Thyroid

Question 1

Wolf chaikoff Effect:

Answer 1

excess iodide can block production and release of t4/t3 for ~10 days. But escape mechanisms can occur after 10 days.

Question 2

path

Answer 2

I-+sodium iodide symporter → iodide into T gland thyroid peroxidase turns I- to I0 → MIT and DIT, T3-T4 → to blood and peripheral tissues

Question 3

stress blocks…

Answer 3

TRh and TSH

Question 4

T3:

Answer 4

more potent than T4, bound to TBG. 80% of T3 comes from T4

Question 5

High D1

Answer 5

hyperthyroidism as it metabolizes 40%
D3: 20%, D2 also 40%, depends on part of body
T4: degrades D2

Question 6

Factors on binding thyroxine to TBG:

Answer 6

drugs like heroin, tamoxifen, estrigens, 5FU incrwase, antiseizure meds, androgens, corticosteroids decrease binding

Question 7

drug interactiosn of hyperthyroidism

Answer 7

decreases vit k dependent clotting, so lower doses of warfarin

Question 8

Myxedema:

Answer 8

underactive thyroid

Question 9

Hypothyroidism:

Answer 9

underactive thyroid hormone like T4. Tx via synthetic thyroxine

Question 10

Levothyroxine:

Answer 10

T4. for congenital or acquired hypothyroidism, adjuvant for thyroid cx. Low TI.AA: Angina, worse glycemic control, bone resorption

Question 11

Triiodothyronine:

Answer 11

T3. Adjuvant tx, not for routine replacement. More potent, also a diagnostic agent for mild hyperthyroidism. AA: be careful with heart disease. IV normally but can be oral.

Question 12

Hyperthyroidism

Answer 12

overactive thyroid hormone

Question 13

Amiodarone:

Answer 13

antiarrhythmic drug blocks peripheral conversion of T4 → T3. Thyrotoxicosis may develop.

Question 14

Lithium:

Answer 14

Impairs uptake of iodine, blocks organification, impairs release of T3/T4 from gland. Off label refractory hyperthyroidism. AA: hypothyroidism

Question 15

Radioactive iodine (I131):

Answer 15

gets absorbed by thyroid gland, the radiation in it destroys cancerous
and normal thyroid cells.

Question 16

Propylthiouracil (PTU):

Answer 16

inhibitor of D1 conversion and synthesis of thyroxine. Blocks production of T3. AA: agranulocytosis, high liver enzymes, severe hepatitis.

Question 17

Methimazole:

Answer 17

inhibits thyroid peroxidase, longer hL from PTU. AA: GI distress, rash, agranulocytosis, jaundice, elevated liver enzymes, hepatic toxicity

Question 18

Lugol’s solution, potassium iodide:

Answer 18

inhibits organification and T3/T4 release. Dont use with Radioactive
Iodine. AA: bleeding dx, rash, swollen glands, metallic taste, ulcers in membranes. Not sole tx.

Question 19

Thyroid storm: acute exacerbation. Treatments for thyroid storm(the five Bs).

Answer 19

block synthesis
block peripheral effects,
block enterohepatic recirculation
lower HR and CO
block release (and synthesis of TH)

Question 20

Thyroid storm drugs

Answer 20

PTU PO or rectally: block synthesis

KI-:block release (and synthesis)

Hydrocortisone: block peripheral effects, block T4 to T3(release of tsh, t4 to t3).

Bile sequestrants: block enterohepatic recirculation(lowers circulating thyroxine).

Propranolol and metoprolol: beta adrenergic receptor antagonists to lower HR and CO
Diltiazem, verapamil: calcium channel blockers if P and M cannot be used