Levothyroxinenatrium Aristo (Anhydrous Levothyroxine Sodium)

• Levothyroxine is used to replace deficient thyroid hormone in several clinical conditions.
• Hypothyroidism: restores normal hormone levels to relieve fatigue, weight gain and cold intolerance.
• Post‑thyroidectomy: provides necessary thyroid hormone after surgical removal of the gland.
• Congenital hypothyroidism: ensures adequate hormone supply for growth and development in newborns.
• Goiter: helps normalize thyroid function and may reduce gland enlargement.

• Levothyroxine is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption it is converted to the active triiodothyronine (T3) within cells. The hormone binds nuclear thyroid hormone receptors, modulating transcription of target genes that regulate basal metabolic rate, protein synthesis and development. By restoring circulating T4 levels, it normalizes the hypothalamic‑pituitary‑thyroid feedback loop and stabilizes metabolic processes.

Levothyroxine may cause a range of adverse reactions, varying in frequency and severity.

Common Side Effects

• Headache: mild to moderate pain in the head.
• Insomnia: difficulty falling or staying asleep.
• 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 the hands.

Serious or Rare Side Effects

• Arrhythmia: abnormal heart rhythm that may be life‑threatening.
• Angina pectoris: chest pain due to reduced cardiac blood flow.
• Myocardial infarction: heart attack occurring with excess hormone levels.
• Severe hyperthyroidism: symptoms such as high fever, severe tachycardia.
• Bone loss: accelerated osteoporosis with long‑term overtreatment.
• Anaphylaxis: rare severe allergic reaction requiring immediate medical attention.

• When prescribing levothyroxine, clinicians should consider several precautionary measures to ensure safe and effective therapy.
• Dose adjustment: monitor TSH and free T4 levels regularly to titrate the dose.
• Cardiovascular disease: use caution in patients with coronary artery disease or arrhythmias.
• Pregnancy: evaluate risks and benefits; dosage may need adjustment under medical supervision.
• Elderly patients: start with lower doses and increase slowly to avoid overtreatment.
• 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 concomitant medicines.

Major Interactions (Avoid)

• Calcium supplements: reduce levothyroxine absorption when taken together.
• Iron salts: markedly decrease levothyroxine bioavailability.
• Antacids containing aluminum or magnesium: interfere with levothyroxine uptake.
• Anticonvulsants (phenytoin, carbamazepine): increase hormone metabolism leading to reduced effect.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect, requiring INR monitoring.
• Estrogen therapy: may increase levothyroxine requirement.
• Cholestyramine: binds levothyroxine in the gut, lowering its absorption.