CLINICAL THYROIDOLOGY FOR PATIENTS
A publication of the American Thyroid Association

Summaries for Patients from Clinical Thyroidology by Ernest Mazzaferri, MD MACP
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THYROID HORMONE THERAPY

Abbreviations & Definitions

Levothyroxine (L-T4) is the usual oral form of thyroid hormone that is administered to patients for the treatment of hypothyroidism (thyroid failure) or for the treatment of thyroid cancer when the drug is administered to suppress serum thyrotropin (TSH, thyroid-stimulating hormone) levels. It should be taken on an empty stomach, usually in the morning about an hour after breakfast, although it may be taken before sleep if food has not been ingested for the past hour.

Many things interfere with L-T4 therapy, including compliance (taking the drug as directed), reduced absorption from gastrointestinal disorders such as stomach or duodenal ulcers, malabsorption, liver disease, medications such as iron supplements, antacids, resins, lovastatin (a cholesterol lowering drug), sucralfate (an antacid), calcium carbonate, soybeans, coffee, high-fiber diet, and many other things, such as impaired stomach acid secretion.

Parietal Cells These cells line the stomach wall and produce gastric acid that seems necessary for L-T4 absorption. Patients may develop anti-parietal cell PCA anti-parietal cell antibodies

Autoimmune Thyroid Disease (Hashimoto’s thyroiditis) is a form of thyroiditis that is a frequent cause of hypothyroidism.

Internet information: the link below provides a good source of patient information on this subject: http://www.uptodateonline.com/patients/index.html

What is the study about? Autoimmune atrophic gastritis may affect the intestinal absorption of levothyroxine.

The full article title: “L-thyroxine requirement in patients with autoimmune hypothyroidism and parietal cell antibodies” It is in the February 2008 issue of the Journal of Clinical Endocrinology & Metabolism (Volume 93, Issue 2, pages 465-69. The authors are S Checchi, A Montanaro, L Pasqui,C Ciuoli,V De, Palo, MC Chiappetta, and F Pacini, The abstract can be obtained from:

http://www.ncbi.nlm.nih.gov/pubmed/
18042648?dopt=Citation

What is known about the problem being studied? Based on the frequent association of parietal-cell antibodies (PCAs) with atrophic gastritis and autoimmune thyroid disease, the authors of this study hypothesized that PCA-positive patients may require higher than usual doses of L-T4 and that this may be another cause for increased daily L-T4 requirements

What was the aim of the study? The study was designed to find a relationship between the daily dose of L-T4 and the presence of autoimmune gastritis.

Who was studied? The study subjects were 391 patients taking L-T4 for mild autoimmune hypothyroidism. None had stomach disorders or were taking drugs known to affect L-T4 intestinal absorption. In addition 60 patients who had undergone thyroid surgery for Graves’ disease or multinodular goiter were studied to compare their results the study group results.

How was the study done? Nearly 50% of the patients agreed to undergo stomach biopsy to be examined for atrophic gastritis. Blood was tested for PCA and serum TSH (thyroid stimulating hormone) levels to provide a measurement of the adequacy of L-T4 replacement.

What were the results of the study? The daily L-T4 requirements increased by 17% when parietal cell antibodies were present and 26% when gastric atrophy was present, and increased by 55% when gastric atrophy went from mild to severe.

How does this compare with other studies? Most but not all studies find that reduced gastric acid secretion impairs L-T4 absorption, perhaps because it is not always associated with severe gastric parietal cell atrophy.

What are the Limitations of this study? There are no serious limitations to this study.

What are the implications of this study? The observations in this study suggest that serum parietal-cell antibody levels might be measured when the response to thyroxine therapy fails to achieve the expected goals

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