Synthetic T₄

USE: For chronic hypothyroidism. Longer half-life (6-7 days) than T₃ (Liothyronine). Converted to T₃ in liver and peripheral tissues (except Chronic Fatigue Syndrome can't).

CAUTION: Infants and children need more T₄ than adult dose. Use lower doses initially in patients with angina pectoris.

Synthetic T₃.

USE: Use acutely--reaches peak levels 2-4 hours after oral administration but is eliminated more rapidly. Use IV in ED for myxedema coma. Not recommended for long-term replacement due to expense and instability.

1) Subtotal thyroidectomy + replace T_4.

2) Irradiate thyroid gland + replace T₄.

3) Inhibit thyroid peroxidase activity with antithyroid drugs.

4) Interfere with thyroid hormone facilitation of sympathetic activity (β-blockers--block downstream effects of thyroid hormone).

MECH: 1) Inhibits organification of iodide and coupling of iodotyrosine ----> inhibits thyroid hormone synth. 2) Inhibits the deiodination of T₄ to T₃.

USE: For hyperthyroidism in Pregnants (less transplacental passage, lower concentration in breast milk)

AE: Agranulocytosis (higher risk), hepatitis, lupus-like syndrome.

Active metabolite of Carbimazole (Carbimazole not available in US).

MECH: 1) Inhibits organification of iodide and coupling of iodotyrosine ----> inhibits thyroid hormone synth. 2) Inhibits the deiodination of T₄ to T₃ (but not as much as PTU).

USE: For hyperthyroidism treatment.

AE: Agranulocytosis (lower risk), hepatitis, lupus-like syndrome.

Emits beta-particles and gamma rays with a half-life of 5 days.

Takes effect in 4 weeks (should be used with drug therapy).

USE: Relapsed hyperthyroidism after antithyroid drug therapy. Monitor thyroid hormones after therapy (every 2-3 months in first year, then yearly).

AE: Does NOT increase risk of cancer.

CONTRA: Pregnancy, Breast-feeding, children <10.