What is the proper administration of levothyroxine (T4)?

From the Guidelines

Levothyroxine should be taken once daily in the morning, on an empty stomach, 30-60 minutes before breakfast with a full glass of water. The typical starting dose ranges from 25-100 mcg daily, depending on age, weight, and severity of hypothyroidism, as the principal treatment for hypothyroidism is oral T4 monotherapy (levothyroxine sodium) 1. Take the medication consistently at the same time each day to maintain stable blood levels.

Important Considerations

• Avoid taking levothyroxine with calcium supplements, iron supplements, antacids, or foods high in fiber or soy, as these can interfere with absorption.
• Wait at least 4 hours after taking levothyroxine before taking these substances.
• Certain medications like proton pump inhibitors, cholestyramine, and some seizure medications can also affect levothyroxine absorption or effectiveness, so inform your doctor about all medications you take.

Dosage Adjustment

• In grade >2 IR-hypothyroidism, hormone replacement therapy (levothyroxine 50-100 mg/day) should be started in symptomatic cases, and the dose should be increased over several weeks until thyroid-stimulating hormone levels normalize 1.

Monitoring

• Regular blood tests (typically every 6-8 weeks initially, then every 6-12 months) are necessary to monitor thyroid levels and adjust dosage as needed.
• The serum TSH test is the primary screening test for thyroid dysfunction, and multiple tests should be done over a 3- to 6-month interval to confirm or rule out abnormal findings 1.

From the FDA Drug Label

2 DOSAGE AND ADMINISTRATION

1. 1 Important Administration Instructions Administer levothyroxine sodium tablets as a single daily dose, on an empty stomach, one-half to one hour before breakfast with a full glass of water to avoid choking or gagging Administer levothyroxine sodium tablets at least 4 hours before or after drugs known to interfere with levothyroxine sodium absorption

To take levothyroxine:

• Administer as a single daily dose, on an empty stomach, one-half to one hour before breakfast with a full glass of water.
• Take at least 4 hours before or after drugs known to interfere with levothyroxine sodium absorption.
• For patients who cannot swallow intact tablets, crush the tablet, suspend in a small amount of water, and administer immediately.
• Do not administer in foods that decrease absorption, such as soybean-based infant formula 2.

From the Research

Administration of Levothyroxine

• Levothyroxine (LT4) is a safe and effective means of hormone replacement therapy for hypothyroidism 3.
• The absorption of LT4 can be reduced or slowed by factors that alter the state of the epithelium in the stomach or small intestine, such as ulcerative colitis, coeliac disease, bariatric surgery, Helicobacter pylori infection, food intolerance, gastritis, mineral supplements, dietary fibre, resins, and various drugs 3.
• LT4 is almost fully bound to plasma proteins once in the circulation, and changes in plasma protein levels can modify free hormone levels 3.

Dosage and Replacement Therapy

• The standard of care for overt hypothyroidism is levothyroxine at doses that normalize serum TSH levels 4.
• Weekly levothyroxine replacement may be a suitable alternative for non-adherent patients, resulting in less suppression and higher mean serum TSH levels while still remaining within the normal reference range 5.
• Synthetic LT4, titrated to bring the level of TSH within a predefined "normal" reference range, is now established as the mainstay of treatment for hypothyroidism, and provides adequate restoration of thyroid hormone function for most people with this condition 6.

Monitoring and Adjustment

• Clinicians should review medications, medical history, and serum FT4 levels, and check for acute adrenal insufficiency, heterophilic anti-TSH antibodies, and Helicobacter pylori infection in patients with abnormally high TSH levels 3.
• An LT4 pharmacodynamic absorption test may be necessary to assess poor LT4 absorption, and consultation with a gastroenterologist may be required to increase the LT4 dose level 3.
• Normalizing serum TSH levels in hypothyroid patients can reduce the risk of death, with an estimated reduction of 28.3 million people in the USA and Europe alone 7.