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Levothyroxine

Generic Name
Levothyroxine
Brand Names
Eltroxin, Ermeza, Euthyrox, Levo-T, Levothroid, Levoxyl, Np Thyroid, Synthroid, Thyquidity, Tirosint, Unithroid
Drug Type
Small Molecule
Chemical Formula
C15H11I4NO4
CAS Number
51-48-9
Unique Ingredient Identifier
Q51BO43MG4
Background

Levothyroxine is a synthetically produced form of thyroxine, a major endogenous hormone secreted by the thyroid gland. Also known as L-thyroxine or the brand name product Synthroid, levothyroxine is used primarily to treat hypothyroidism, a condition where the thyroid gland is no longer able to produce sufficient quantities of the thyroid hormones T (tetraiodothyronine or thyroxine) and T (triiodothyronine or Liothyronine), resulting in diminished down-stream effects of these hormones. Without sufficient quantities of circulating thyroid hormones, symptoms of hypothyroidism begin to develop such as fatigue, increased heart rate, depression, dry skin and hair, muscle cramps, constipation, weight gain, memory impairment, and poor tolerance to cold temperatures.

In response to Thyroid Stimulating Hormone (TSH) release by the pituitary gland, a normally functioning thyroid gland will produce and secrete T, which is then converted through deiodination (by type I or type II 5′-deiodinases) into its active metabolite T. While T is the major product secreted by the thyroid gland, T exerts the majority of the physiological effects of the thyroid hormones; T and T have a relative potency of ~1:4 (T4:T3). T and T act on nearly every cell of the body, but have a particularly strong effect on the cardiac system. As a result, many cardiac functions including heart rate, cardiac output, and systemic vascular resistance are closely linked to thyroid status.

Prior to the development of levothyroxine, Thyroid, porcine or desiccated thyroid, used to be the mainstay of treatment for hypothyroidism. However, this is no longer recommended for the majority of patients due to several clinical concerns including limited controlled trials supporting its use. Desiccated thyroid products contain a ratio of T4 to T3 of 4.2:1, which is significantly lower than the 14:1 ratio of secretion by the human thyroid gland. This higher proportion of T3 in desiccated thyroid products can lead to supraphysiologic levels of T3 which may put patients at risk of thyrotoxicosis if thyroid extract therapy is not adjusted according to the serum TSH.

Indication

Levothyroxine is indicated as replacement therapy in primary (thyroidal), secondary (pituitary) and tertiary (hypothalamic) congenital or acquired hypothyroidism. It is also indicated as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.

Associated Conditions
Edematous Fibrosclerotic Panniculopathy (Cellulite), Hypothyroidism, Localized Adiposity, Myxedema coma, Euthyroid Goitre, Thyrotropin dependent Well-Differentiated Thyroid Cancer
Clinical Trials
Related News

Levothyroxine Trial to Evaluate Cardiovascular Benefits in Elderly with Subclinical Hypothyroidism

• A new multicenter, open-label randomized controlled trial will assess whether levothyroxine therapy can reduce cardiovascular disease risk in older adults with subclinical hypothyroidism using age-specific TSH reference values. • The 48-week study will measure changes in carotid intima-media thickness as a primary endpoint, with secondary outcomes including cardiovascular events, lipid profiles, and bone mineral density. • This groundbreaking research addresses limitations of previous studies by using age-appropriate diagnostic criteria for subclinical hypothyroidism in elderly patients from iodine-adequate regions in China.

FDA Approves Xeris Biopharma's Gvoke VialDx as First Ready-to-Dilute Liquid Glucagon for Gastrointestinal Diagnostics

• The FDA has approved Xeris Biopharma's Gvoke VialDx as a diagnostic aid to temporarily inhibit gastrointestinal tract movement during radiologic examinations in adult patients. • Xeris has partnered with American Regent for commercialization, with Xeris handling product supply and American Regent managing U.S. market distribution, targeting availability in Q3 2025. • As the first concentrated, ready-to-dilute liquid glucagon for diagnostic procedures, Gvoke VialDx aims to modernize administration in the growing procedural gastroenterology market, which performs an estimated 20 million endoscopic procedures annually.

Weight Loss from GLP-1 Drugs Regained After Discontinuation, Studies Show

• Clinical trials indicate that weight loss achieved with GLP-1 drugs like semaglutide and tirzepatide is often regained after patients stop taking the medication. • Studies such as the Step 1 trial extension and Surmount-4 trial demonstrate significant weight regain despite initial success with GLP-1 agonists. • Experts emphasize that obesity should be treated as a chronic disease, requiring long-term management strategies, similar to hypertension or hyperlipidemia. • Strategies to maintain weight loss after discontinuing GLP-1 drugs are lacking, highlighting the need for individualized approaches and further research.

