Impaired Pharmacokinetics of Levothyroxine in Severely Obese Volunteers
Abstract
BACKGROUND: Suppressive or replacement doses of levothyroxine (LT4) are affected by the rate and extent of the active ingredient absorbed, as well as by the lean body mass. Obesity has reached epidemic proportions worldwide and is related with many comorbidities. The aim of this study was to determine the pharmacokinetic parameters of LT4 in severely obese individuals and compared them with similar data in lean control subjects. METHODS: We studied 62 euthyroid subjects who had negative tests for anti-thyroid peroxidise antibodies (Ab-TPO). Thirty eight of these subjects were severely obese but otherwise healthy (severe obese subjects [SOS] group). Twenty-four were healthy control subjects (control group), with a body mass index of 23.3 ± 1.7 kg/m(2). Subjects received 600 μg oral sodium LT4 after an overnight fast. Serum triiodothyronine (T3), T4, and thyroid-stimulating hormone were measured at baseline. Serum T4 and T3 was measured 0.5, 1, 1.5, 2, 2.5, 3, and 4 hours after LT4 administration. RESULTS: Baseline serum T4 and thyroid-stimulating hormone concentrations were higher in the SOS group than in the control group; serum T3 was similar in the two groups. The corrected area under the curve and the maximum T4 concentration after LT4 administration were lower, whereas the time to maximum concentration from the baseline was higher in SOS than in the control group. The estimated plasma volume was higher in the SOS than in the control group. Mean serum T3 levels increased gradually during the four hours after LT4 administration in the control group. In contrast, they decreased gradually in the SOS group. CONCLUSIONS: Severely obese individuals may need higher LT4 suppressive or replacement doses than normal-weight individuals due, among other factors, to impaired LT4 pharmacokinetic parameters. The latter could be attributed to their higher plasma volume and/or to delayed gastrointestinal LT4 absorption. T4 conversion to T3 might be defective in severe obesity.
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Advancing age and extreme obesity (BMI > 40 kg/m2) are associated with decreased LT4 absorption.
“Examples of factors that are also associated with decreased absorption are advancing age (35) and extreme obesity (body mass index [BMI] > 40kg/m 2 ) (163).”
From Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement (2014) · cites this paper as [163]
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A rare case of acrohygiantism caused by Carney’s complex: diagnostic and treatment challenges
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- Authors
- Michalaki, M. A., Gkotsina, M. I., Mamali, I., Markantes, G. K., Faltaka, A., Kalfarentzos, F., Vagenakis, A. G., & Markou, K. B.
- Affiliations
- University of Patras (GR)
- Division of Endocrinology, Department of Internal Medicine; University Hospital of Patras, Patras, Greece.
- General University Hospital of Patras (GR)
- Corresponding author
- Markou, Kostas B.
- Venue
- Thyroid
- Publisher
- SAGE Publications
- Published
- 2011-05
- Volume
- 21
- Issue
- 5
- Pages
- 477-481
- ISSN
- 1050-7256 (ISSN-L)
- 1557-9077
- OpenAlex
- W2029483174
- Cited by
- 34
- References
- 24
- Citations by year
- 2026: 1 · 2025: 4 · 2024: 2 · 2023: 2 · 2022: 1 · 2021: 4 · 2020: 3 · 2019: 5 · 2018: 2 · 2017: 1 · 2016: 3 · 2015: 1 · 2014: 3 · 2012: 1
- FWCI
- 1.04
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Thyroid (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Medicine › Surgery › Thyroid and Parathyroid Surgery
- Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Pharmacogenetics and Drug Metabolism
- Keywords
- levothyroxine, pharmacokinetics, morbid obesity, thyroid hormone replacement, thyroid-stimulating hormone, triiodothyronine, plasma volume, gastrointestinal absorption, T4 to T3 conversion, lean body mass, dose adjustment
- MeSH terms
- Adult, Autoantibodies, Body Weight, Female, Humans, Male, Obesity, Thyroid Hormones, Thyrotropin, Thyroxine, Triiodothyronine, Cohort Studies, Body Mass Index, Case-Control Studies, Area Under Curve
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