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Endocrine II midterm > Kruse DSA: Drugs for Thyroid Disorders > Flashcards

Kruse DSA: Drugs for Thyroid Disorders Flashcards

1
Q

The Thyroid Agents?

A
  • levothyroxine (T4)
  • Liothyronine (T3)
  • Liotrix (a 4:1 ratio of T4:T3
  • Thyroid desiccated
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2
Q

Antithyroid agents

A
  • Radioactive iodine (131 I) sodium
  • Methimazole
  • Potassium iodide
  • propylthiouracil (PTU)
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3
Q

Whta is an essential element in the making of thyroid hormone?

A
  • Iodine

- unabsorbed iodide is excreted in the urine

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4
Q

What transports iodide into the thyroid gland?

A

NIS

-sodium/iodide symporter

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5
Q

What is Pendrin

A
  • an apical cell iodide transport enzyme
  • controls the flow of iodide across the membrane
  • also in cochlea…. if we don’t have it, deafness and goiter= Pendred syndrome
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6
Q

What is Iodide oxidized by at the apical cell membrane?

A

thyroidal peroxidase

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7
Q

What is is called when iodine rapidly iodinates tyr residues within the thyroglobulin molecule to form MIT and DIT?

A

iodide organification

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8
Q

What is Thyroglobulin

A

-a large glycoprotein that contains about 70 tyr aa’s, which are the major substrates that combine with iodine to form the thyroid hormones

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9
Q

what do 2 DIT molecules combine to make?

A

thyroxine T4

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10
Q

What is made when one DIT and one MIT combine?

A

triiodothyronine (T3)

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11
Q

What is the T4:3 ratio withing the thyroid gland?

A

5:1

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12
Q

What are some things that will block the conversion of T4 to T3?

A
  • radiocontratst media
  • B-blockers
  • corticosteroids
  • amiodarone
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13
Q

Thyroid hormone transport

A
  • T4 and 3 bine to TBG in plasma

- free levels of thyroid hormone is low

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14
Q

Peripheral metabolism of thyroid hormones

A

T4 gets turned to T3 (2 kinds)

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15
Q

Which T3 is the metabolically inactive one?

A

3,3,5-triiodothyronine (reverse T3

-3,5,3-“ “ is the one that does stuff

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16
Q

How is T4 inactivated?

A
  • deamination
  • decarboxylation
  • conjugation
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17
Q

When is the half life of T4 and 3 decreased and the clearance increase?

A

in hyperthyroidism patients

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18
Q

What are some agents that inhibit the conversion of T4 to T3 and increase reverse T3 levels?

A
  • radiocontrast agents: iopanoic acid, ipodate
  • amiodarone
  • B-blockers
  • corticosteroids
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19
Q

When would we use the things that inhibit T4 to T3 conversion?

A

-to reduce T3 levels in pts who are experiencing a thyroid storm

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20
Q

What are drugs that decrease T4 absorption

A
  • antacids
  • ferrous sulfate
  • cholestyramine
  • colestipol
  • ciprofloxacin
  • proton pump inhibitors
  • bran
  • soy
  • coffee
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21
Q

What is the significance of drugs that induce hepatic CYP450s?

A

-increase the metabolism of T4 and T3

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22
Q

What drug conditions will give us an alteration of T4 and T3 metabolism with modified serum T3 and T4 levels, but not free T4 or TSH?

A
  • induction of increased hepatic enzyme activity

- inhibition of 5’-deiodinase with decreased T3 and increased reverse T3

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23
Q

What drugs are involved with induction of increased hepatic enzyme activity?

A
  • Nicardipine
  • imantinib
  • protease inhibitors
  • phenytoin
  • carbamazepine
  • phenobarbital
  • rifampin
  • rifabutin
24
Q

What drugs are involved witih the inhibition of 5”-deiodinase with decreased T3 and increased reverse T3

A
  • Ipopanoic acid
  • Ipodate
  • Amiodarone
  • B-blockers
  • Corticosteroids
  • PTU
  • flavonoids
25
Q

What drugs cause induction of autoimmune thyroid disease with hypothyroidism or hyperthyroidism?

A
  • Interferon-alpha
  • IL-2
  • IFN-B
  • lithium
  • amiodarone
26
Q

MOA for the thyroid hormone

A
  • thyroid receptor is bound to DNA at the TRE
  • no hormone, it’s a homodimer bound to corepressor ptns and is inactive
  • T4 and T3 enter cell by active transport and T4 is converted to T3 by 5’-deiodinase
  • T3 enters nucleus, binds TR, corepressor releases, coactivator binds, homodimer separates, TR bind to RXR (retinoid X receptor), and gene transcription occurs
27
Q

What is the preparation of choice for thyroid hormone?

A

levothyroxine (T4)

28
Q

What are the Thioamides again?

A
  • antithyroid agents
  • Methimazole
  • PTU
29
Q

PK of PTU

A
  • renal excretion a lot
  • accumulates in thyroid gland
  • shorter half life than methimazole
  • 3-4 doses/day
30
Q

PK of Methimazole

A
  • completely aborbed
  • accumulates in thyroid galnd
  • slower renal excretion than PTU
  • half life 6 hrs
  • once-daily dosing
31
Q

Why is methimazole agents not recommended in preggo?

