L-Thyroxin-Na (Levothyroxine Sodium)

Levothyroxine Sodium is used in thyroid hormone replacement therapy to restore normal metabolic function.

• Hypothyroidism: restores normal thyroid hormone levels and alleviates symptoms such as fatigue, weight gain, and cold intolerance.
• Thyroid hormone replacement after thyroidectomy: provides the necessary thyroxine to maintain metabolic rate when the thyroid gland has been surgically removed.
• Goiter: helps reduce gland enlargement by normalizing thyroid hormone feedback mechanisms.
• Congenital hypothyroidism: ensures adequate thyroid hormone supply in newborns with absent or deficient thyroid function.

• Levothyroxine Sodium is a synthetic analogue of the endogenous thyroid hormone thyroxine (T4). After oral absorption, it is converted to the active hormone triiodothyronine (T3) within peripheral tissues. The hormone binds nuclear thyroid hormone receptors, modulating gene transcription that increases basal metabolic rate, promotes protein synthesis, and regulates growth and development. It also exerts negative feedback on pituitary thyroid‑stimulating hormone (TSH) secretion, helping to normalize TSH levels.

Levothyroxine Sodium may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Headache: mild to moderate headache that may occur especially after dose changes.
• Insomnia: difficulty falling asleep or staying asleep, often reported during therapy initiation.
• Palpitations: sensation of rapid or irregular heartbeat, usually transient.
• Nausea: mild gastrointestinal upset, often transient.
• Weight loss: unintended reduction in body weight, especially in overtreated patients.

Serious or Rare Side Effects

• Cardiac arrhythmia: potentially life‑threatening irregular heart rhythm that may require immediate medical attention.
• Hyperthyroidism symptoms: signs such as tremor, anxiety, heat intolerance, and increased sweating indicating overtreatment.
• Allergic reaction: rash, itching, swelling, or anaphylaxis that necessitates discontinuation of the drug.

Before prescribing Levothyroxine Sodium, clinicians should consider several precautionary measures to ensure safe and effective therapy.

• Dose adjustment: individualize dose based on age, weight, cardiac status, and thyroid function tests.
• Cardiovascular disease: monitor closely in patients with ischemic heart disease or arrhythmias.
• Pregnancy and lactation: assess risk‑benefit, as dosage may need adjustment during pregnancy.
• Drug interactions: review concomitant medications that may affect absorption or metabolism.
• Adherence: ensure patient takes medication consistently on an empty stomach, typically 30‑60 minutes before breakfast.
• Store at ambient temperature: keep tablets in original container, protect from moisture and light.

Levothyroxine Sodium interacts with several medicines that can alter its absorption, metabolism, or therapeutic effect.

Major Interactions (Avoid)

• Calcium or iron supplements: bind levothyroxine in the gut, markedly reducing its absorption.
• Antacids containing aluminum or magnesium: decrease levothyroxine bioavailability when taken simultaneously.
• Amiodarone: can cause excess thyroid hormone levels and requires dose adjustment.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect, necessitating INR monitoring.
• Beta‑blockers: may mask symptoms of hyperthyroidism, requiring careful clinical observation.
• SSRIs and tricyclic antidepressants: may affect thyroid hormone metabolism, warranting periodic thyroid function tests.