Resmetirom Shows Promise in Treating MASLD/MASH: A Comprehensive Review of Clinical Trials

• Resmetirom, a β-selective thyromimetic, is the first FDA-approved drug for moderate to advanced MASH-fibrosis, demonstrating histological MASH resolution and fibrosis improvement. • Clinical trials, including MAESTRO-NASH and MAESTRO-NAFLD-1, have shown resmetirom's efficacy in reducing hepatic fat content and improving atherogenic biomarkers in MASLD/MASH patients. • Resmetirom was generally well-tolerated, with the most common adverse events being mild to moderate diarrhea and nausea, particularly in the initial weeks of treatment. • Ongoing trials, such as MAESTRO-NASH-OUTCOMES, are investigating resmetirom's long-term effects in patients with MASH-cirrhosis, evaluating disease progression and hepatic decompensation events.

Levothyroxine Use Linked to Bone Density Loss in Older Adults with Normal Thyroid Function

• A new study reveals that levothyroxine use is associated with bone density loss in older adults, even when thyroid function is within the normal range. • The research included 81 levothyroxine users and 364 non-users, with a median age of 73, monitored over a median of 6.3 years. • Findings suggest a need for careful risk-benefit assessment of levothyroxine treatment in older adults, considering potential adverse effects on bone health. • Regular monitoring of thyroid function is recommended for individuals taking levothyroxine to mitigate potential bone loss.

mHealth Intervention Improves Mental Health in Thyroid Cancer Patients

• A mobile health (mHealth) intervention based on the Multi-Theory Model (MTM) significantly reduced anxiety and depression in patients with differentiated thyroid cancer (DTC). • The study, a single-blind, randomized controlled trial, showed improved mental health outcomes with a personalized mHealth program delivered via WeChat. • The mHealth intervention included online health education, comprehensive medical care, and MTM-based content, enhancing patient self-management and emotional well-being. • These findings suggest that mHealth interventions can be a valuable tool for supporting DTC patients' psychological health during and after treatment.

Immunovant's Batoclimab Shows Promise in Graves' Disease Phase II Trial; IMVT-1402 Pivotal Trial Planned

• Immunovant's batoclimab demonstrated a 76% response rate in Graves' disease patients uncontrolled on antithyroid drugs (ATDs) after 12 weeks of high-dose treatment. • A 56% ATD-free response rate was achieved with high-dose batoclimab, indicating potential for patients to taper off their existing medication. • Immunovant plans to initiate a pivotal trial for IMVT-1402 in Graves' disease by the end of the year, following FDA clearance of the IND application. • Analysis suggests 25-30% of Graves’ disease patients remain uncontrolled on ATDs, representing a significant commercial opportunity.

Resmetirom: Duke Research Leads to First FDA-Approved Drug for MASH Liver Disease

• Resmetirom, a novel drug developed with Duke University research, has gained FDA approval as the first treatment for metabolic dysfunction-associated steatohepatitis (MASH). • The drug targets thyroid hormone pathways to stimulate fat breakdown in the liver, addressing a critical need for the estimated 115 million people worldwide affected by MASH. • While only 30% of trial participants benefited after one year and the treatment costs $50,000 annually, resmetirom marks a significant advancement, with hopes for expanded treatment options and reduced costs through further research. • Research indicates that interest in MASH is growing, with resmetirom and similar drugs potentially working alongside other therapies to combat the disease and alleviate the health burden associated with advanced liver and cardiovascular complications.

Iovance's MDA-TIL Trial Terminated, Sention's ST-1891 Phase II Completed

• Iovance Biotherapeutics' MDA-TIL Phase II trial was terminated due to lack of efficacy, significantly decreasing its Phase Transition Success Rate (PTSR) in ovarian, colorectal, and pancreatic cancers. • Sention Therapeutics' ST-1891 Phase II trial in hypothyroidism was completed, leading to a nine-point increase in the drug's PTSR, reaching 22% for this indication. • Karyopharm Therapeutics' Xpovio (selinexor) Phase II trial in metastatic melanoma was terminated due to insufficient anti-tumor activity, resulting in a 14-point PTSR decrease to 11%. • Armata Pharmaceuticals' APPA-02 Phase II trial in bronchiectasis was completed, increasing the drug candidate’s PTSR by seven points to 43%.
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