Oroxine (Levothyroxine Sodium Pentahydrate)

Levothyroxine is a synthetic thyroid hormone that acts on the hypothalamic‑pituitary‑thyroid axis to normalize hormone levels.

• Primary hypothyroidism: restores normal thyroid hormone concentrations and alleviates symptoms of low metabolism.
• Secondary (central) hypothyroidism: replaces deficient hormone when pituitary or hypothalamic dysfunction reduces endogenous production.
• Congenital hypothyroidism: provides essential hormone to infants with absent or impaired thyroid function.
• Thyroid cancer (post‑thyroidectomy) suppression therapy: suppresses TSH to reduce stimulation of residual thyroid tissue or tumor cells.

• Levothyroxine sodium pentahydrate is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it is converted to the active triiodothyronine (T3) within peripheral tissues. T3 binds nuclear thyroid hormone receptors, modulating gene transcription that regulates basal metabolic rate, protein synthesis, and development. By replenishing deficient hormone, it normalizes the feedback loop of the hypothalamic‑pituitary‑thyroid axis.

Levothyroxine may cause a range of adverse reactions, most of which are dose‑related.

Common Side Effects

• Headache: mild to moderate pain often resolves with dose adjustment.
• Insomnia: difficulty sleeping, especially if taken later in the day.
• Palpitations or tachycardia: rapid heartbeat sensation.
• Tremor: fine shaking of hands or limbs.
• Diarrhea: loose stools, usually transient.
• Heat intolerance: increased sensitivity to warm environments.

Serious or Rare Side Effects

• Angina or myocardial infarction: chest pain or heart attack in susceptible patients.
• Atrial fibrillation or other arrhythmias: irregular heart rhythm requiring medical attention.
• Osteoporosis or bone loss: long‑term excess may reduce bone density.
• Severe allergic reaction: rash, angioedema, or anaphylaxis.
• Adrenal insufficiency exacerbation: can precipitate adrenal crisis if untreated.

Levothyroxine requires careful monitoring and individualized dosing.

• Dose adjustment: regularly assess TSH and free T4 levels to fine‑tune the dose.
• Cardiovascular disease: use caution in patients with coronary artery disease or arrhythmias.
• Elderly patients: start with a lower dose due to increased sensitivity and reduced clearance.
• Pregnancy: monitor thyroid function closely; dose may need upward adjustment.
• Drug interactions: review concomitant medications that may affect absorption or metabolism.
• Store at room temperature: keep in the original container, protect from moisture and light.

Levothyroxine absorption and activity can be altered by several medicines.

Major Interactions (Avoid)

• Calcium or iron supplements: significantly reduce levothyroxine absorption when taken simultaneously.
• Antacids containing aluminum or magnesium: interfere with gastrointestinal uptake.
• Amiodarone: may cause thyroid hormone level fluctuations.
• Warfarin: levothyroxine can enhance anticoagulant effect, increasing bleeding risk.

Moderate Interactions (Monitor Closely)

• Cholestyramine or other bile‑acid sequestrants: decrease serum levothyroxine concentrations.
• Beta‑blockers: may mask symptoms of hyperthyroidism.
• Corticosteroids: can increase the metabolic clearance of levothyroxine.