Best Practice & Research Clinical Endocrinology & Metabolism
8Conditions and drugs interfering with thyroxine absorption
Section snippets
Absorption of levothyroxine
Approximately 62–82% of levothyroxine is absorbed after oral administration. This absorption occurs within the first 3 h of ingestion and is localised mainly in the jejunum and ileum.1 The absorption of levothyroxine is maximal when the stomach is empty, reflecting the importance of gastric acidity in this process. Patients with jejunoileal bypass surgery or other bowel resection have been reported to require higher doses of levothyroxine following surgery.2, 3, 4 Stone et al. noted reduced peak
Food and dietary fibre
Absorption of levothyroxine has been shown to be influenced both by the timing of food intake and by certain foods. This was first reported by Wenzel et al. in their study comprising 37 patients.13 Subjects ingested either 100 μg or 3 mg of levothyroxine under two settings: (1) fasting, or (2) immediately before the consumption of two buttered rolls and a boiled egg. Using the double-isotope method developed by Hays, the authors showed that absorption was significantly better in the fasting state
Gastrointestinal disorders
Both malabsorptive disorders and conditions that impair gastric acidity can affect the bioavailability of levothyroxine. Early reports described elevated serum TSH levels in patients with coeliac sprue and inflammatory bowel disease despite thyroxine doses that had previously normalised serum levels. These findings suggest that pre-existing malabsorption can reduce the bioavailability of levothyroxine. This association appears to be strongest with coeliac disease. More recently, a study has
Medications
Several commonly used oral medications have been shown to alter the bioavailability of levothyroxine, many of which interfere by forming an insoluble or non-absorbable complex with levothyroxine.
Conclusion
Various endogenous and exogenous factors can change the absorption kinetics of levothyroxine. The timing of food intake in relation to levothyroxine administration is important, and it is recommended to delay food by at least 60 min following ingestion. Fibre and espresso coffee have been shown to interfere, indicating that the content of dietary intake is also important. Disorders of malabsorption or impaired gastric acidity can reduce the absorption of levothyroxine, and resistant
Conflict of interest
The authors have no conflicts of interest to declare.
References (45)
- et al.
Aspects of the absorption of oral L-thyroxine in normal man
Metabolism
(1977) - et al.
Sucralfate causes malabsorption of L-thyroxine
American Journal of Medicine
(1994) - et al.
Nonspecific intestinal adsorption of levothyroxine by aluminum hydroxide
American Journal of Medicine
(1994) - et al.
Effect of proton pump inhibitors on serum thyroid-stimulating hormone level in euthyroid patients treated with levothyroxine for hypothyroidism
Endocrine Practice
(2007) - et al.
Hypothyroidism in thyroid carcinoma follow-up: orlistat may inhibit the absorption of thyroxine
Clinical Oncology (Royal College of Radiologists (Great Britain))
(2005) - et al.
Delayed intestinal absorption of levothyroxine
Thyroid
(1995) - et al.
Malabsorption of thyroid hormones after jejunoileal bypass for obesity
Annals of Internal Medicine
(1979) - et al.
Increased requirement for thyroid hormone after a jejunoileal bypass operation
Canadian Medical Association Journal
(1980) - et al.
Thyroxine malabsorption following intestinal bypass surgery
International Journal of Obesity
(1986) - et al.
L-thyroxine absorption in patients with short bowel
The Journal of Clinical Endocrinology and Metabolism
(1984)
Decreased serum thyroid hormone levels and increased TSH response to TRH in infants with celiac disease
Clinical Endocrinology (Oxford)
Exaggerated levothyroxine malabsorption due to calcium carbonate supplementation in gastrointestinal disorders
Annals of Pharmacotherapy
Absorption of oral thyroxine in man
The Journal of Clinical Endocrinology and Metabolism
Absorption of oral thyroxine in hypothyroid and normal man
The Journal of Clinical Endocrinology and Metabolism
The bioavailability thyroxine and 3,5,3′-triiodothyronine in normal subjects and in hyper- and hypothyroid patients
Acta Endocrinologica (Copenh)
Non-isotopic method for determination of oral thyroxine absorption
Simultaneous measurement of thyroxine and triiodothyronine peripheral turnover kinetics in man
The Journal of Clinical Investigation
Evidence for a clinically important adverse effect of fiber-enriched diet on the bioavailability of levothyroxine in adult hypothyroid patients
The Journal of Clinical Endocrinology and Metabolism
Effects of pharmacological fiber supplements on levothyroxine absorption
Thyroid
Altered intestinal absorption of L-thyroxine caused by coffee
Thyroid
Gluten-induced enteropathy (coeliac disease) revealed by resistance to treatment with levothyroxine and alfacalcidol in a sixty-eight-year-old patient: a case report
Thyroid
Autoimmune hypothyroidism nonresponsive to high doses of levothyroxine and severe hypocalcemia
Arquivos Brasileiros de Endocrinologia e Metabologia
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2021, Journal of the Indian Chemical SocietyCitation Excerpt :A recent study assessed levothyroxine dosage along with drugs like sucralfate, cholestyramine and proton pump inhibitors and found that these drugs can impair levothyroxine absorption. These studies also proved that these drugs can affect levothyroxine metabolism [11–15]. The assessment of strength of molecular interaction of drug with enzymes and hormones and also understanding the mechanism of drug action will be helpful in drug design [16].
Levothyroxine dose adjustment in hypothyroid patients following gastric sleeve surgery
2020, Annales d'EndocrinologieCitation Excerpt :As not all patients received these treatments, and those that did were given different dosages and varying lengths of treatment, variations in absorption could well arise causing knock-on effects on levothyroxine dose. Certain digestive disorders can alter levothyroxine absorption: coeliac disease, gastritis, lactose intolerance and digestive tract inflammatory disease (Crohn) [28,31]. We do not have a record of such digestive pathologies in our study.