Levothyroxine Nycomed (Levothyroxine)

Levothyroxine acts on the thyroid hormone pathway to restore normal metabolic function.

• Hypothyroidism: normalizes thyroid hormone levels and alleviates symptoms such as fatigue and weight gain.
• Post‑thyroidectomy replacement: provides necessary thyroxine after surgical removal of the thyroid gland.
• Thyroid cancer suppression: maintains low TSH levels to reduce stimulation of residual thyroid tissue.

• Levothyroxine is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it is converted to the active hormone triiodothyronine (T3) in peripheral tissues, binding to nuclear thyroid hormone receptors and regulating gene transcription that controls basal metabolic rate, protein synthesis, and growth.

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

Common Side Effects

• Headache: mild to moderate discomfort.
• Insomnia: difficulty falling or staying asleep.
• Palpitations: awareness of rapid or irregular heartbeat.
• Weight loss: unintended reduction in body weight.
• Heat intolerance: increased sensitivity to warm environments.
• Tremor: fine shaking of hands or limbs.

Serious or Rare Side Effects

• Allergic reaction: rash, itching, swelling, or anaphylaxis.
• Chest pain: possible indication of cardiac strain.
• Arrhythmia: abnormal heart rhythm requiring medical attention.
• Severe tachycardia: markedly elevated heart rate.
• Bone loss: accelerated osteoporosis with long‑term overtreatment.
• Angina: chest discomfort due to reduced coronary blood flow.

When prescribing Levothyroxine, clinicians should consider several safety measures.

• Dose adjustment in elderly: start with lower doses and titrate slowly.
• Monitor thyroid function: regular TSH and free T4 testing to avoid over‑ or under‑replacement.
• Avoid in untreated adrenal insufficiency: ensure adrenal status is stabilized before therapy.
• Caution in cardiovascular disease: assess risk of angina or arrhythmia.
• Pregnancy and lactation: use only if clearly needed, as safety data are limited.
• Store at ambient temperature: keep below 25°C in the original container, protect from moisture and light.

Levothyroxine can interact with several medicines, affecting its absorption or therapeutic effect.

Major Interactions (Avoid)

• Antacids containing aluminum or magnesium: reduce levothyroxine absorption.
• Calcium supplements: bind to the drug and lower bioavailability.
• Iron salts: interfere with intestinal uptake.
• Warfarin: may enhance anticoagulant effect, requiring INR monitoring.
• Other thyroid hormones: additive effect can cause overtreatment.

Moderate Interactions (Monitor Closely)

• Statins: possible alteration of lipid‑lowering response.
• Beta‑blockers: may mask symptoms of thyrotoxicosis.
• Estrogen therapy: may increase levothyroxine dose requirement.
• Certain antidepressants (e.g., sertraline): may affect thyroid hormone levels.
• Digoxin: altered cardiac effects in hyperthyroid states.