Studied by 3 people
What is the minimum amount of iodine required per day?
150 micograms/day
Where is excess iodine excreted?
urine and stool
What is the Wolff-Chaikoff effect?
high iodine levels can inhibit further iodine uptake into the thyroid → transient hypothyroid symptoms
Where is T4 converted to T3?
in the periphery
Which form of iodine makes up the bulk of iodine in the body?
T4 - 90%
What form of iodine is considered active thyroid hormone?
T3 - 9%
What form of iodine is biologically inactive?
rT3 - 1%
What is the T 1/2 of T4?
7 days
What is the T 1/2 of T3?
1 day
Which form of iodine has a greater oral bioavalabity?
T3 - 95% oral absorption
How much T4 is naturally made by the body per day?
75 mcg
How much T3 is naturally made by the body per day?
25 mcg
What is the major function of TH?
regulate growth & development in fetal & childhood
regulates metabolism
regulates energy expenditure
What is the condition called with iodine deficiency during fetal development?
Cretinism- PREVENTABLE
What is iodine deficiency in adults called?
myxedema
can cause coma
What is hyperthyroidism?
Thyroid hormone in excess
What is hypothyroidism?
thyroid hormone deficiency
What is the TSH level with hypothyroidism?
High TSH → continually saying need more TH
What is the TSH level in hyperthyroidism?
Low TSH
What is Hashimoto’s disease?
Hypothyroidism
destructive autoantibodies attack thyroid gland
High TSH- signal need more TH
What is Grave’s disease?
Hyperthyroidism
stimulatory autoantibody stimulate TH
low TSH level bc excess
What are S/S of Grave’s disease?
skin: sweating, heat intolerance, thinning hair
ocular: upper eyelid retraction - BUG EYES
CV: elevated HR, Increased CO, arrhythmias, angina
Respiratory: Hypoventilation
GI: Increased peristaltic contractions
CNS: agitation, nervousness
Muscle: weakness, fatigue
Reproductive: Menstrual irregularities, infertility
Metabolic: Increased BMR, Increased drug metabolism
What is a thyroid storm?
acute exacerbation of hyperthyroidism - LIFE THREATENING
What are S/s of a thyroid storm?
palpitations
HF
hyperthermia
What is the treatment for a thyroid storm?
CV symptoms- non-selective beta blockers (propranolol) if BB CI then use diltiazem
TH production: Potassium iodide or PTU
What is the MOA of PTU in removing excess TH during a thyroid storm?
Sequester excess TH w/ bile acid (via cholestyramine) & fecal excretion or plasmapheresis
What are the 4 classes of drugs used to treat hyperthyroidism?
Thioamides
Uptake inhibitors
Radioactive Iodine
Surgical resection
What is the MOA of Thioamides?
Inhibit TPO (thyroid peroxidase enzyme)
inhibits T4 → T3 conversion in periphery
When in practice are thioamides used?
Precursor to surgical removal of thyroid
can normalize TSH levels over time
What are commmon AE of thioamides?
Goiter formation (continual thyroid stimulation via TSH)
Maculo-papular rash
arthralgia
What are the rare but severe AE of thioamides?
agranulocytosis
hepatotoxicity
ANCA-+ vasculitis
pancreatitis
How is hyperthyroidism controlled during pregnancy?
1st trimester- PTU is preferred bc higher plasma binding
2nd/3rd trimester- Methimazole preferred bc PTU can cause hepatotoxicity
What is the MOA of Iodine uptake inhibitors (NIS)?
inhibit sodium-Iodine transporter
When are iodine uptake inhibitors used?
hyperthyroidism via other drug interactions (ex amiodarone has iodine and can increase uptake)
Perchlorate rarely used bc risk of aplastic anemia
What drug class does Perchlorate belong to?
Iodine Uptake inhibitors (NIS)
When is radioactive iodine CI and why?
Pregnant and lactating women
risk of fetal thyroid destruction
What is the only form of radioactive iodine?
Iodine 131
What is the MOA of radioactive iodine?
concentrates in thyroid follicle & destroys cells
(epithelial swelling, necrosis, follicle disruption, edema, leukocyte infiltration)
What is Iodide 127 and what is the MOA?
Lugol’s solution
non-radioactive
inhibits TH synthesis via Wolff-Chaikoff effect
What other medications can inhibit peripheral T4 → T3?
Contrast media: Ipodate & Iohexol
Beta-blockers
Corticosteroids
Tyrosine Kinase Inhibitors
Lithium
How do beta-blockers inhibit peripheral T4 → T3?
TH increases expression of B-AR
Hyperthyroidism resembles non-specific SNS stimulation
How do corticosteroids inhibit peripheral T4 → T3?
inhibits 5’-deiodinase, decreases peripheral T3 production
How do TKIs inhibit peripheral T4 → T3?
Sunitinb
causes hypothyroidism as expected ADR
How does Lithium inhibit peripheral T3 → T4?
inhibits coupling of iodotyrosine to decrease T4 production & release
What are 3 primary causes of hypothyroidism?
Hashimoto’s disease
Iatrogenic hypothyroidism
Less common: iodine deficiency, enzyme defects, thyroid hypoplasia, goitrogens
When it is appropriate to treat hypotyroidism?
ELEVATED TSH
w/ normal or low free T4
Why is T4 preferred for hypothyroidism supplementation?
Longer T 1/2 → allows for less dosing throughout day (7 days) → improves adherence
Predictable PK
What is thyroid USP made of and what is its thyroid ratio?
desiccate pork thyroid gland
High T3:T4 (4:1)
inexpensive
What is levothyroxine made of?
Synthetic T4
What is Liothyronine made of and what is is T 1/2?
Synthetic T3
rapid onset
T 1/2 = 1.5 days
What is Liotrix made of and what is the thyroid ratio?
Synthetic T4 & T3 (4:1)
risk of T2 thyrotoxicosis bc high ratio of T3 to T4
Note
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