Endocrinology · Synthetic T4
Levothyroxine
Dose
1.6 mcg/kg/d OD; start 25 mcg in elderly / IHD, 50–100 mcg in young
Mechanism
Replaces thyroid hormone
Indications
- • Hypothyroidism (primary, secondary)
- • Thyroid cancer suppression
Use
Take 30–60 min before food; separate from iron, calcium, PPI by 4 h.
Monitoring
TSH at 6–8 weeks then yearly; target 0.5–2.5 in pregnancy.
Side effects
- • Over-replacement: AF, osteoporosis, anxiety
- • Angina exacerbation in IHD
Pregnancy safety
Safe — increase dose ~30% on confirmation
Always confirm dose against your local formulary / BNF before prescribing.
