Levothyroxine Serb (Levothyroxine Sodium)

Levothyroxine is a thyroid hormone replacement that addresses disorders of thyroid hormone deficiency.

• Hypothyroidism: restores normal thyroid hormone levels, improving metabolic function and alleviating symptoms such as fatigue and weight gain.
• Thyroid hormone replacement: provides exogenous T4 for patients after thyroidectomy or radioactive iodine therapy, maintaining euthyroid status.
• Goiter: reduces thyroid‑stimulating hormone drive, helping to shrink an enlarged thyroid gland.

• Levothyroxine is a synthetic form of the endogenous hormone thyroxine (T4). After administration, it is absorbed and converted to the active hormone triiodothyronine (T3) in peripheral tissues. The hormone binds nuclear thyroid hormone receptors, modulating gene transcription that regulates basal metabolic rate, protein synthesis, and sympathetic nervous system activity, thereby normalizing metabolic processes that are deficient in hypothyroid states.

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

Common Side Effects

• Headache: mild to moderate pain in the head region.
• Insomnia: difficulty initiating or maintaining sleep.
• Palpitations: awareness of rapid or irregular heartbeat.
• Heat intolerance: increased sensitivity to warm environments.
• Tremor: fine shaking of the hands or limbs.
• Anxiety: feelings of nervousness or unease.

Serious or Rare Side Effects

• Cardiac arrhythmia: abnormal heart rhythm that may be life‑threatening.
• Angina pectoris: chest pain due to myocardial ischemia.
• Myocardial infarction: heart attack resulting from coronary artery blockage.
• Severe allergic reaction: rash, swelling, or anaphylaxis requiring immediate care.
• Osteoporosis: loss of bone density with prolonged overtreatment.
• Hyperthyroidism symptoms: excessive sweating, weight loss, and tremor indicating overtreatment.

When using Levothyroxine, several safety considerations should be observed to minimize risks.

• Dose titration in elderly: start with lower doses and adjust gradually to avoid cardiac stress.
• Monitor thyroid function: regularly check TSH and free T4 levels to maintain target range.
• Avoid in untreated adrenal insufficiency: ensure adrenal function is adequate before initiating therapy.
• Caution in cardiovascular disease: patients with angina or arrhythmias require careful monitoring.
• Pregnancy and lactation: use only if benefits outweigh risks and under medical supervision.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Levothyroxine interacts with several medicines that can alter its absorption or pharmacodynamic effect.

Major Interactions (Avoid)

• Calcium supplements: reduce levothyroxine absorption; separate dosing by at least 4 hours.
• Iron salts: markedly decrease absorption; administer at different times.
• Sucralfate: binds levothyroxine in the gut, diminishing its effectiveness.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect; monitor INR.
• Oral contraceptives: may increase levothyroxine requirement; check thyroid function.