Medithyrox (Levothyroxine Sodium)

• Medithyrox, a synthetic thyroid hormone, is used to manage conditions where thyroid hormone levels are insufficient.
• Hypothyroidism: restores normal metabolic rate and alleviates symptoms such as fatigue and weight gain.
• Post‑thyroidectomy replacement: provides necessary thyroid hormone after surgical removal of the thyroid gland.
• Goitre: helps normalize thyroid function and reduce gland enlargement.

• Levothyroxine sodium 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. This interaction modulates gene transcription, increasing basal metabolic activity, protein synthesis, and oxygen consumption, thereby compensating for deficient endogenous hormone production. The resulting rise in circulating T4 and T3 levels re‑establishes euthyroid status and normalizes physiological processes.

Levothyroxine therapy may be associated with a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Headache: mild headache reported especially after dose changes.
• Insomnia: difficulty sleeping or altered sleep patterns.
• Palpitations: sensation of rapid or irregular heartbeat.
• Weight loss: unintended loss of weight due to increased metabolism.
• Heat intolerance: excessive sweating and feeling overly warm.
• Nausea: mild gastrointestinal upset.

Serious or Rare Side Effects

• Cardiac arrhythmia: potentially life‑threatening irregular heart rhythm.
• Angina or myocardial infarction: chest pain or heart attack in susceptible patients.
• Severe allergic reaction: rash, swelling, or anaphylaxis requiring immediate medical attention.
• Bone loss: accelerated osteoporosis with long‑term overtreatment.
• Severe tachycardia: markedly increased heart rate that may require emergency care.
• Myocardial ischemia: reduced blood flow to the heart muscle in high‑risk individuals.

When prescribing Levothyroxine sodium, clinicians should consider several precautionary measures to ensure safe and effective therapy.

• Dose adjustment in elderly: start with lower dose and titrate cautiously.
• Monitor thyroid function tests: check TSH and free T4 regularly after initiation or dose changes.
• Avoid use in untreated adrenal insufficiency: ensure cortisol replacement before starting therapy.
• Caution in cardiovascular disease: patients with angina or arrhythmias may require careful monitoring.
• Pregnancy and lactation: assess risk‑benefit, as dosing may need adjustment.
• Store at ambient temperature: keep tablets below 25 °C in original packaging, protected from moisture.

Levothyroxine sodium can interact with various medicines, affecting its absorption or hormonal activity.

Major Interactions (Avoid)

• Antacids containing aluminum or magnesium: significantly reduce levothyroxine absorption.
• Calcium supplements: bind levothyroxine and lower its bioavailability.
• Iron preparations: decrease absorption when taken concurrently.
• Cholestyramine or other bile‑acid sequestrants: impair levothyroxine uptake.
• Sucralfate: forms complexes that diminish absorption.

Moderate Interactions (Monitor Closely)

• Warfarin: levothyroxine may enhance anticoagulant effect, requiring INR monitoring.
• Amiodarone: can alter thyroid hormone levels, necessitating dose adjustments.
• Oral contraceptives: may increase levothyroxine requirement.
• Diabetes medications: thyroid hormone changes can affect glucose control.
• Serotonergic agents: monitor for potential mood changes.