Levothyroxine Accord-Uk (Anhydrous Levothyroxine Sodium)

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

• Hypothyroidism: normalizes thyroid hormone levels and alleviates fatigue, weight gain, and cold intolerance.
• Thyroid hormone replacement therapy: provides a stable source of T4 for patients after thyroidectomy or radioactive iodine treatment.
• Goiter: reduces gland size by correcting hormonal deficiency that stimulates thyroid growth.

• 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. This interaction modulates gene transcription, increasing basal metabolic rate, protein synthesis, and oxygen consumption, thereby correcting the metabolic deficit caused by thyroid hormone insufficiency.

Levothyroxine may cause a range of adverse reactions, most of which are dose‑related and reversible upon adjustment.

Common Side Effects

• Headache: mild to moderate discomfort often occurring early in therapy.
• Nervousness: feelings of anxiety or restlessness.
• Insomnia: difficulty falling or staying asleep.
• Weight loss: unintended reduction in body weight.
• Palpitations: sensation of rapid or irregular heartbeat.
• Heat intolerance: increased sensitivity to warm environments.

Serious or Rare Side Effects

• Chest pain: may indicate cardiac strain.
• Severe tachycardia: excessively fast heart rate requiring medical attention.
• Arrhythmia: irregular heart rhythm.
• Bone loss (osteoporosis): long‑term excess hormone exposure.
• Allergic reaction (rash, swelling, breathing difficulty): signs of hypersensitivity.
• Myocardial infarction: rare but possible in susceptible individuals.

Levothyroxine requires careful monitoring and individualized dosing to avoid over‑ or under‑replacement.

• Dose titration: adjust based on serial TSH and free T4 measurements.
• Cardiovascular disease: monitor heart rate and rhythm, especially in patients with coronary artery disease.
• Elderly patients: initiate therapy at lower doses to reduce risk of cardiac events.
• Pregnancy: use only when the expected benefit justifies potential risk to the fetus.
• Drug monitoring: regular thyroid function tests are essential for safe long‑term use.
• Store at ambient temperature: keep in the original container, protect from moisture and light.

Levothyroxine absorption and metabolism can be altered by several concomitant medicines.

Major Interactions (Avoid)

• Calcium supplements: reduce levothyroxine absorption when taken together.
• Iron salts: decrease bioavailability if administered within the same hour.
• Antacids containing aluminum or magnesium: interfere with gastrointestinal uptake.
• Amiodarone: may cause unpredictable changes in thyroid hormone levels.
• Warfarin: levothyroxine can enhance anticoagulant effect, requiring INR monitoring.

Moderate Interactions (Monitor Closely)

• Beta‑blockers: may mask symptoms of hyperthyroidism.
• Corticosteroids: increase hormone metabolism, potentially lowering efficacy.
• Phenobarbital and phenytoin: induce hepatic enzymes, increasing clearance.
• Cholestyramine: binds levothyroxine and reduces absorption.
• Rifampin: decreases serum levothyroxine concentrations, possibly necessitating dose adjustment.