L-Тироксин (Levothyroxine Sodium)

L‑Тироксин is a synthetic thyroid hormone used to treat conditions that require hormone replacement or regulation.

• Hypothyroidism: restores normal metabolic rate and alleviates symptoms of low thyroid function.
• Post‑thyroidectomy replacement: provides necessary thyroxine after surgical removal of the thyroid gland.
• Goiter: reduces gland enlargement by normalising circulating thyroid hormone levels.
• Congenital hypothyroidism: ensures adequate hormone supply for growth and development in newborns.

• Levothyroxine Sodium is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it circulates in the bloodstream and enters cells, where deiodinase enzymes convert it to the active triiodothyronine (T3). Both T4 and T3 bind to nuclear thyroid hormone receptors, modulating gene transcription that regulates basal metabolic rate, protein synthesis, and growth across multiple organ systems.

Adverse reactions may occur with levothyroxine therapy. Patients should be aware of both common and less frequent events.

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.
• Diarrhea: loose stools or increased bowel movements.

Serious or Rare Side Effects

• Cardiac arrhythmias: potentially life‑threatening rhythm disturbances.
• Angina or chest pain: signs of myocardial ischemia.
• Osteoporosis: decreased bone mineral density with long‑term excess.
• Hyperthyroid symptoms: tremor, heat intolerance, sweating.
• Allergic reactions: rash, pruritus, or angioedema.
• Severe muscle weakness: rare myopathy.

Before initiating therapy, consider the following safety measures.

• Assess thyroid function: confirm diagnosis with serum TSH and free T4 levels.
• Monitor cardiovascular status: caution in patients with coronary artery disease.
• Adjust dose in the elderly: start with lower doses to avoid overtreatment.
• Review concomitant medications: some drugs alter levothyroxine absorption.
• Pregnancy and lactation: evaluate risk‑benefit under medical supervision.
• Store below 25°C: keep in the original container, protect from moisture and direct light.

Levothyroxine may interact with several medicines, affecting its efficacy or safety.

Major Interactions (Avoid)

• Levothyroxine + warfarin: increased anticoagulant effect, monitor INR closely.
• Levothyroxine + insulin or oral hypoglycemics: enhanced hypoglycaemic response.
• Levothyroxine + amiodarone: may exacerbate thyroid dysfunction.

Moderate Interactions (Monitor Closely)

• Levothyroxine + calcium or iron supplements: reduced absorption, separate dosing by at least 4 hours.
• Levothyroxine + proton‑pump inhibitors or H2 blockers: may decrease bioavailability.
• Levothyroxine + cholesterol‑lowering agents (e.g., cholestyramine): possible reduction in hormone levels.