thyroid and antithyroid agents

Question 1

actions of thyroid hormones

Answer 1

• *increase BMR
• *increase HR and CO
• *stim PRO synthesis, a process essential for growth and development
• stim CHO metabolism and lipolysis
• reduce insulin sensitivity
• thyroid hormones contain iodine and that is one fo the reasons why iodide is a dietary req

Question 2

perchlorate

Answer 2

can inhibit uptake of iodide into thyroid follicular cells

Question 3

propylthiouracil (PTU) MOA

Answer 3

rx of thyperthyroidism

• thioamide
• inhibit thyroid peroxidase thus decreasing the oxidation of iodide, iodination of thyroglobulin, and coupling of MIT and DIT to form T3/T4
• also inhibits peripheral conversion of T4 to T3
• slow course of action bc thyroid hormone stores take time to be depleted

Question 4

methimazole (MMI) MOA

Answer 4

rx of thyperthyroidism

• thioamide
• inhibit thyroid peroxidase thus decreasing the oxidation of iodide, iodination of thyroglobulin, and coupling of MIT and DIT to form T3/T4
• slow course of action bc thyroid hormone stores take time to be depleted

Question 5

SE of MMI and PTU

Answer 5

-skin rashes, delayed hypothyroidism, agranulocytosis

Question 6

which hyperthyroid agent is tried first? which is faster

Answer 6

MMI; PTU is faster but is less potent and has shorter DOA

Question 7

pregnancy and hyperthyroidism

Answer 7

-rx with PTU instead of MMI during 1st trimester, can be switched afterwards; both safe for lactation

Question 8

PTU/MMI dosing

Answer 8

• start high and shift low
• incidence of relapse is as high as 50%, but depends on onset of treatment, severity of disease, and iodide content of diet

Question 9

potassium iodide MOA, course of action

Answer 9

2-iodide
inhibits release of t3 and t4
-course of action is fast (days), but effect is transient (2-8 weeks)
-rarely used as sole therapy

Question 10

potassium iodide SE

Answer 10

• safe/reversible
• rashes and swollen salivary glands (also have iodide transporters)
• used to prevent uptake of I131 after a nuclear accident

Question 11

I-131

• MOA
• SE

Answer 11

-concentrates in the thyroid and causes localized radiation damage
-oral admin
-delayed hypothyroidism, radiation exposure
-course of action is slow
NOT for use in pregnant women or nursing

Question 12

subtotal thyroidectomy

Answer 12

required in 80-90% of cases

-followed by replacement therapy to rx resulting hypothyroidism

Question 13

therapeutic choices for hyperthyroidism

Answer 13

• I 131
• Surgery
• thioamides
• iodide followed by surgery
• thioamides followed by surgery

Question 14

use of beta-adrenergic antagonists in hyperthyroidism

Answer 14

propranolol

-alleviate symptoms associated with increased CV activity

Question 15

thyroxine

Answer 15

T4, target of thyroid hormone receptor
potency 1
t1/2 7 d
oral abs 75-90%
converted to T3 in peripheral tissues
-cheaper

Question 16

triiodothyronine

Answer 16

T3 target of thyroid hormone receptor
potency 4
t1/2 1 day
oral abs 95%
-more expensive

Question 17

thyrolar (T3 +T4)

Answer 17

target of thyroid hormone receptor

Question 18

rx of hypothyroid in children versus adults

Answer 18

-need 10x more hormone/kg body weight than adults d/t growth and dev

Question 19

rx of hypothyroid in preggo

Answer 19

-higher doses and closer monitoring, CBG levels are high (lowers T3/T4)

Question 20

adverse effects of thyroid replacement

Answer 20

• thyrotoxicosis

- stress on CV system (careful if have cardiac disease)