Thyroid Pharmacology

Question 1

Does T3 or T4 have a shorter half life?

Answer 1

• T3= 1 DAY (compared to T4= 1 week)

* important because you will give T3 to someone in a hypothyroid state.

Question 2

What is responsible for regulating the conversion of T4 to T3 in the periphery?

Answer 2

• deiodinase-1 (D1)= a peroxidase enzyme that is involved in the activation or deactivation of thyroid hormones.
• D2 is the same, but found only in the brain.

Question 3

To what do T3 and T4 bind in the blood in order to be transported?

Answer 3

• thyroxine-binding globulin (TBG)

* tranthyretin only binds T4

Question 4

How do you distinguish between primary, secondary, and tertiary HYPOthyroidism?

Answer 4

• PRIMARY= TH deficiency (TH levels do NOT increase with administration of TSH). Ex. Hashimotos
• SECONDARY= TSH deficiency (TSH levels do NOT increase with administration of TRH). Ex. Sheehan’s
• TERTIARY= TRH deficiency (increased TSH levels with administration of TRH).

Question 5

** What is the most common drug replacement hormone for HYPOthyroidism?

Answer 5

• LEVOTHYROIXINE sodium (T4)

* used over liothyronine sodium (T3) bc it has a much longer half life.

Question 6

Is there an advange to combining T4/T3 to treat hypothyroidism?

Answer 6

• not really.

Question 7

What is an ADR of Levothyroixine?

Answer 7

• hyperthyroidism if you give too much.

Question 8

What are the limited uses of Liothyronine (T3)?

Answer 8

• T3 suppression to differentiate hyperthyroid from euthyroidism.
• short term supppresion of a solitary thyroid nodule before radioactive iodine scan.

Question 9

What is Thyrotoxicosis (hyperthyroidism); Grave’s disease?

Answer 9

• antibody against the TSH receptor, leaing to a toxic multinodular goiter

Question 10

How do you treat Thyrotoxicosis (hyperthyroidism); Grave’s disease?

Answer 10

• inhibit thyroidal secretion via surgery or radiation.

Question 11

** How do you treat thyroid storm (potentially fatal thyrotoxic crisis)?

Answer 11

• sedation, O2, decrease body temp, antithyroid meds, iodine, CORTICOSTEROIDS, fluids, electrolytes, and B-BLOCKERS.

Question 12

What are the antithyroid agents?

Answer 12

• Methimazole
• Polythiouracil (PTU)
• Potassium perclorate (KCLO4)
• Potassium iodide (KI)
• Iodine 131
• B-adrenergic blockers (PROPRANOLOL)

Question 13

** What is Methimazole?

Answer 13

• inhibitor of iodine incorporation to tyrosine residues (MIT and DIT).
• preferred over PTU to treat hyperthyroidism (lower risk of liver injury).
• similar to PTU but no inhibition of T4 to T3 in periphery.

Question 14

What is an ADR of Methiomazole?

Answer 14

• AGRANULOCYTOSIS

Question 15

** What is Propylthiouracil (PTU)?

Answer 15

• same as methimazole, but also inhibits T4 to T3 in periphery.
• shorter half life than Methimazole.

Question 16

What ADR does PTU have in addition to agranulocytosis (like Methimoazole)?

Answer 16

• severe HEPATITIS

Question 17

Are Methiomazole and PTU contraindicated in pregnancy?

Answer 17

• YES (DO NOT USE)

Question 18

What is Potassium perchlorate (KClO4)?

Answer 18

• interferes with Iodide transport into thyroid gland, but not used much anymore bc it can cause severe aplastic anemia.

Question 19

** What is Potassium Iodide (Lugol’s solution)?

Answer 19

• transiently inhibits organificaiton (iodine formation).
• inhibits hormone release.
• inhibits accumulation of radioiodine.
• used as PREOPERATIVE PREPARATION for THYROIDECTOMY and for THYROID STORM.

Question 20

** What will Iodine 131 (radioactive) do?

Answer 20

• PERMANENTLY reduces TH production.

* mainly used for pts with Grave’s disease

Question 21

Why would we use a Beta blocker during thyrotoxicosis?

Answer 21

• to decrease hyperthyroid-induced tachycardia, tremor, sweating, heat intolerance, and anxiety.

Question 22

What are the contraindications for Beta-blockers (propranolol)?

Answer 22

• obstructive airway disease (blocks bronchodilation).

- causes hypoglycemia in diabetics.