Levothyroxinnatrium "serb" (Levothyroxine Sodium)

• Levothyroxine sodium is employed to correct deficiencies in thyroid hormone production across several clinical scenarios.
• Hypothyroidism: restores normal thyroid hormone levels, normalising basal metabolic rate and alleviating symptoms such as fatigue, weight gain and cold intolerance.
• Goiter: reduces thyroid‑stimulating hormone stimulation, helping to shrink an enlarged thyroid gland and prevent further growth.
• Post‑thyroidectomy hormone replacement: supplies the necessary thyroxine to maintain metabolic homeostasis after total or near‑total removal of the thyroid gland.

• Levothyroxine sodium is a synthetic analogue of the endogenous hormone thyroxine (T4). After administration it is converted in peripheral tissues to the active hormone triiodothyronine (T3), which binds nuclear thyroid hormone receptors and modulates gene transcription, thereby increasing basal metabolic rate, protein synthesis and normal growth and development.

Levothyroxine sodium may cause a range of adverse reactions, most of which are dose‑related.

Common Side Effects

• Headache: mild to moderate discomfort often occurring shortly after injection.
• Insomnia: difficulty falling or staying asleep, especially at higher doses.
• Palpitations: sensation of rapid or irregular heartbeat.
• Heat intolerance: increased sensitivity to warm environments.

Serious or Rare Side Effects

• Cardiac arrhythmia: abnormal heart rhythm that may require medical attention.
• Angina or myocardial infarction: chest pain or heart attack in susceptible individuals.
• Severe allergic reaction (anaphylaxis): rapid onset of swelling, rash, breathing difficulty.
• Osteoporosis with long‑term overtreatment: decreased bone density increasing fracture risk.
• Adrenal insufficiency exacerbation: worsening of cortisol deficiency symptoms.

• Levothyroxine therapy requires careful monitoring and patient‑specific considerations.
• Dose adjustment: monitor thyroid function tests regularly and titrate to target TSH levels.
• Cardiovascular disease: use caution in patients with coronary artery disease or recent myocardial infarction.
• Pregnancy and lactation: assess risk‑benefit; levothyroxine is preferred for hypothyroidism but data are limited.
• Drug interactions: review concomitant medications that may affect levothyroxine absorption or metabolism.
• Renal impairment: consider dose reduction and close monitoring of thyroid status.
• Store at room temperature: keep below 25 °C in the original container, protect from moisture and light.

Levothyroxine sodium can interact with several medications, altering its efficacy or safety.

Major Interactions (Avoid)

• Calcium supplements: bind levothyroxine in the gut, reducing absorption.
• Iron salts: significantly decrease oral bioavailability of levothyroxine.
• Cholestyramine: sequesters levothyroxine, leading to subtherapeutic levels.
• Sucralfate: forms complexes that impair levothyroxine uptake.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect, requiring INR monitoring.
• Antiepileptic drugs (phenytoin, carbamazepine): increase hepatic metabolism, lowering levothyroxine concentrations.
• Beta‑blockers: may blunt heart‑rate response to levothyroxine, necessitating cardiovascular monitoring.
• Rifampin: induces hepatic enzymes, potentially reducing levothyroxine efficacy.