Thyroid and Anti-thyroid Drugs Flashcards
What thyroid hormone is formed in greater amounts?
T4 (90%)
What are the 3 main proteins that transport T4?
- Transthyretin
- Thyroid Binding Globulin
- Albumin
What enzyme converts T4 to T3?
5’-deiodinase
What is the effect of thyroid hormone on GH?
Increases GH
What is the function of thyroid hormone on uncoupling protein?
Increases it - generates heat
What is the effect of thyroid hormone on the beta-adrenergic receptors?
It will increase their number in the heart
What is the treatment for hypothyroidism?
T3 or T4
Levothyroxine
Mainly T4 so it is less potent and also safer but takes several weeks for action
What is the effect of T4 on warfarin?
Increases the effects of warfarin from protein displacement
What are the treatments for hyperthyroidism?
- Surgery or radiation
- Thioureylenes
- beta-blockers
- Corticosteroids
- Iodide
Thioureylenes (Methimazole/Propylthiouracil)
Inhibit iodide organification via iodination and coupling
What is a unique action of PTU peripherally?
Inhibits peripheral conversion of T4 into T3
What is the more potent thioureylene?
Methimazole
What is the DOC for hyperthyroid pregnant women?
PTU
What are the main SE of PTU and methimazole?
- Agranulocytosis
- Granulocytopenia
- Rash
- Hypothyroidism
Iodide
At high doses it inhibits iodide uptake in the thyroid
What is iodide particularly useful for treating?
Thyroid Storm
Radioactive Iodide MOA
Iodide is taken up and concentrated in the thyroid and the radiation leads to destruction of the gland to reduce activity
Radioactive Iodide SE
Delayed hypothyroidism
Beta Blockers
Blocks the beta receptors on the heart and decreases conversion of T3 to T4
Anion Inhibitors (ClO4-, SCN)
Used only for diagnostic tools as they are highly toxic - compete with iodide uptake
Thyroid Storm
Life threatening situation with large amounts of thyroid hormone - heat intolerance, sweating, tachycardia, etc.
What is the treatment for thyroid storm?
- Acetaminophen - anti-fever
- beta-blockers
- PTU
Levothyroxine MOA
T4 analog converted into T3 which acts as an agonist of VDR
Levothyroxine Indications
Hypothyroidism
Levothyroxine SE
- Hyperthyroidism with overdose
- Risk of atrial fibrillation
- Bone loss in postemenopausal women
Liothyronine MOA
T3 analog and is active hormone that acts as an agonist of the VDR transcription factor
Liothyronine Indications
Hypothyroidism when rapid onset of action is required - myxedema coma or radio iodine therapy for thyroid cancer
Liothyronine SE
Risk of thyrotoxicosis with over dose
What is a physiological example where TBG is increased and what is the response?
Pregnancy will have increased estrogen with increases TBG and leads to decreased T4 that is free reducing the effects of thyroid hormone.
What is the DOC is almost all cases of hypothyroidism?
Levothyroxine
Myxedema Coma
Decreased mental status, hypothermia, hypotension, bradycardia, hypoglycemia and hypoventilation - often precipitated by an acute stressor
Propanolol MOA in Hyperthyroidism
- Ameliorate adrenergic symptoms
- Inhibits the deiodinase enzyme that converts T4 into T3 (small effect/slow onset)
Thioureylenes MOA
- Inhibit Thyroid Peroxidase organification coupling
- PTU partially inibits peripheral deiodination of T4 to T3
Thioureylenes SE
- Skin Reactions – pruritus, rash and urticaria
- Joint Pain‐ arthralgias and arthritis
- Fever
- ANCA
- Hepatotoxicity
Wolf-Chaikoff Effect
‐ negative feedback mechanism
‐ inhibits organification by inhibiting thyroid peroxidase
How can cholestyramine be used in thyroid storm?
Blocks thyroid hormone reabsorption
Amiodarone-induced Thyroid Disease
‐ high iodine content causes Wolff‐Chaikoff effect
‐ inhibits the deiodination of T4 to T3
‐ blocks binding of T3 to Thyroid Hormone Receptor
‐ direct toxic effect on thyroid follicular cells
What is the treatment for thyroid carcinoma?
Complete surgical removal
Thioureylenes (MMI/PTU) MOA
Inhibit Thyroid Peroxidase Organification Coupling
