Thyrotab

Approved Indications:

• Primary, Secondary, and Tertiary Hypothyroidism (congenital or acquired)
• Euthyroid Goiter: Including nodular goiter, Hashimoto’s thyroiditis, and iodine deficiency-related goiter
• Thyroid Cancer: As adjunct therapy to suppress TSH in thyrotropin-dependent, well-differentiated thyroid cancer
• Myxedema Coma: As an emergency treatment (IV route)
• Thyroid Suppression Test: For thyroid function evaluation

Clinically Accepted Off-Label Uses:

• Subclinical Hypothyroidism: Especially in pregnancy, infertility, or goiter
• Depression Augmentation: As adjunct in treatment-resistant depression (specialist-supervised)
• Post-Thyroidectomy Replacement Therapy: In patients with total thyroidectomy

Adults (Oral):

• Initial dose (healthy <50 years): 1.6 mcg/kg/day
• Elderly or cardiac disease: Start at 12.5–25 mcg/day; titrate every 6–8 weeks
• Usual maintenance dose: 100–125 mcg/day

Pediatrics (Oral):

• Neonates: 10–15 mcg/kg/day
• Infants 6 months–1 year: 6–8 mcg/kg/day
• Children 1–5 years: 5–6 mcg/kg/day
• Children 6–12 years: 4–5 mcg/kg/day
• Adolescents: 2–3 mcg/kg/day

Myxedema Coma (IV):

• Initial dose: 200–400 mcg IV bolus
• Maintenance: 50–100 mcg IV daily

Special Populations:

• Pregnancy: Increase dose by ~30–50%; monitor TSH every 4–6 weeks
• Elderly: Start low and titrate slowly
• Renal/Hepatic Impairment: No initial adjustment, but monitor TSH closely

Administration Tips:

• Take on an empty stomach, 30–60 minutes before breakfast
• Avoid calcium, iron, soy, and antacids within 4 hours

Levothyroxine is a synthetic T4 hormone that mimics the action of natural thyroxine. In peripheral tissues, it is converted to triiodothyronine (T3), which binds nuclear thyroid hormone receptors. This interaction regulates gene transcription and protein synthesis, essential for metabolic homeostasis, growth, development, and thermoregulation. The net effect restores normal metabolism in hypothyroid patients.

• Absorption: 40–80%; decreased by food and certain drugs
• Peak Plasma Time: 2–4 hours (oral)
• Distribution: >99% protein-bound (TBG, albumin, transthyretin)
• Metabolism: Hepatic and renal deiodination to T3 and reverse T3
• Half-life: ~7 days (normal), shorter in hyperthyroidism, longer in hypothyroidism
• Excretion: Renal (~80%), fecal (~20%)

• Pregnancy: Category A. Safe and essential. Dose adjustment required due to increased thyroxine-binding globulin.
• Lactation: Minimal transfer into breast milk. Considered safe. No adverse effects reported in nursing infants.

• Primary Class: Thyroid Hormone Replacement
• Subclass: Synthetic T4 analog

• Known hypersensitivity to levothyroxine or its excipients
• Untreated thyrotoxicosis
• Uncorrected adrenal insufficiency
• Acute myocardial infarction (caution during initiation)

• Cardiovascular Risk: Overdosing may cause arrhythmia or angina in susceptible patients
• Bone Loss: Long-term overuse may lead to osteoporosis, especially in postmenopausal women
• Adrenal Function: Evaluate for adrenal insufficiency before initiation
• Monitoring: TSH every 6–8 weeks after any dose adjustment
• Not for Weight Loss: Use in euthyroid individuals can be life-threatening

Common (mostly from overdosage):

• Palpitations, tachycardia
• Nervousness, anxiety
• Insomnia
• Heat intolerance
• Weight loss

Rare/Serious:

• Atrial fibrillation
• Chest pain, myocardial ischemia
• Pseudotumor cerebri (in children)
• Seizures (rare)
• Allergic skin reactions

Reduced Absorption:

• Iron, calcium, antacids, cholestyramine, sucralfate

Enzyme Inducers:

• Rifampin, carbamazepine, phenytoin (↑ clearance)

Enhanced Effects:

• Warfarin (↑ anticoagulant activity)

Other:

• Estrogens ↑ TBG levels, requiring higher dose
• Antidiabetics may have reduced efficacy

• ATA Guidelines (2023): Stress individualized dosing and tighter monitoring during pregnancy and in elderly
• Pregnancy Dosing: Increase immediately upon confirmation of pregnancy
• Avoid T4+T3 Combinations: T4 monotherapy remains first-line

• Temperature: Store at 20°C to 25°C (68°F to 77°F)
• Permitted Excursions: 15°C to 30°C
• Humidity/Light: Protect from moisture and light; store in original container
• Handling: Do not refrigerate; avoid transferring tablets to pill organizers for long periods