Letter

Levothyroxine sodium, the active ingredient in Letter, is a thyroid hormone presented as a tablet for oral use. It treats hypothyroidism by replacing deficient thyroid hormone in patients with an underactive thyroid.

GNH USA supplies Letter as a licensed, GDP-compliant international pharmaceutical supplier serving hospitals, pharmacies and clinics worldwide.

Levothyroxine sodium is used in thyroid hormone replacement therapy to manage conditions caused by insufficient endogenous hormone.

- Hypothyroidism: restores normal metabolic activity by providing exogenous thyroxine (T4). - Post‑thyroidectomy hormone replacement: maintains euthyroid status after surgical removal of the thyroid gland. - Congenital hypothyroidism: supplies necessary thyroid hormone to infants born with thyroid deficiency.

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. - Palpitations: sensation 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: - Cardiac arrhythmia: irregular heart rhythm that may be life‑threatening. - Angina pectoris: chest pain due to reduced coronary blood flow. - Myocardial infarction: heart attack in susceptible individuals. - Bone loss/osteoporosis: decreased bone mineral density with long‑term overtreatment. - Severe allergic reaction: rash, swelling, or anaphylaxis. - Adrenal crisis: precipitated in patients with adrenal insufficiency.

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

- Dose titration: adjust based on thyroid function tests and clinical response. - Cardiovascular disease: use cautiously in patients with angina, arrhythmias, or recent myocardial infarction. - Pregnancy and lactation: consult a healthcare professional; dose may need adjustment. - Elderly patients: start with lower doses and monitor for cardiac effects. - Drug interactions: review concomitant medications that may affect absorption or metabolism. - Store at ambient temperature: keep below 25°C, retain in original container, protect from moisture and direct sunlight.

Levothyroxine sodium can have significant interactions that affect its absorption or hormonal activity.

Major Interactions (Avoid): - Calcium supplements: reduce levothyroxine absorption. - Iron salts: markedly decrease oral bioavailability. - Sucralfate: binds and impairs absorption. - Cholestyramine or other bile‑acid sequestrants: lower systemic exposure. - Antacids containing aluminum or magnesium: interfere with uptake.

Moderate Interactions (Monitor Closely): - Warfarin: may enhance anticoagulant effect, requiring INR monitoring. - Diabetes medications: thyroid hormone changes can affect glucose control. - Antidepressants (SSRIs, tricyclics): may alter thyroid hormone levels. - Estrogen therapy: can increase levothyroxine requirement. - Statins: potential modest effect on thyroid hormone metabolism.