Thyroid And Anti-thyroid Drugs (Kruse)

Question 1

Describe T4 and T3 clearance and half life in pts with hyperthyroidism

Answer 1

Clearance=increased

Half life=decreased

Question 2

Describe T4 and T3 clearance and half-life in pts with hypothyroidsm

Answer 2

Clearance=decreased

Half-life=increased

Question 3

What effect do antacids, ferrous sulfate, cholestyramine, colestipol, ciprofloxacin, PPIs, bran, soy, and coffee have on T4 absorption?

Answer 3

Decrease

Question 4

Rifampin, rifabutin, phenobarbital, carbamazepine, phenytoin, imatinib, and protease inhibitors have what effect on metabolism of T4 and T3?

Answer 4

Increase –> these are all P450 inducers

Question 5

What effects will Iopanoic acid, ipodate, amiodarone, B blockers, corticosteroids, PTU, and flavonoids have on thyroid function?

Answer 5

Inhibition of 5’-deiodinase with decreased T3 and increased Reverse T3

Question 6

IFN-a, IL-2, IFN-b, Lithium, and amiodarone can have what effect on thyroid function?

Answer 6

Induction of autoimmune thyroid disease with hypothyroidism or hyperthyroidism

Question 7

Of the T4 and T3 preparations available, ___ is the preparation of choice for thyroid replacement therapy d/t its stability, low cost, lack of allergic foreign protein, easy lab measurement of serum levels, and long half-life, which permits once-daily admin

Answer 7

Levothyroxine (T4)

Question 8

Why T4 preparations over T3?

Answer 8

Although T3 is 3-4x more potent than T4, not recommended for routine therapy d/t short half life, higher cost, difficulty of monitoring its adequacy of replacement by conventional lab tests

T3 best used for short-term suppression of TSH

Question 9

This thyroid agent is a 4:1 ratio of T4:T3

Answer 9

Liotrix

Question 10

Methimazole and PTU are what type of antithyroid agents?

Answer 10

Thioamides

Question 11

Rate of absorption of thioamides? Excretion? Half life? Dose/day?

Answer 11

Rapidly absorbed
50-80% bioavailability
Renal excretion
Half life 1.5 hrs
3-4 doses/day

Question 12

This thioamide is not recommended in pregnant women. It is secreted in breast milk at low concentrations and considered safe

Answer 12

Methimazole

Question 13

Main MOA of thioamides?

Answer 13

Inhibits the thyroidal peroxidase-catalyzed rxns and blocks iodide organification; also inhibits coupling of MIT and DIT to form T3 and T4

Question 14

__ blocks peripheral conversion of T4 to T3. A significantly greater fall in [T3] and the T3:T4 ratio may occur with PTU and iodine compared to methimazole and iodine

Answer 14

PTU

Question 15

Most common adverse effects of thioamides?

Answer 15

Maculopapular pruritic rash, at times accompanied by systemic signs such as fever, nausaea, and GI distress

Question 16

Most serious complication associated with thioamides?

Answer 16

Agranulocytosis. Can be reversed with drug discontinuation and CSFs

Question 17

Perchlorate, pertechnetate, and thiocyanate are these types of drugs:

What is their MOA?

Answer 17

Anion inhibitors

Block thyroid gland uptake of iodide by competitively inhibiting the iodide transport mechanism

Effects can be overcome by large doses of iodides

Question 18

MOA of Iodides?

Answer 18

Inhibit organification and hormone release; decrease size and vascularity of the hyperplastic thyroid gland

Question 19

Clinical use of iodides?

Answer 19

Thyroid storm
Preoperative reduction of hyperplastic thyroid gland
Block thyroidal uptake of radioactive isotopes of iodine in a radiation emergency or other exposrue to radioactive iodine

Question 20

When should iodides be avoided?

Answer 20

During pregnancy –> can cross placenta and cause fetal goiter

Question 21

__ is the only isotope used for tx of thyrotoxicosis

Answer 21

131-Iodine –> radioactive iodine

Question 22

Contraindication of radioactive iodine?

Answer 22

Women who are pregnant or breast feeding

Question 23

Propanolol (most common), metoprolol, and atenolol can be used in management of___

Answer 23

Thyrotoxicosis

Question 24

Food or no food with levothyroxine?

Answer 24

Take on empty stomach

Question 25

Why do you need to be careful when giving T4 to pts with myxedema and CAD?

Answer 25

Avoid provoking arrhythmia, angina, or acute MI

Question 26

This anti-thyroid is preferred for Graves (hyperthyroidism/thyrotoxicosis)

Answer 26

Methimazole

Question 27

Adjuncts to antithyroid therapy?

Answer 27

B blockers

Diltiazem (CCB) can be used to manage tachycardia in pts whom B blockers are contraindicated

Question 28

In thyroid storm:

__ can be used to control arrhythmia
__ to prevent release of thyroid hormones form thyroid gland
__ to block hormone synthesis
__ to protect against shock and to block conversion of T4 to T3 in peripheral tissues/blood

Answer 28

B blockers
Potassium iodide
PTU or Methimazole
IV hydrocortisone