Lactose intolerance revealed by severe resistance to treatment with levothyroxine
Abstract
The most common cause of apparent ineffectiveness or resistance to treatment with oral levothyroxine (LT(4)) is the result of noncompliance, known as pseudomalabsorption. However, an abnormality in the bioavailability of LT(4) should also be considered in patients requiring large doses of LT(4) to achieve euthyroidism. The incidence of lactose intolerance in Caucasian adult patients is 7%-20%, but the association with resistance to treatment with oral LT(4) is unusual. We report a 55-year-old woman in whom treatment LT(4) for hypothyroidism was found related to a previously undiagnosed oligo-symptomatic lactose intolerance, an unusual association. Although rare, intolerance to lactose should be considered in the differential diagnosis of gastrointestinal diseases that can cause malabsorption of LT(4). The possibility of correcting this disorder with simple dietary measures justifies its consideration.
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There are case reports of increased LT4 requirements in individuals with celiac disease, lactose intolerance, and intestinal giardiasis, with reduction in LT4 requirement after institution of gluten-free or lactose-restricted diet and treatment of infection.
“There are also case reports of increased LT4 requirements in individuals with celiac disease (158,159), lactose intolerance (160), and intestinal giardiasis (161) with reduction in the LT4 requirement occurring after institution of a gluten-free or lactose-restricted diet and treatment of the infection, respectively.”
From Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement (2014) · cites this paper as [160]
Lactose intolerance and celiac disease are among the most frequent intestinal diseases responsible for malabsorption and may both impair intestinal absorption of drugs and nutrients via hydrolysis and complexation.
“In addition to surgery, lactose intolerance and celiac disease are among the most frequent intestinal diseases responsible for malabsorption. They may both impair intestinal absorption of drugs and nutrients via hydrolysis and complexation (25, 26, 55).”
From Levothyroxine: conventional and novel drug delivery formulations. (2023) · cites this paper as [55]
Unusual administration routes, including intravenous (IV) injection and IM injection, can also decrease unsuppressed TSH levels in patients with digestive tract disorders.
“Unusual administration routes, including intravenous (IV) injection and IM injection, can also decrease unsuppressed TSH levels in patients with digestive tract disorders (55, 58, 68, 69).”
From Levothyroxine: conventional and novel drug delivery formulations. (2023) · cites this paper as [55]
To reach an equivalent TSH level, LT4 dose must be higher if the patient's intestinal tract is affected by ulcerative colitis, coeliac disease, lactose intolerance, gastritis (especially H. pylori-related and autoimmune gastritis), and Giardia lamblia infection.
“To reach an equivalent TSH level, the LT4 dose must be higher if the patient’s intestinal tract is affected by ulcerative colitis [ 49 ], coeliac disease [ 50 ], lactose intolerance [ 51 ], and gastritis (especially Helicobacter pylori –related gastritis and autoimmune gastritis) [ 43 , 52 – 54 ], and infections with Giardia lamblia (giardiasis) [ 55 ].”
From Factors influencing the levothyroxine dose in the hormone replacement therapy of primary hypothyroidism in adults (2022) · cites this paper as [51]
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References 11 · Cited by 54
- Authors
- Muñoz-Torres, M., Varsavsky, M., & Alonso, G.
- Affiliations
- Department of Endocrinology, Hospital Universitario San Cecilio de Granada, Granada, Spain.
- Complejo Hospitalario Universitario de Granada (ES)
- ORCID
- Varsavsky, Mariela
- Venue
- Thyroid
- Publisher
- SAGE Publications
- Published
- 2006-11
- Volume
- 16
- Issue
- 11
- Pages
- 1171-1173
- ISSN
- 1050-7256 (ISSN-L)
- 1557-9077
- OpenAlex
- W2066105604
- Cited by
- 54
- References
- 11
- Citations by year
- 2026: 2 · 2025: 1 · 2024: 1 · 2023: 2 · 2022: 4 · 2021: 3 · 2020: 4 · 2018: 2 · 2017: 4 · 2016: 4 · 2015: 2 · 2014: 7 · 2013: 4 · 2012: 2
- FWCI
- 1.33
- 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
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Digestive system and related health
- Health Sciences › Medicine › Gastroenterology › Celiac Disease Research and Management
- Keywords
- lactose intolerance, levothyroxine, treatment resistance, hypothyroidism, drug bioavailability, malabsorption
- MeSH terms
- Drug Resistance, Female, Humans, Hypothyroidism, Intestinal Absorption, Lactose Intolerance, Middle Aged, Thyroxine
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