared with absorption in the fasting state.”
From Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement (2014) · cites this paper as [120]
In one study using double isotope methods in healthy volunteers, LT4 absorption with food was 64% compared with 80% in the fasting state (120).
“In one study using double isotope methods in healthy volunteers, which is limited by the participants not serving as their own controls, the documented LT4 absorption with food was determined to be 64% compared with 80% in the fasting state (120).”
From Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement (2014) · cites this paper as [120]
The bioavailability of LT4 is 65-80% in fasting euthyroid subjects and hypothyroid patients.
“The bioavailability of LT4 is 65–80% in fasting euthyroid subjects and hypothyroid patients [ 16 , 17 ].”
From Factors influencing the levothyroxine dose in the hormone replacement therapy of primary hypothyroidism in adults (2022) · cites this paper as [17]
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- Authors
- Wenzel, K. W., & Kirschsieper, H. E.
- Affiliations
- Freie Universität Berlin (DE)
- Corresponding author
- Wenzel, Klaus W.
- Venue
- Metabolism
- Publisher
- Elsevier BV
- Published
- 1977-01
- Volume
- 26
- Issue
- 1
- Pages
- 1-8
- ISSN
- 0026-0495 (ISSN-L)
- OpenAlex
- W1973213396
- Cited by
- 151
- References
- 19
- Citations by year
- 2026: 4 · 2025: 6 · 2024: 5 · 2023: 7 · 2022: 8 · 2021: 9 · 2020: 5 · 2019: 3 · 2018: 7 · 2017: 5 · 2016: 9 · 2015: 7 · 2014: 4 · 2013: 5 · 2012: 6
- FWCI
- 2.44
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Metabolism (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmaceutical Science › Drug Solubulity and Delivery Systems
- Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Pharmacogenetics and Drug Metabolism
- Keywords
- levothyroxine, oral absorption, dietary intake, double isotope method, dose-dependent absorption
- MeSH terms
- Administration, Oral, Adult, Biological Transport, Fasting, Female, Humans, Intestinal Absorption, Kinetics, Male, Middle Aged, Thyroxine
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