Levothyroxine Aristo (Anhydrous Levothyroxine Sodium)

Levothyroxine is a synthetic thyroid hormone used in the management of disorders that involve deficient thyroid hormone production.

• Hypothyroidism: restores normal thyroid hormone levels, relieving symptoms such as fatigue, weight gain, and cold intolerance.
• Congenital hypothyroidism: provides essential hormone replacement in newborns to support growth and neurodevelopment.
• Post‑thyroidectomy replacement: supplies thyroid hormone after surgical removal of the thyroid gland to maintain metabolic balance.
• Goiter: reduces gland enlargement by normalizing circulating thyroid hormone concentrations.

• Levothyroxine is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it binds to plasma proteins and is taken up by peripheral tissues, where deiodinase enzymes convert it to the active triiodothyronine (T3). The resulting T3 interacts with nuclear thyroid hormone receptors, modulating gene transcription that regulates basal metabolic rate, protein synthesis, and growth. This cascade restores normal metabolic activity throughout the body.

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

Common Side Effects

• Headache: mild to moderate headache may occur during dose titration.
• Insomnia: difficulty sleeping is reported, especially with higher doses.
• 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: potentially life‑threatening irregular heart rhythm.
• Angina pectoris: chest pain due to reduced coronary blood flow.
• Myocardial infarction: rare occurrence of heart attack.
• Osteoporosis: accelerated bone loss with long‑term overtreatment.
• Severe allergic reaction: rash, swelling, or anaphylaxis.
• Hyperthyroidism crisis: symptoms of excessive thyroid activity such as fever and agitation.

Before initiating Levothyroxine therapy, several precautions should be considered to ensure safe and effective use.

• Dose adjustment: monitor thyroid function tests regularly and adjust dose accordingly.
• Cardiovascular disease: use caution in patients with coronary artery disease or arrhythmias.
• Elderly patients: start with a lower dose and titrate slowly.
• Pregnancy: discuss potential risks and benefits with a healthcare professional.
• Drug interactions: review all concomitant medications for possible absorption or metabolic interactions.
• Store at room temperature: keep in the original container, protect from moisture and light.

Levothyroxine interacts with several medicines that can alter its absorption or effect on thyroid function.

Major Interactions (Avoid)

• Calcium supplements: concomitant use reduces levothyroxine absorption, requiring separation of dosing by at least 4 hours.
• Iron salts: simultaneous ingestion decreases levothyroxine bioavailability; advise taking levothyroxine on an empty stomach.
• Antacids containing aluminum or magnesium: impair levothyroxine uptake from the gut; separate administration by several hours.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect, potentially altering INR; monitor clotting parameters closely.
• Amiodarone: can affect thyroid hormone synthesis and metabolism, often necessitating levothyroxine dose adjustments.
• Carbamazepine: may increase metabolic clearance of levothyroxine, lowering its efficacy and requiring dose reassessment.