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Thyroid Hormone Pregnancy: A — safe in pregnancy

Levothyroxine

Brand names: Eltroxin, Euthyrox, Synthroid

Adult dose

Dose: 25–200 micrograms once daily
Route: Oral
Frequency: Once daily on empty stomach, 30min before breakfast
Start 25–50 mcg OD in elderly or cardiac disease. Healthy adults: start 50–100 mcg. Titrate by 25 mcg every 4–6 weeks.

Clinical pearls

  • Take 30–60 min before breakfast fasting — or consistently 1h after breakfast for adherent patients
  • Target TSH 0.4–2.5 mU/L for most patients
  • Start low in elderly, IHD, adrenal insufficiency — avoid rapid correction
  • During pregnancy: increase dose by ~25–30% from confirmed pregnancy (thyroid demand increases)
  • Never switch brands without monitoring — bioavailability varies slightly between preparations

Contraindications

  • Untreated adrenal insufficiency (can precipitate adrenal crisis)
  • Thyrotoxicosis

Side effects

  • Angina, arrhythmias (if dose too high)
  • Tremor
  • Palpitations
  • Insomnia
  • Osteoporosis (long-term over-replacement)

Interactions

  • Calcium, iron, antacids — reduce absorption (separate by 4h)
  • Warfarin — potentiates anticoagulant effect
  • Sertraline, carbamazepine — increase LT4 clearance

Monitoring

  • TSH (6 weeks after dose change, then annually)
  • Free T4 (if TSH abnormal)
  • Bone density (long-term suppressive therapy)

Reference: BTA/BAET Guidelines 2019; ATA Hypothyroidism Guidelines 2014. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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