Thyroid Flashcards
How does iodide get into the thyroid follicles?
Via a sodium-iodide symporter.
Where is the Thyroid Hormone receptor located and what is it composed of?
In the nucleus: retinoic acid receptor and TR monomer.
What is the main physiological effect of Thyroid Hormone?
To increase metabolism/BMR
What is a T4 replacement?
Levothyroxine Sodium
What is a T3 replacement?
Liothyronine Sodium
More rapidly effective and eliminated faster (4x more potent than levothyroxine).
What is a mixture of T4 and T3?
Liotrix
What is the preferred drug for use in the treatment of hypothyroidism?
Levothyroxine Sodium (T4)
Longer half-life than Liothyronine
Who requires a higher dose of levothyroxine? Who requires a lower dose?
Higher: infants/children
Lower: patients with angina pectoris
When do you give IV liothyronine?
In acute emergency conditions.
Which drug is less desirable for chronic replacement therapy?
Liothyronine (less stable, more costly).
TSH levels are usually what in hyperthyroidism?
Decreased
What are the anti-thyroid drugs and how do they work?
Propylthiouracil, Methimazole, Carbimazole
They inhibit the organification of iodide and coupling of iodotryrosine, thus inhibiting thyroid hormone synthesis.
Propylthiouracil also reduces the deiodinization of T4 to T3.
What is the active metabolite of Carbimazole?
Methimazole
When do you give a higher dosage of anti-thyroid drugs?
For thyrotoxicosis.
What are the 3 severe side effects of anti-thyroid drugs?
Agranulocytosis (worse in Propylthiouracil), Hepatitis and Lupus-like syndrome
How does Methimazole compare to Propylthiouracil?
Lower risk of agranulocytosis, higher concentration in breast milk, longer half-life, slower excretion
What is the preferred anti-thyroid drug for pregnancy?
Propylthiouracil: less likely to cross the placenta.
What is the purpose of radioactive iodine?
It destroys sufficient thyroid tissue to restore euthyroid.
When is radioactive iodine used?
Treatment of choice for relapsed hyperthyroidism after antithyroid drug therapy.
Also, larger doses are used after thyroid cancer surgery to destroy any remaining cancer cells.
[Since effects are not seen for over 4 weeks, patients with severe hyperthyroidism should combine antithyroids or a beta-blocker until it takes effect]
What is a side effect of radioactive iodine treatment?
May cause permanent hypothyroidism.
Do not give to pregnant or breast-feeding women. Should not be initial treatment for children (use anti-thyroid drugs).
When are beta-blockers used for hyperthyroidism?
Only when symptoms are moderate or severe. They are used as adjunctive agents in Graves’ to control tremor, anxiety, palpitations, etc.
