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Levothyroxine

Thyroid Hormones
T4SynthroidEuthyroxL-Thyroxine

Overview

Levothyroxine, also known as T4, Synthroid, or Euthyrox, is a synthetic form of the endogenous thyroid hormone thyroxine. It is produced by the thyroid gland and belongs to the class of hormones known as thyroid hormones. As a synthetic compound, levothyroxine is used to supplement or replace endogenous thyroxine in individuals with thyroid hormone deficiencies. It is chemically classified as a tetraiodothyronine, containing four iodine atoms. Researchers have extensively studied levothyroxine for its role in regulating metabolism and energy balance. The primary physiological roles of levothyroxine include the regulation of metabolic rate, heart and digestive function, muscle control, brain development, and bone maintenance. Research areas include its impact on metabolic disorders, cardiovascular health, and neurodevelopmental conditions. Levothyroxine acts primarily through binding to thyroid hormone receptors, which are nuclear receptors that modulate gene expression. Upon binding, it influences the transcription of genes involved in metabolic processes, growth, and development. This action initiates a biological cascade that affects various physiological systems, including the cardiovascular and nervous systems. Pharmacokinetically, levothyroxine has a long half-life of approximately 6-7 days, allowing for once-daily dosing. It is metabolized primarily in the liver and kidneys, with a bioavailability of about 40-80% when administered orally, depending on factors such as gastrointestinal pH and the presence of food. Clinically, levothyroxine is used to treat hypothyroidism and is approved by regulatory agencies worldwide. It is considered a standard treatment for thyroid hormone replacement therapy and is available by prescription. Researchers have found it to be effective in restoring normal thyroid hormone levels and alleviating symptoms of hypothyroidism.

Mechanism of Action

Levothyroxine acts on thyroid hormone receptors, primarily TRα and TRβ, which are nuclear receptors that regulate gene expression. This interaction leads to the modulation of genes involved in metabolic processes, influencing energy expenditure, growth, and development.

Molecular Data

FormulaC15H11I4NO4
Molecular Weight776.87 g/mol
CAS Number51-48-9
PubChem CID5819

Half-Life & Pharmacokinetics

EndogenousCirculating half-life ~6-7 days
OralBioavailability ~40-80%, influenced by gastrointestinal factors

The half-life allows for once-daily dosing; absorption can be affected by food and other medications.

Storage

Temperature

Store at room temperature (15-30°C)

Light

Protect from light

Form

Tablets are stable for several years if stored properly

Notes

Avoid exposure to moisture; keep in original packaging until use.

Solubility

Levothyroxine is poorly soluble in water but soluble in ethanol, which is relevant for certain formulations.

Legal Status

🇩🇪DE

Prescription only (verschreibungspflichtig), not a controlled substance under BtMG.

🇺🇸US

FDA approved for hypothyroidism treatment, prescription required.

🇦🇺AU

TGA Schedule 4 (S4), prescription only medicine.

🇬🇧UK

Prescription only medicine (POM) under MHRA regulations.

Legal status information is provided for general reference only and may not reflect the most current regulatory changes. Always verify with official government sources before making any decisions.

5 Research Publications

Hypothyroidism and metabolic cardiovascular disease.

Review

Frontiers in endocrinology · 2024

Researchers observed that both hypothyroidism and cardiovascular disease (CVD) are common and linked, potentially increasing the risk of heart-related issues. They found that treating subclinical hypothyroidism with levothyroxine may benefit younger patients, but the effects in older adults remain unclear, highlighting the need for more research in this area.

  • Hypothyroidism can contribute to the development and worsening of cardiovascular disease.
  • Younger patients with subclinical hypothyroidism may benefit from treatment with levothyroxine.
  • The effectiveness of treatment in older adults with subclinical hypothyroidism is still debated.
PubMed

Acquired Hypothyroidism in Children.

Review

Indian journal of pediatrics · 2023

Researchers observed that acquired hypothyroidism, often seen in children aged 9 to 11, can lead to symptoms like poor growth and fatigue. Many affected children show no symptoms at diagnosis, and treatment typically involves hormone replacement therapy with levothyroxine, requiring regular monitoring for effective management.

  • Acquired hypothyroidism is common in children aged 9-11 and rare before age 4.
  • Approximately 80% of diagnosed children are asymptomatic.
  • Treatment involves levothyroxine, with careful monitoring needed for proper growth and development.
PubMed

Levothyroxine Interactions with Food and Dietary Supplements-A Systematic Review.

Meta-Analysis

Pharmaceuticals (Basel, Switzerland) · 2021

Researchers found that levothyroxine, a medication for hypothyroidism, can interact with certain foods and supplements, affecting its absorption. They observed that taking levothyroxine in the morning or at bedtime is equally effective, but specific foods like coffee and calcium may reduce its effectiveness. Proper timing between taking levothyroxine and consuming these items can help improve treatment outcomes.

  • Levothyroxine can be taken in the morning or at bedtime with equal effectiveness.
  • Certain foods and supplements, like coffee and calcium, can decrease levothyroxine absorption.
  • Maintaining a time gap between levothyroxine and food intake can help avoid interactions.
PubMed

Levothyroxine Therapy in Elderly Patients With Hypothyroidism.

Review

Frontiers in endocrinology · 2021

Researchers observed that treating hypothyroidism in elderly patients with levothyroxine can be more complicated due to their higher likelihood of heart issues and other health conditions. They found that careful monitoring and collaboration with cardiologists are essential to ensure safe and effective treatment.

  • Elderly patients often have more comorbidities, complicating hypothyroidism management.
  • Lower doses of levothyroxine may be needed to avoid heart complications.
  • Diagnosis of mild hypothyroidism in the elderly is challenging and requires careful evaluation.
PubMed

Congenital hypothyroidism.

Review

Indian journal of endocrinology and metabolism · 2015

Researchers observed that congenital hypothyroidism (CH) is a common condition that can lead to intellectual disabilities if not diagnosed early. They emphasized the importance of newborn screening to detect CH, as timely treatment can significantly improve developmental outcomes.

  • CH is primarily caused by abnormal thyroid gland development, accounting for 85% of cases.
  • Early screening using dried blood samples from newborns is crucial for timely diagnosis.
  • Prompt treatment with levothyroxine can help achieve normal growth and cognitive development.
PubMed

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This page is for informational and research purposes only. All information is based on published scientific literature. Nothing on this page constitutes medical advice or replaces consultation with a qualified healthcare professional.