Thyroid hormone (T4)

Levothyroxine sodium

Brand names: Eltroxin, various generics

Adult dose

Dose: Initial 50–100 micrograms OD (25 micrograms in elderly/IHD); adjust by 25–50 micrograms every 4–6 weeks per TSH

Route: Oral

Frequency: OD (30–60 min before food)

Clinical pearls

NICE NG145 (Thyroid disease): titrate to TSH 0.4–4.0 mU/L (lower target in selected groups)
BTA (British Thyroid Association) guidance
MHRA safety advice: brand consistency where patient symptomatic on switching
Take consistently — same time daily, away from food/supplements

Contraindications

Untreated thyrotoxicosis
Untreated adrenal insufficiency (treat hydrocortisone first)
Acute MI

Side effects

Symptoms of over-replacement (palpitations, tremor, weight loss, anxiety)
Atrial fibrillation
Osteoporosis (long-term over-replacement)
Allergy to excipients (rare)

Interactions

Iron, calcium, antacids, PPIs (reduced absorption — separate by 4 hours)
Cholestyramine
Enzyme inducers (require dose increase)
Warfarin (potentiation when thyroid status changes)
Oral oestrogens (increase TBG → may need dose increase)

Monitoring

TSH 4–6 weeks post-dose change, then annually when stable
Free T4 if pituitary disease or TSH unreliable

Reference: BNF; NICE NG145; British Thyroid Association; MHRA Drug Safety Update; https://bnf.nice.org.uk/drugs/levothyroxine-sodium/. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways