rapid acting thyroid hormone
Synthetic triiodothyronine (T3). Rarely used for routine replacement due to short half-life and “peak” effects, but essential in Myxoedema Coma where peripheral conversion of T4 is impaired.
- Mechanism: Active thyroid hormone (T3). Bypasses the need for peripheral deiodination.
- Dosing: - Myxoedema Coma: 5–20 IV loading dose, then 2.5–10 q8h. - Thyroid Cancer: Short-term withdrawal prep for RAI scan (historical).
- PK: Onset: Rapid (hours). Half-life: ~1 day. Wide fluctuations in serum levels if used as chronic replacement.
indications
- Myxoedema Coma: To rapidly restore intracellular T3, especially in sick patients with “Euthyroid Sick Syndrome” physiology (impaired T4 T3).
- Depression: Augmentation therapy (Psychiatry).
cautions
- Cardiac Toxicity: Rapid peaks can precipitate arrhythmia, angina, or MI in susceptible patients. Use caution in the elderly or those with CAD.
- Monitoring: TSH is still the target, but fT3 levels will fluctuate wildly.
related pages: Levothyroxine, Myxoedema Coma