Thyroid Hormones Flashcards
Drug used to manage hypothyroidism
Levothyroxine
The three primary methods for controlling hyperthyroidism are:
- Antithyroid drug therapy
- Destruction of the gland with radioactive iodine
- Surgical thyroidectomy
THE THIOAMIDES: PROPYLTHIOURACIL & METHIMAZOLE
Propylthiouracil (PTU) and methimazole block thyroid hormone synthesis by inhibiting the peroxidase , thus blocking iodine organification, and coupling of the iodotyrosines.
- PTU also blocks peripheral deiodination of T4 to T3.
- They have no effect on thyroglobulin already stored in the gland. Therefore, clinical effects may be delayed until thyroglobulin stores are depleted.
DOC for Graves’ disease.
Methimazole
• It has a longer half-life, allowing for once-daily dosing, it is efficacious at low doses and has a lower incidence of adverse effects
When is Propylthiouracil (PTU) preferred
in severe hyperthyroid states or thyroid storm.
• PTU is recommended during first trimester of pregnancy due to lesser risk of teratogenic effects.
THE THIOAMIDES: ADVERSE EFFECTS
Pruritic rash
Agranulocytosis
Severe hepatitis (PTU);
IODIDE
- High concentrations of iodide inhibit thyroid hormone release from the gland.
- Iodide is useful in severe thyrotoxicosis and thyroid storm.
- Iodide is used prior to surgery to decrease vascularity of the thyroid gland.
- Adverse effects include sore mouth and throat, swelling of the tongue or larynx, rashes, ulcerations of mucous membranes, and metallic taste.
- Administered orally in solution
- Its therapeutic effect is due to emission of β rays.
- Contraindicated in pregnant or nursing women, since it crosses the placenta to destroy the fetal thyroid gland and it is excreted in breast milk.
RADIOACTIVE IODINE (131I)
treatment of choice for patients with very large glands or multinodular goiters.
- A near-total thyroidectomy
- treated with antithyroid drugs until euthyroid.
- prior to surgery, they receive a saturated solution of potassium iodide, to diminish vascularity of the gland and simplify surgery.
ADJUNCTS TO ANTITHYROID THERAPY
Beta blockers
- reduce tachycardia, tremor, stare, palpitations, and anxiety
- Propranolol at high doses may reduce T3 levels by inhibiting peripheral conversion of T4 to T3.
Calcium channel blockers
- Diltiazem can be used to control tachycardia in
patients in whom β blockers are contraindicated.
THYROID STORM
severe clinical manifestations of thyrotoxicosis
• Precipitating factors include: infections, stress, trauma, thyroidal or nonthyroidal surgery, diabetic ketoacidosis, labor, and heart disease.
THYROID STORM: THERAPEUTIC REGIMEN
Drug that Block iodide uptake
Perchlorate, thiocyanate, nitrate
Block organification of iodine
Thioamides, thiocyanate, sulfonamides
Block coupling reaction
Sulfonamides, thioamides
Block hormone synthesis & release
Lithium, iodide
Block peripheral conversion of T4 to T3
PTU, amiodarone
Increase rate of liver metabolism
Phenobarbital, rifampin, carbamazepine, phenytoin
complications of amiodarone therapy.
Causes both hypo and hyperthyroidism
AMIODARONE-ASSOCIATED HYPOTHYROIDISM (AIH)
A large amount of ingested iodine inhibits thyroid hormone synthesis
Thyroid function can be normalized with
levothyroxine if amiodarone cannot be stopped.
AMIODARONE-ASSOCIATED HYPERTHYROIDISM (AIT)
Type 1
- There is increased synthesis of T4 and T3 due to iodine from amiodarone.
- Occurs in patients with preexisting goiter.
- Treated with high dose methimazole or propylthiouracil.
AMIODARONE-ASSOCIATED HYPERTHYROIDISM (AIT)
Type 2
- Destructive thyroiditis results in excess release of T4 and T3.
- Typically occurs in euthyroid patients.
- Caused by direct toxic effect of amiodarone on thyroid follicular epithelial cells. Treated with glucocorticoids.
