L-Thyroxin Beta (Levothyroxine Sodium)

Levothyroxine Sodium (L‑Thyroxin Beta) is a thyroid hormone replacement used to treat conditions related to deficient thyroid function.

• Hypothyroidism: restores normal thyroid hormone levels, improving metabolic rate and alleviating symptoms such as fatigue and weight gain.
• Post‑thyroidectomy hormone replacement: provides the necessary hormone after surgical removal of the thyroid gland to maintain normal physiology.
• Congenital hypothyroidism: ensures adequate hormone supply in infants to support growth and neurodevelopment.

• Levothyroxine Sodium is a synthetic form of the endogenous hormone T4. After oral absorption, it binds to nuclear thyroid hormone receptors in target cells, modulating gene transcription that regulates basal metabolic rate, protein synthesis, and growth. By supplying exogenous T4, it compensates for insufficient endogenous production, thereby normalising systemic metabolic activity.

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

Common Side Effects

• Headache: mild to moderate intensity.
• Insomnia: difficulty falling or staying asleep.
• Nervousness or anxiety: heightened nervous system activity.
• Palpitations: awareness of heartbeats.
• Weight loss: unintended reduction in body weight.
• Heat intolerance: increased sensitivity to warm environments.

Serious or Rare Side Effects

• Cardiac arrhythmias: irregular heart rhythm, especially in patients with pre‑existing heart disease.
• Angina or myocardial infarction: chest pain or heart attack due to increased cardiac workload.
• Osteoporosis: reduced bone mineral density with long‑term high dosing.
• Severe allergic reaction: rash, swelling, or anaphylaxis.
• Adrenal insufficiency exacerbation: precipitates adrenal crisis if untreated.

Before initiating therapy, consider the following safety measures.

• Dose adjustment: titrate based on serum TSH and free T4 levels.
• Cardiovascular disease: monitor for tachycardia, angina, or arrhythmias.
• Pregnancy: use only when the benefit outweighs potential risk to the fetus.
• Elderly patients: start with a lower dose and increase cautiously.
• Concomitant medications: review all drugs for potential interactions that may affect absorption or efficacy.
• Store at room temperature: keep in the original container, protect from moisture and light.

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

Major Interactions (Avoid)

• Amiodarone: may increase thyroid hormone levels and risk of hyperthyroidism.
• Warfarin: levothyroxine can enhance anticoagulant effect, requiring INR monitoring.
• Antacids containing aluminum or magnesium: reduce levothyroxine absorption.

Moderate Interactions (Monitor Closely)

• Calcium supplements, iron salts, sucralfate: decrease absorption; separate dosing by at least 4 hours.
• Beta‑blockers: may mask symptoms of excess thyroid hormone.
• Selective serotonin reuptake inhibitors (SSRIs): may alter thyroid hormone metabolism.