Effect of Calcium Carbonate on the Absorption of Levothyroxine
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TLDR
This study of 20 patients receiving long-term levothyroxine replacement therapy indicates that calcium carbonate reduces T(4) absorption and increases serum thyrotropin levels.Abstract:
ContextThe effect of calcium carbonate on the absorption of levothyroxine has
not been studied systematically. Such a potential drug interaction merits
investigation because concurrent treatment with both drugs is common, particularly
in postmenopausal women.ObjectiveTo investigate the potential interference of calcium carbonate in the
absorption of levothyroxine.DesignProspective cohort study conducted from November 1998 to June 1999,
supplemented with an in vitro study of thyroxine (T4) binding to
calcium carbonate.SettingVeterans Affairs Medical Center in West Los Angeles, Calif.PatientsTwenty patients (age range, 27-78 years; n=11 men) with hypothyroidism
who were taking a stable long-term regimen of levothyroxine were included
in the study. All patients had serum free T4 and thyrotropin values
in the normal range before beginning the study.InterventionSubjects were instructed to take 1200 mg/d of elemental calcium as calcium
carbonate, ingested with their levothyroxine, for 3 months.Main Outcome MeasuresLevels of free T4, total T4, total triiodothyronine
(T3), and thyrotropin, measured in all subjects at baseline (while
taking levothyroxine alone), at 2 and 3 months (while taking calcium carbonate
and levothyroxine), and 2 months after calcium carbonate discontinuation (while
continuing to take levothyroxine).ResultsMean free T4 and total T4 levels were significantly
reduced during the calcium period and increased after calcium discontinuation.
Mean free T4 levels were 17 pmol/L (1.3 ng/dL) at baseline, 15
pmol/L (1.2 ng/dL) during the calcium period, and 18 pmol/L (1.4 ng/dL) after
calcium discontinuation (overall P<.001); mean
total T4 levels were 118 nmol/L (9.2 µg/dL) at baseline,
111 nmol/L (8.6 µg/dL) during the calcium period, and 120 nmol/L (9.3
µg/dL) after calcium discontinuation (overall P=.03).
Mean thyrotropin levels increased significantly, from 1.6 mIU/L at baseline
to 2.7 mIU/L during the calcium period, and decreased to 1.4 mIU/L after calcium
discontinuation (P=.008). Twenty percent of patients
had serum thyrotropin levels higher than the normal range during the calcium
period; the highest observed level was 7.8 mIU/L. Mean T3 levels
did not change during the calcium period. The in vitro study of T4
binding to calcium showed that adsorption of T4 to calcium carbonate
occurs at acidic pH levels.ConclusionsThis study of 20 patients receiving long-term levothyroxine replacement
therapy indicates that calcium carbonate reduces T4 absorption
and increases serum thyrotropin levels. Levothyroxine adsorbs to calcium carbonate
in an acidic environment, which may reduce its bioavailability.read more
Citations
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Journal ArticleDOI
Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement
Jacqueline Jonklaas,Antonio C. Bianco,Andrew J. Bauer,Kenneth D. Burman,Anne R. Cappola,Francesco S. Celi,David S. Cooper,Brian W. Kim,Robin P. Peeters,M. Sara Rosenthal,Anna M. Sawka +10 more
TL;DR: It is concluded that levothyroxine should remain the standard of care for treating hypothyroidism and no consistently strong evidence for the superiority of alternative preparations is found.
Journal ArticleDOI
Drugs in Pregnancy
TL;DR: For example, this article found that most drugs that appear in the Physicians' Desk Reference and similar sources contain statements such as, “Use in pregnancy is not recommended unless the potential benefits justify the potential risks to the fetus.
Journal ArticleDOI
Thyroxine in goiter, Helicobacter pylori infection, and chronic gastritis.
Marco Centanni,Lucilla Gargano,Gianluca Canettieri,N Viceconti,Antonella Franchi,Gianfranco Delle Fave,Bruno Annibale +6 more
TL;DR: Patients with impaired acid secretion require an increased dose of thyroxine, suggesting that normal gastric acid secretion is necessary for effective absorption of oral thyrotropin.
Journal ArticleDOI
American Thyroid Association Statement on Postoperative Hypoparathyroidism: Diagnosis, Prevention, and Management in Adults
Lisa A. Orloff,Sam M. Wiseman,Victor Bernet,Fahey Tj rd,Ashok R. Shaha,Maisie L. Shindo,Samuel K. Snyder,Brendan C. Stack,John B. Sunwoo,Marilene B. Wang +9 more
TL;DR: Effective management of mild to moderate potential or actual postoperative hypoPT can be achieved by administering either empiric/prophylactic oral calcium and vitamin D, selective oral calcium, and Vitamin D based on rapid postoperative PTH level(s), or serial serum calcium levels as a guide.
Journal ArticleDOI
Conditions and drugs interfering with thyroxine absorption.
TL;DR: Many commonly used drugs, such as bile acid sequestrants, ferrous sulphate, sucralfate, calcium carbonate, aluminium-containing antacids, phosphate binders, raloxifene and proton-pump inhibitors, have also been shown to interfere with the absorption of levothyroxine.
References
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Journal ArticleDOI
Delayed intestinal absorption of levothyroxine.
TL;DR: Full suppression or normalization of TSH is obtained by postponing breakfast for at least 60 min after T4 ingestion by patients in whom TSH-suppressive or replacement L-T4 therapy failed to suppress or normalize serum TSH.
Journal ArticleDOI
The Influence of Cholestyramine on Thyroxine Absorption
TL;DR: Hypothyroid patients receiving cholestyramine should be examined periodically for evidence of hypothyroidism, and adjustments in dose and time interval between the two agents should be made if malabsorption of thyroid hormone is significant.
Journal ArticleDOI
Evidence for a clinically important adverse effect of fiber-enriched diet on the bioavailability of levothyroxine in adult hypothyroid patients.
TL;DR: Results indicate a decrease in T4 bioavailability by dietary fiber through a mechanism involving nonspecific adsorption of T4 to dietary fibers, which may account for the need for larger than expected doses of T 4 in some hypothyroid patients.
Journal ArticleDOI
Localization of human thyroxine absorption.
TL;DR: The distribution of intestinal absorption of 131I-labeled thyroxine (T4*) was studied in normal subjects after oral and i.v. T4*, and model projections mimicking clinical gut abnormalities known to affect T4 absorption were compatible with the results of published studies.
Journal ArticleDOI
Sucralfate Causes Malabsorption of L-Thyroxine
TL;DR: Sucralfate causes malabsorption of L-thyroxine, presumably by intraluminal binding of hormone, and maximum T3 levels did not differ, regardless of drug regimen, but suppression of thyroid-stimulating hormone (TSH) by L- thyroxine was reduced by coadministration of sucralfates.