What is the organification step the biosynthesis of TH?
Adding of Iodine to the tyrosine residues on thyroglobulin
Name the two drugs used in management of hypothyroidism.
Levothyroxine (Isomer of T4)
Liothyronine (isomer of T3)
Which drug is used for myxedema coma?
IV levothyroxine
-this condition is an emergent exacerbation of hypothyroidism and sometimes the faster-acting T3 isomer is needed to reverse the condition so
Liothyronine can also be used but is more difficult to monitor
What are symptoms of myxedema coma?
altered mental status, hypothermia, hypoglycemia, hypotension, hyponatremia, hypercapnia, hypoxia, bradycardia, and hypoventilation
ironically myxedema is not always present
How is myxedema treated?
Begin with low doses
Myxedema is a manifestation of severe hypothyroidism. The treatment is replacement of TH (either Liothyronine or Levothyroxine). However, myxedema is associated with coronary artery disease. Giving TH too quickly will increase metabolism in the body and O2 demand on the heart and exacerbate angina pectoris, cause MI or arrhythmias.
Name the two drugs that induce CYP causing hypothyroidism.
Rifampin, Phenytoin
-induce metabolism of T3 and T4
Antiarrhythmic that causes hypothyroidism and the mechanism.
Amiodarone
- resembles TH and releases lots of iodine into the blood.
- a high amount of iodine is taken up by the thyroid gland inducing an autoregulation mechanism (Wolff-Chaikoff effect)
- the WC effect prevents organification and release of TH
Name the serious cardio, MSK, and neuro side effects of Levothyroxine and Liothyronine.
Cardio: MI
MSK: decreased bone density, hip fracture
Neuro: pseudotumor cerebri, seizure
Name the two drugs used for Hyperthyroidism therapy and the MOA.
Methimazole
Propylthiouracil
MOA: inhibit thyroid peroxidase (TPO)
(Propylthiouracil also inhibits deiodination of T4 to T3)
First line drug for children and adults with hyperthyroidism.
Methimazole
Contraindication of methimazole.
Teratogenic (-azole ending)
- causes fetal scalp defect
- ability to cross placenta because it does not bind plasma proteins
Which 3 clinical settings prefer propylthiouracil to methimazole in treatment of hyperthyroidism?
- Pregnncy
- Life-threatening thyrotoxicosis or thyroid storm
- Patients with adverse rxns to methimazole
Major side effects of the thioamides.
Methimazole: rash, altered sense of smell, agranulocytosis
Propylthiouracil: rash, liver toxicity
In what setting is antithyroid medication preferred for treatment of hyperthyroidism?
Best for children and adults with mild disease
In what setting is surgery the best treatment for hyperthyroidism?
Best for large glands or multinodular goiters
In what setting is radioiodine ablation of the thyroid best.
In patients older than 21
What are the 3 steps in surgical removal of the thyroid gland?
- Treat w/ anti-thyroid meds to until euthyroid state (normal TH hormone levels) is reached
- Administer Potassium Iodide to induce the WC effect and reduce vascularity to the organ
- Perform the surgery
Contraindication to thyroid gland surgery.
Pregnancy
- potassium iodide causes fetal goiter
- other drug options are available but are not very effective
MOA of radioactive iodine
MOA: iodine rapidly absorbed by thyroid cells, emits beta-rays that destroy thyroid parenchyma
Name the two Beta blockers used in hyperthyroidism and why.
Propranolol (preferred)
Esmolol
-both are used to treat symptoms: sweating, tachycardia, tremor
