Levothyroxine Abdi (Levothyroxine Sodium)

Levothyroxine is a synthetic thyroid hormone used to treat conditions related to thyroid hormone deficiency.

• Hypothyroidism: restores normal thyroid hormone levels, relieving fatigue, weight gain, and cold intolerance.
• Goiter: reduces thyroid‑stimulating hormone drive, helping to shrink an enlarged thyroid gland.
• Thyroid hormone replacement after thyroidectomy or radioactive iodine therapy: maintains metabolic stability when the gland is absent or non‑functional.
• Thyroid cancer suppression: provides hormone levels that suppress TSH, reducing stimulation of residual cancer cells.
• Congenital hypothyroidism in infants: ensures adequate thyroid hormone for normal growth and neurodevelopment.

• Levothyroxine is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it is converted by peripheral deiodinases to the active hormone triiodothyronine (T3), which binds nuclear thyroid hormone receptors (TRα and TRβ). Receptor activation modulates transcription of genes involved in basal metabolic rate, protein synthesis, and growth, thereby restoring normal physiological functions in patients with deficient thyroid hormone production.

Levothyroxine may cause a range of adverse reactions, varying from mild to severe, depending on individual sensitivity and dosage.

Common Side Effects

• Headache: mild to moderate headache occurring after dose adjustments.
• Palpitations: sensation of rapid or irregular heartbeat, often transient.
• Tremor: fine shaking of hands or limbs, especially at higher doses.
• Gastrointestinal upset: nausea, abdominal cramps, or constipation.
• Insomnia: difficulty falling or staying asleep.
• Weight gain: mild increase in body weight, especially at initiation.

Serious or Rare Side Effects

• Cardiac arrhythmia: potentially life‑threatening irregular heart rhythm.
• Hyperthyroidism symptoms: excessive sweating, weight loss, anxiety, or heat intolerance.
• Bone loss: accelerated osteoporosis with long‑term overtreatment.
• Angina pectoris: chest pain due to increased myocardial oxygen demand.
• Severe allergic reaction: rash, itching, swelling, or anaphylaxis.

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

• Dose titration: adjust the dose based on thyroid function tests and clinical response.
• Drug interactions: review concomitant medications that may affect absorption or metabolism.
• Cardiovascular status: monitor patients with heart disease for signs of tachycardia or angina.
• Pregnancy and lactation: use only if clearly needed, as thyroid hormone requirements may change.
• Elderly patients: start with lower doses and monitor for overtreatment.
• Store at ambient temperature: keep below 25°C in the original container, protect from moisture and light.

Levothyroxine can interact with other agents that influence its absorption, distribution, or thyroid hormone activity.

Major Interactions (Avoid)

• Calcium or iron supplements: co‑administration reduces levothyroxine absorption; separate dosing by at least 4 hours.
• Antacids containing aluminum or magnesium: markedly decrease absorption; avoid concurrent use.
• Sevelamer: binds levothyroxine in the gut, significantly reducing its bioavailability; avoid co‑administration.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect; monitor INR closely.
• Beta‑blockers: may mask symptoms of hyperthyroidism; observe heart rate and blood pressure.
• Amiodarone: alters thyroid hormone metabolism; check thyroid function tests regularly.
• Cholestyramine: may decrease absorption; monitor thyroid levels.
• Oral contraceptives: may increase thyroid‑binding globulin, requiring dose adjustment.