Levothyroxine Sodium

What it is and how it works

Mechanism of Action Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins. The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.

Indications

Hypothyroidism Levothyroxine sodium tablets are indicated in adult and pediatric patients, including neonates, as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. Pituitary Thyrotropin (Thyroid-Stimulating Hormone, TSH) Suppression Levothyroxine sodium tablets are indicated in adult and pediatric patients, including neonates, as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer. Limitations of Use • Levothyroxine sodium tablets are not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients as there are no clinical benefits and overtreatment with levothyroxine sodium tablets may induce hyperthyroidism . • Levothyroxine sodium tablets are not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.

Dosage and administration (summary)

• Administer once daily, preferably on an empty stomach, one-half to one hour before breakfast. • Administer at least 4 hours before or after drugs that are known to interfere with absorption. • Evaluate the need for dose adjustments when regularly administering within one hour of certain foods that may affect absorption. • Advise patients to stop biotin and biotin-containing supplements at least 2 days before assessing TSH and/or T4 levels. • Starting dose depends on a variety of factors, including age, body weight, cardiovascular status, and concomitant medications. Peak therapeutic effect may not be attained for 4 to 6 weeks.

Contraindications

Levothyroxine sodium tablets are contraindicated in patients with uncorrected adrenal insufficiency . • Uncorrected adrenal insufficiency.

Warnings and precautions

• Serious risks related to overtreatment or undertreatment with levothyroxine sodium tablet : Titrate the dose of levothyroxine sodium tablet carefully and monitor response to titration. . • Cardiac adverse reactions in the elderly and in patients with underlying cardiovascular disease: Initiate levothyroxine sodium tablet at less than the full replacement dose because of the increased risk of cardiac adverse reactions, including atrial fibrillation. ( 2.3 , 5.2 , 8.5 ) • Myxedema coma: Do not use oral thyroid hormone drug products to treat myxedema coma.

Pregnancy

Pregnancy Risk Summary The clinical experience, including data from postmarketing studies, in pregnant women treated with oral levothyroxine to maintain euthyroid state have not reported increased rates of major birth defects, miscarriages, or other adverse maternal or fetal outcomes.

Storage and supply

How Supplied Levothyroxine sodium tablets USP are round, colored, scored and debossed with following debossing details on one side and break-line on other side. They are supplied as follows: Strength (mcg) Color/Shape Debossing Details NDC# for bottles of 30 88 Olive/Round L19 82804-281-30 Storage and Handling Store at 25°C (77°F).

Source: Levothyroxine Sodium (Levothyroxine Sodium) — US FDA prescribing information, 2026-04-01, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.