Thyroactive Drug
Thyroactive drugs are used to either stimulate or suppress thyroid hormone production and activity. They are essential in the management of hypothyroidism, hyperthyroidism, thyroid cancer, and thyroid storm.
Pharmacodynamics
- Iodine / Potassium Iodide:
- Required for T3 & T4 synthesis.
- Used for iodine deficiency, pre-op prep, and thyroid storm (inhibits hormone release at high doses).
- Levothyroxine (T4):
- Synthetic thyroxine.
- Used in hypothyroidism, TSH suppression (e.g., in thyroid cancer).
- Slower onset but longer action.
- Liothyronine (T3):
- Synthetic triiodothyronine.
- Faster onset, shorter half-life.
- Used in acute hypothyroid states or as adjunct in depression.
- Methimazole:
- Inhibits thyroid peroxidase → prevents hormone synthesis.
- Used in hyperthyroidism, Graves' disease, thyroid storm.
- Propylthiouracil (PTU):
- Inhibits thyroid peroxidase and also T4 → T3 conversion.
- Used in thyroid storm and 1st trimester of pregnancy (less teratogenic than methimazole).
Side Effects
Common:
- GI upset (nausea, vomiting, diarrhea)
- Headache, dizziness
- Sleep disturbances
- Appetite/weight changes
- Hair thinning
- Sweating, heat intolerance
Rare but Serious:
- Agranulocytosis (especially with methimazole and PTU)
- Hepatotoxicity (PTU > methimazole)
- Cardiac arrhythmias
- CNS effects (seizures, confusion)
- Allergic reactions (rash, swelling)