A

-cross placental barrier and concentrated by fetal thyroid

32
Q

How do we treat a preggo women then who have hyperthyroidism?

A
  • PTU in the first trimester
  • Methimazole in 2nd and 3rd trimesters
  • secreted in breast milk at low concentrations and considered safe
33
Q

MOA of antithyroidal agents

A
  • inhibits the thyroidal peroxidase-catalyzed rxns and blocks iodide organification
  • also inhibits couple of MIT and DIT
34
Q

What does PTU do?

A

blocks peripheral conversion of T4 to T3
-significantly greater fall in T3 concentration and T3:T4 ratio may occur with PTU and iodine compared to methimazole and iodine

35
Q

Do thioamides block thyroid gland iodide uptake?

A

no

36
Q

since the hormone synthesis, rather than release, is inhibites, how long will it take before the stores of T4 and T3 are depleted?

A

3-4 weeks

37
Q

Toxicity of Thioamides?

A
  • most common are maculopapular pruritic rash, at times accompanied by systemic signs such as fever, nausea, and GI distress
  • most serious complication is agranulocytosis, can be reversed with drug discontinuation and CSFs
38
Q

Anion inhibitors

A

-monovalent anions: perchloratem, pertechnetate, and thiocyanate

39
Q

MOA of anion inhibitors

A

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

  • effects can be overcome by large doses of iodides
  • effects are unpredictable and clinical usefulness is limites
40
Q

Iodides MOA

A

-inhibit organification and hormone release; decrease the size and vacularity of the hyperplastic thyroid gland

41
Q

clinical use of iodide

A
  1. ) thyroid storm- thyrotoxic symptoms improve rapidly (within 2-7 days)
  2. ) preoperative reduction of a hyperplastic thyroid gland
  3. ) block thyroidal uptake of radioactive isotopes of iodine in a radiation emergency or other exposure to radioactive iodine
42
Q

Toxicity of Iodides

A

-Adverse rxns are uncommon, but include acneiform rash, swollen salivary glands, mucous membrane ulcerations, conjunctivitis, metallic taste

43
Q

When should Iodides be avoided?

A
  • during preggo

- iodides can cross the placenta and cause fetal goiter

44
Q

Radioactive Iodine

A
  • 131 I
  • orally
  • destruction of thyroid parenchyma: epithelial swelling and necrosis, follicular disruption, edema, and leukocyte infiltration
  • contraindicated in women who are preggo or breast feeding
45
Q

B-blockers

A
  • good for managing thyrotoxicosis because a lot of the thyroid hormone effects are in line with sympathetic effects
  • “olol”s, propanolo is commonly used
  • do not alter thyroid levels
  • high doses can reduce T3 levels by blocking the peripheral conversion of T4 to T3
46
Q

What is the drug of choice for replacement thyroid replacement therapy?

A

levothyroxine

  • child need more than adults
  • should be given on an EMPTY STOMACH
  • 6-8 weeks to reach stead-state levels
47
Q

What do we do for pts who are in a mysedema coma?

A
  • give it IV

- large loading dose of T4 followed by smaller IV dosing

48
Q

What about for mysedema and cornary artery disease

A

-correction of myxedema with T4 must be done cautiously to avoid provoking arrhythmia, angina, or acute MI (those are all related to high T4 levels)

49
Q

What sucks about women who are hypthyroid?

A

they are typically infertile until restoration of normal thyroid levels
-maintenance of normal levels is crucial due to fetal brain development dependence on maternal T4*

50
Q

What do we give someone who has Grave’s disease?

A

-methimazole or PTU until remission (12-18 months)

51
Q

Which one is preferred, methimazole or PTU?

A

methimazole due to once-daily administration

52
Q

What is the tx of choice for pts with very large glands or multinodular goiters

A

thyroidectomy

-will probably require thyroid supplementation

53
Q

What is radioactive iodine the preffered treatment in?

A
  • for most patients over 21
  • in pts with underlying heart disease or severe thyrotoxicosis and in elderly patients, tx with antithyroid drugs until the patients is euthyroid is preferable
  • 80% will develop hypothyroidism and require replacement therapy
54
Q

What are some adjuncts to antithyroid therapy?

A
  • administration of B-blockers without intrinsic sympathomimetic activity is beneficial
  • B-blockers can control tachycardia, htn, and atrial fibrillation
  • Diltiazem (calcium-channel blocker) can be used to manage tachycardia in patients in whom B-blockers are contraindicated
55
Q

What do we do if someone is having a thyroid storm (thyrotoxic crisis)?

A
  • B-blockers to control the arrhythmia
  • potassium iodide to prevent release of thyroid hormones from the thyroid gland
  • PTU or methimazole to block hormone synthesis
  • IV hydrocortisone to protect against shock and to block the conversion of T4 to T3 in peripheral tissues/blood
  • Supportive therapy to control any underlying issues
56
Q

What do we do for thyroid storm if everything else is inadequate?

A

-plasmapheresis or peritoneal dialysis may be used to lower the levels of circulating T4

Endocrine II midterm (13 decks)

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