L-Thyroxin Levothyroxin-Natrium Aventis (Levothyroxine Sodium)

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

• Hypothyroidism: normalises low thyroid hormone levels and alleviates associated symptoms.
• Post‑thyroidectomy hormone replacement: provides the missing thyroid hormone after surgical removal of the gland.
• Goitre: reduces gland enlargement by supplying adequate hormone and suppressing TSH stimulation.

• Levothyroxine Sodium is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it enters the bloodstream and is converted to the active triiodothyronine (T3) within target tissues. The active hormone binds nuclear thyroid hormone receptors, modulating gene transcription that increases basal metabolic rate, influences protein synthesis, and supports growth and development.

Levothyroxine Sodium 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.
• Nervousness or anxiety: heightened nervous system activity.
• Weight loss: unintended reduction in body weight.
• Insomnia: difficulty initiating or maintaining sleep.
• Gastrointestinal upset: nausea, abdominal cramps, or diarrhoea.

Serious or Rare Side Effects

• Cardiac arrhythmias: potentially life‑threatening rhythm disturbances.
• Osteoporosis: decreased bone mineral density with long‑term overtreatment.
• Hyperthyroidism symptoms: tremor, heat intolerance, or excessive sweating.
• Allergic reactions: rash, pruritus, or angio‑edema.
• Myocardial ischaemia: chest pain or angina in susceptible individuals.

Levothyroxine Sodium requires careful monitoring to avoid over‑ or under‑replacement.

• Dose titration: adjust based on thyroid function tests and clinical response.
• Cardiovascular disease: use cautiously in patients with angina, arrhythmias, or recent myocardial infarction.
• Osteoporosis risk: monitor bone health in long‑term high‑dose therapy, especially in postmenopausal women.
• Pregnancy and lactation: evaluate benefits versus risks; dosage may need adjustment.
• Drug interactions: review concomitant medications that may affect absorption or metabolism.

Store at room temperature: keep in the original container, protect from moisture and direct sunlight.

Levothyroxine Sodium can interact with several medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Antacids containing aluminium or magnesium: reduce levothyroxine absorption; separate dosing by at least 4 hours.
• Iron supplements: markedly decrease absorption; separate dosing by at least 4 hours.
• Corticosteroids (e.g., prednisone): may increase thyroid hormone requirements.

Moderate Interactions (Monitor Closely)

• Proton‑pump inhibitors (e.g., omeprazole): may modestly reduce absorption; monitor thyroid levels.
• Cholestyramine or colestipol: bind levothyroxine and lower its bioavailability.
• Selective serotonin reuptake inhibitors (e.g., sertraline): may slightly increase thyroid hormone levels.
• Warfarin: levothyroxine may enhance anticoagulant effect; monitor INR closely.