Levothyroxine Aristo (Levothyroxine Sodium)

Levothyroxine is a synthetic thyroid hormone that acts on the hypothalamic‑pituitary‑thyroid axis to restore normal metabolic function. It is indicated for:

• Hypothyroidism: normalizes low thyroid hormone levels and alleviates associated symptoms.
• Thyroid hormone replacement therapy: provides a stable source of T4 for patients after thyroidectomy or radioactive iodine treatment.
• Goiter: reduces thyroid gland enlargement by correcting hormone deficiency.

• Levothyroxine is a synthetic form of thyroxine (T4) that is absorbed from the gastrointestinal tract and enters systemic circulation. It binds to nuclear thyroid hormone receptors, regulating gene transcription that controls basal metabolic rate, protein synthesis, and growth. By restoring circulating T4, the drug is converted to the active triiodothyronine (T3) in peripheral tissues, thereby normalizing metabolic activity across organ systems.

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

Common Side Effects

• Headache: mild to moderate intensity.
• Palpitations: sensation of rapid or irregular heartbeat.
• Weight loss: unintended reduction in body weight.
• Heat intolerance: increased sensitivity to warm environments.
• Tremor: fine shaking of hands or limbs.

Serious or Rare Side Effects

• Cardiac arrhythmia: potentially life‑threatening rhythm disturbances.
• Osteoporosis: decreased bone mineral density with long‑term overtreatment.
• Acute adrenal insufficiency: precipitated in patients with underlying adrenal disease.
• Allergic reaction: rash, itching, or swelling.
• Myopathy: muscle pain or weakness.

Levothyroxine requires careful monitoring and individualized dosing to avoid over‑ or under‑replacement.

• Dose adjustment: titrate based on serum TSH and free T4 levels.
• Monitor thyroid function: check labs every 6–8 weeks after dose changes.
• Avoid abrupt discontinuation: may cause hypothyroid rebound symptoms.
• Use with caution in cardiac disease: risk of angina or arrhythmias.
• Store at room temperature: keep in the original pack, protect from moisture.

Levothyroxine absorption and metabolism can be altered by several concomitant medications.

Major Interactions (Avoid)

• Calcium supplements: reduce levothyroxine absorption.
• Iron salts: decrease oral bioavailability.
• Antacids containing aluminum or magnesium: impair absorption.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect, requiring INR monitoring.
• Amiodarone: can affect thyroid hormone levels and require dose adjustment.
• Rifampin: induces hepatic enzymes, potentially increasing levothyroxine clearance.