Letrox (Levothyroxine Sodium, Hydrate)

Letrox (levothyroxine sodium) is used to treat disorders of thyroid hormone deficiency.

• Hypothyroidism: restores normal thyroid hormone levels, alleviating fatigue, weight gain, cold intolerance, and metabolic slowdown.
• Post‑thyroidectomy hormone replacement: supplies necessary thyroxine after surgical removal of the thyroid gland to maintain metabolic balance.
• Goiter: reduces thyroid‑stimulating hormone drive, helping to shrink an enlarged thyroid and prevent further growth.
• Congenital hypothyroidism: provides essential hormone to infants born with insufficient thyroid function, supporting normal growth and neurodevelopment.

• Levothyroxine sodium is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it is converted to the active hormone triiodothyronine (T3) in peripheral tissues, binding to nuclear thyroid hormone receptors and regulating gene transcription. This restores normal metabolic processes, thermogenesis, and protein synthesis in cells that depend on thyroid hormone signaling.

Levothyroxine sodium may cause adverse reactions, which are categorized by frequency and severity.

Common Side Effects

• Headache: mild to moderate discomfort often reported during dose adjustments.
• Insomnia: difficulty sleeping, especially if taken later in the day.
• Palpitations: sensation of rapid or irregular heartbeat.
• Heat intolerance: increased sensitivity to warm environments.
• Tremor: fine shaking of hands or limbs.
• Weight loss: unintended reduction in body weight.

Serious or Rare Side Effects

• Cardiac arrhythmia: irregular heart rhythm that may require medical attention.
• Angina or myocardial infarction: chest pain or heart attack, particularly in patients with pre‑existing heart disease.
• Osteoporosis or bone loss: decreased bone mineral density with long‑term overtreatment.
• Severe allergic reaction: rash, itching, swelling, or difficulty breathing.
• Adrenal insufficiency: exacerbation of underlying adrenal disorders.
• Hyperthyroid symptoms: excessive hormone levels causing anxiety, sweating, or tremor.

When prescribing Letrox, clinicians should consider several safety measures.

• Dose adjustment: titrate based on thyroid function tests and clinical response to avoid over‑ or under‑replacement.
• Cardiovascular monitoring: assess for tachycardia, angina, or arrhythmias, especially in patients with heart disease.
• Pregnancy and lactation: use only if benefits outweigh risks; consult a physician before initiating therapy.
• Drug interactions: review concomitant medications that may affect absorption or metabolism of levothyroxine.
• Store at ambient temperature: keep below 25 °C, in the original container, protected from moisture and light.

Levothyroxine sodium can interact with several medicines, requiring attention to timing and monitoring.

Major Interactions (Avoid)

• Calcium or iron supplements: significantly reduce levothyroxine absorption; separate dosing by at least 4 hours.
• Antacids containing aluminum or magnesium: impair absorption; avoid concurrent administration.
• Amiodarone: may alter thyroid hormone levels; requires close monitoring.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect; monitor INR regularly.
• Corticosteroids: may increase hormone metabolism; dose adjustment may be needed.
• SSRIs (e.g., sertraline): may affect thyroid function tests; observe clinical response and adjust if necessary.