Thyroid Drugs

Question 1

MOA of levothryoxine?

Answer 1

synthetic T4. Higher doses required in children and may take several weeks for steady state to be reached.

Question 2

MOA of liothyronine

Answer 2

synthetic T3.

Question 3

MOA of methimazole

Answer 3

thioureylene. Inhibits iodine organification (peroxidase catalyzed reactions of iodination and coupling). 10x more potent than PTU. Crosses placenta and concentrated in fetal thyroid.

Question 4

ADE of methimazole

Answer 4

Crosses placenta and concentrates in fetal thyroid. Can be transferred through breast milk to infants.

Agranulocytosis and skin rash.

Question 5

MOA of propylthiouracil

Answer 5

AKA PTU. thioureylene. Inhibits iodine organification (peroxidase catalyzed reactions of iodination and coupling). Also inhibits peripheral T4 to T3 conversion. Rapidly absorbed and shorter half-life.

Question 6

ADE of proylthiouracil

Answer 6

agranulocytosis and skin rash

Question 7

ADE of radioactive iodine contrast

Answer 7

can cause thyroid storm in hyperthyroid patients or incident hyperthyroidism in normal individuals

Question 8

Which enzyme converts T4 to T3?

Answer 8

5’-deiodinase.
In liver kidney and thyroid Type I (D1)
Brain, pituitary, heart, skeletal muscle have D2 isoform.

Question 9

What enzyme forms rT3?

Answer 9

thyronine 5-deiodinase found in placenta, skin and brain. rT3 is an inactive form.

Question 10

What is transthyretin (TTR)?

Answer 10

binds 2:1, T4:T3. frormerly called prealbumin.. Higher levels of TTR than TBG but TBG binds most. Also transports T4 into CSF

Question 11

What is myxedema indicative of?

Answer 11

hypothyroidism

Question 12

MOA of radioactive iodine Na131I treatment?

Answer 12

beta radiation will destroy all or part of parenchymal cells in thyroid tissue.

Question 13

ADE of radioactive iodine Na131I treatment?

Answer 13

no evidence of radiation damage in any other tissues.