Levothyroxine Northumbria Pharma (Levothyroxine Sodium)

Levothyroxine is used to treat disorders of thyroid hormone deficiency and related conditions.

• Hypothyroidism: restores normal thyroid hormone levels and alleviates symptoms such as fatigue and weight gain.
• Goiter: reduces thyroid gland enlargement by normalizing hormone feedback.
• Thyroid hormone replacement therapy: provides a stable source of synthetic T4 for patients after thyroidectomy or radioactive iodine treatment.

• Levothyroxine is a synthetic form of the endogenous hormone thyroxine (T4). After oral absorption, it is deiodinated to the active hormone triiodothyronine (T3) in peripheral tissues, binding to nuclear thyroid hormone receptors. This interaction modulates gene transcription, increasing basal metabolic rate and normalizing metabolic processes that depend on thyroid hormone.

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

Common Side Effects

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

Serious or Rare Side Effects

• Cardiac arrhythmias: irregular heart rhythms that may require medical attention.
• Osteoporosis: reduced bone mineral density with long‑term overtreatment.
• Myocardial infarction: rare occurrence in susceptible individuals.
• Severe allergic reaction: rash, swelling, or breathing difficulty.
• Hyperthyroid symptoms: tremor, sweating, or rapid weight loss indicating excess dosing.

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

• Dose titration: adjust based on thyroid function tests and clinical response.
• Cardiovascular disease: use caution in patients with angina, arrhythmias, or recent myocardial infarction.
• Pregnancy and lactation: assess benefits versus risks; dosage may need adjustment.
• Elderly patients: start with lower doses and monitor closely for cardiac effects.
• Drug interactions: review concomitant medications that may alter absorption or metabolism.
• Store at ambient temperature: keep below 25 °C, retain in original container, protect from moisture and light.

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

Major Interactions (Avoid)

• Levothyroxine + Calcium or iron supplements: markedly reduces levothyroxine absorption; separate dosing by at least 4 hours.
• Levothyroxine + Proton pump inhibitors (e.g., omeprazole): may decrease absorption; monitor thyroid levels.
• Levothyroxine + Anticonvulsants (e.g., phenytoin, carbamazepine): increase metabolism leading to reduced efficacy.

Moderate Interactions (Monitor Closely)

• Levothyroxine + Warfarin: may enhance anticoagulant effect; check INR regularly.
• Levothyroxine + Beta‑blockers: may mask tachycardia symptoms of excess hormone.
• Levothyroxine + Cholestyramine: can bind drug and lower its bioavailability.