standard of care
Synthetic thyroxine (T4). The standard of care for hypothyroidism due to its long half-life (~7 days) and conversion to T3 peripherally, mimicking normal physiology.
- Mechanism: Synthetic T4. Converted to T3 (active form) by deiodinases in peripheral tissues.
- Dosing:
- Full Replacement: (lean body weight). Elderly/Cardiac: Start low () and titrate. Pregnancy: Increase dose by 20–30% immediately upon confirmation.
- PK: Absorption: ~70–80% (reduced by food/calcium/iron). Half-life: 7 days.
indications
- Hypothyroidism: Primary, Central, or Post-surgical.
- TSH Suppression: In differentiated thyroid cancer (target TSH depends on risk).
- Myxoedema Coma: IV loading dose required.
administration advice
- Empty Stomach: Take with water 60 mins before breakfast or 4 hours after last meal.
- Interactions: Separate from Calcium, Iron, PPIs, Bile Acid Sequestrants by 4 hours.
- Monitoring: Check TSH every 4–6 weeks after dose change. Target TSH 0.5–4.0 mIU/L (general population).
cautions
- Overtreatment: Risks atrial fibrillation and osteoporosis (post-menopausal women).
- Bioequivalence: Switching brands can alter TSH; re-check labs 6 weeks after any formulation change.
related pages: Hypothyroidism, Myxoedema Coma