Thyronorm (Levothyroxine) — Indications & Use

Indications (When to Give)

• Hashimoto's thyroiditis (most common)
• Post-thyroidectomy or post-radioiodine therapy
• Drug-induced hypothyroidism (when the offending drug cannot be stopped — e.g., amiodarone, lithium, interferon)
• Congenital hypothyroidism (cretinism) — must treat early to prevent irreversible mental retardation
• Pituitary/hypothalamic disease causing secondary hypothyroidism
• Dyshormonogenesis

• TSH elevated, free T4 normal
• Treat if TSH > 10 mIU/L
• Treat if TSH 4.5–10 with goiter, symptoms, or positive TPO antibodies
• Especially in patients trying to conceive or already pregnant

• All pregnant patients with elevated TSH should receive levothyroxine
• Levothyroxine dose typically needs to increase by 25–30% in pregnancy (iodine demand rises)
• Subclinical hypothyroidism in pregnancy should be treated to ensure healthy fetal outcomes

• Severe, life-threatening hypothyroidism
• IV levothyroxine is used (oral absorption unreliable due to decreased gut motility)
• Initial dose: 200–400 mcg IV bolus, then maintenance doses

• Differentiated thyroid cancer (papillary/follicular): keep TSH suppressed to reduce risk of recurrence
• Some cases of goiter: to reduce thyroid size
• Thyroid nodules: occasionally used (though benefit is debated)

• Detected on neonatal screening (elevated TSH)
• Treatment must begin immediately to prevent irreversible neurodevelopmental damage

Dosing Principles

• Goal: Normalize TSH (0.5–4.5 mIU/L) for most patients
• In thyroid cancer suppression: maintain TSH < 0.1 mIU/L
• Take on empty stomach, 30–60 minutes before breakfast for best absorption

Important Drug Interactions

• Calcium carbonate, antacids, iron supplements: reduce levothyroxine absorption — take 4 hours apart
• Cholestyramine, sucralfate: impair absorption
• Rifampicin, carbamazepine, phenytoin: increase T4 metabolism → may need higher doses
• Warfarin: levothyroxine potentiates anticoagulant effect
• Statins (e.g., pravastatin): co-administration is generally safe but monitor

When NOT to Give (Cautions)

• Untreated adrenal insufficiency: replace corticosteroids first — thyronorm alone can precipitate adrenal crisis
• Acute MI / unstable cardiac disease: use with extreme caution, start low
• Thyrotoxicosis: contraindicated