Thyroid Drugs

Question 1

The peroxidase enzyme mediates what process? Where does this process occur?

Answer 1

Mediates the incorporation of iodide into thyrosine residues of the thyroglobulin (TG) protein. The peroxidase then mediates the coupling of iodinated thyrosines to form T3 and T4.

Thyroid gland

Question 2

Where are T3 and T4 stored?

Answer 2

Thyroid follicle cells

Question 3

What process must occur before T3 and T4 can be released into the blood?

Answer 3

Proteolysis of the thyroglobulin molecule

Question 4

Which thyroid hormone is the active hormone which is the inactive?

Answer 4

T3- active

T4- inactive

Question 5

What are the Drugs used in Hypothyroidism?

Answer 5

L-thyroxine (T4)

Triiodothyronine (T3)

Question 6

Which drug is the preferred drug in Hypothyroidism and why?

Answer 6

T4 is preferred over T3 due to its longer half-life, affordability, easier to monitor and does not have the immediate cardiovascular effects that T3 does.

Question 7

How is T3 given?

Answer 7

IV

Question 8

What can the physiologic doses of the drugs for hypothyroidism mimic? What are these symptoms?

Answer 8

Hyperthyroidism

CA effects, weight loss, osteoporosis

Question 9

What is the most common form of hyperthyroidism?

Answer 9

Graves Disease

Question 10

What is the rationale behind treating hyperthyroidism?

Answer 10

To destroy hyperactive cells or directly inhibit thyroid hormone synthesis or release

Question 11

Which disease is more difficult to treat, Hyperthyroidism or Hypothyroidism?

Answer 11

Hyperthyroidism

Question 12

What are the drugs used to treat hyperthyroidism?

Answer 12

Thioamide drugs (Methimazole and Propylthiouracil(PTU))
Radioactive iodine (131 I)
Potassium Iodide (KI)
Propanolol
Iodinated Radiocontrast Media (Ipodate)

Question 13

What are the thioamide drugs? Where do they target?

Answer 13

Methimazole and Propylthiouracil (PTU)
They both directly inhibit the peroxidase enzyme (Step 2) in T4 and T3 biosynthesis. PTU also inhibits deiodination of T4 to T3 in the liver (Step 4)

Question 14

What does PTU inhibition of the deiodinization of T4 to T3 do?

Answer 14

Blood levels of T3 decline more rapidly than T4

Question 15

When administering a thioamide drug how long should you expect the onset to be?

Answer 15

They are slow onset drugs, 2-4 weeks to become euthyroid, due to continued release of preformed T4 and T3

Question 16

What is the toxicity of the thioamide drugs?

Answer 16

Both drugs are well tolerated; skin rash is sometimes seen

Question 17

What is significant about using these drugs with Graves Disease?

Answer 17

High relapse rate due to continued auto-antibody presence/production

Question 18

What is the mechanism of Radioactive Iodine?

Answer 18

Active uptake exclusively into the thyroid follicle cells; localized tissue destruction

Question 19

Why is radioactive iodine considered a safe drug?

Answer 19

It specifically targets thyroid follicle cells which are essentially the only storage and receptor sites for iodine in the body. If there were more cells that took up iodine than the radioactive form would destroy those cells too.

Question 20

What are the contraindications of radioactive iodine?

Answer 20

Children, older patients and pregnant women (it can cross the placenta and kill the fetus)

Question 21

What are the complications of radioactive iodine?

Answer 21

Transient hyperthyroidism

permanent hypothyroidism

Question 22

Why is the permanent hypothyroidism complication preferred to hyperthyroidism?

Answer 22

It is easier to maintain and can be given T4 and monitored on this drug for life

Question 23

What is the mechanism of Potassium Iodide?

Answer 23

The “paradoxical” inhibition of iodine uptake (step 1), the peroxidase enzyme (step 2) and the proteolytic release of T3 and T4 (Step 3)

Essentially it inhibits all the processes within the thyroid gland itself

Question 24

KI is the only agent to inhibit which process?

Answer 24

The proteolytic release of T3 and T4

Question 25

What is onset and duration of KI?

Answer 25

Short term drug with only a week long effect

Question 26

Which drug is KI usually used in combination with in the treatment of Hyperthyroidism? Why?

Answer 26

KI and a Thioamide Drug are usually used in combination because of their onsets. KI can act quickly with a fast onset and when its effect wares off the Thioamides effect will be just getting started since it has a slow onset.

Question 27

When would you use propranolol in the treatment of hyperthyroidism?

Answer 27

It is used as a SYMPTOMATIC CONTROL of B-adrenergic action. It also inhibits the deionization of T4 to T3 in the peripheral tissues at high doses.

Question 28

What does Ipodate do?

Answer 28

Inhibits T4 deiodinization (Step 4) therefore rapidly decreasing T3 concentrations.

Question 29

When is Ipodate used?

Answer 29

Only if no response to other drugs

Question 30

T/F: Some drugs can alter the binding of T4 to thyroxine-binding globulin (TBG)

Answer 30

True; these drugs or hormones can mimic hyper- and hypothyroidism

Question 31

Draw out the thyroid gland and the process of synthesizing T3 from iodine. Also write out where each of the drugs discussed has its mechanism of action.

Answer 31

Do not just click to see this actually draw it out lazy