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Drug Action II > Block 4: Thyroid Med Chem > Flashcards

Block 4: Thyroid Med Chem Flashcards

1
Q

What is the major function of the thyroid?

A

Only organ in mammals capable of incorporating iodine into organic substances

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2
Q

What are the fundamental hormones of the thyroid?

A
  1. Thyroxine (T4)
  2. Triiodothyronine (T3)
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3
Q

What is the function of T3 and T4?

A
  1. Vital for normal growth and development
  2. Control energy metabolism and protein synthesis
  3. Maintaining homeostasis
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4
Q

Describe the structure of TH?

A

Iodinated aa derived from L-tyrosine

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5
Q

How is T3 synthesized?

A
  1. T4 by deiodinase enzymes outside of the thyroid
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6
Q

What causes a large goiter?

A

Increased TSH

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7
Q

What are the isoforms of deiodinase?

A

D1: Non selective
D2: Removes outer 5’ only, priming activation
D3: removes inner only, primary inactivation

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8
Q

Where does TH activation occur?

A

Occurs in the periphery

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9
Q

What element is in deiodinase?

A

Selenium

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10
Q

Why is amiodarone CI with thyroid?

A
  1. Non-selective deiodinase activity can release free iodine -> ↑ free iodine 20-40%
  2. Displaces TH from deiodinase -> hypothyroidism
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11
Q

What is the MOA of thyroid peroxidase?

A

Iodide -> I2 -> I radical -> tyrosine -> coupled building blocks -> release alanin

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12
Q

What are the building blocks of T3 and T4?

A

MIT+DIT for T3
DIT and DIT for T4

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13
Q

What are the other forms of iodothyronines?

A

T2 and rT3:
1. Not responsible for physiological effects
2. Results from nonselective deiodinase activity

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14
Q

What are thyroglobulin?

A

Large glycoprotein that accounts for about 1/3 of the total weight of thyroid gland

Carries 6 tyrosil residues as MIT and 5 residues as DIT

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15
Q

What are the types of replacement therapies?

A

Naturally derived or synthetic

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16
Q

What is the MOA of replacement therapy?

A
  1. Prevention iodide uptake into follicular cells
  2. Inhibiting TPO
  3. Prevention of thyroid hormones binding to plasma proteins
  4. Effectors of thyroid deiodinases
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17
Q

Describe the preparation of natural thyroid products?

A
  1. Desiccated thyroid and thyroglobulin derived from glands of domestic animals that are used for food
  2. Active hormones are released by the proteolytic activity of gut enzymes
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18
Q

Potency of thyroid preps are based on?

A

Total iodine content determined by bioassay

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19
Q

What is Thyroid USP?

A
  1. PO desiccated thyroid preps that are acetone powders of bovine and porcine
  2. Diluent is commonly incorporated because prep often exceeds 0.17-0.23% iodine requirements
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20
Q

What is the porportion of Armor Thyroid?

A

4.22:1 (T4/T3)

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21
Q

What are the synthetic formulations TH?

A
  1. T4 (levothyroxine)
  2. T3 (liothyroxine)
  3. dT4 (dextrothyroxine)
  4. Mixture (Liotrex)
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22
Q

T4 forumulation?

A

(Levothyroxine, Synthroid):
Synthetic, crystalline form of levo-T4 that is a great binder to carrier proteins

23
Q

PK of Synthroid?

A
  1. Slower onset of action due to required metabolism to T3
  2. Greater increase in serum T4 levels but a lesser increase in serum T3 levels than Thyroid USP.
24
Q

T3 formulation

A

(Liothyronine)
Rapid onset of action and short DOA

Therapy of choice for patients with heart disease due to rapid onset

25
Q

What is Liotrix?

A

Synthetic armor thyroid:
Mixture of both synthetic T3 and T4 as their crystalline sodium salts

4:1 ratio (T4:T3)

26
Q

What is radioiodine?

A

All isotopes of iodine are rapidly taken up by the thyroid into thyroid follicles

27
Q

What is the importance of 131I isotope?

A

Decays primarily to 131Xe with emmission of b particle and V yrays

28
Q

What I isotope does not produce a B-particles?

A

125I isotope decays to 125Te

29
Q

What occurs after absorption of 131b particle radiation?

A

Localized destruction of thyroid follicles and deep tissue damge

30
Q

What are the most common ionic agents for thyroid imaging?

A

Perchlorate and Pertechnetate: Large anions that can be take up by the thyroid via iodide pump (Na/I symporter)
1. Greater affinity over I
2. Do not incorporate into thyroglobulin

31
Q

Why was percholate use DC’d?

A

Risk of aplastic anemia

32
Q

What is purpose of administerating I?

A

Inhibits the release of thyroid hormone, which serves as the basis for its use in hyperthyroidism.
1. Iodide decrease the vascularity of the enlarged thyroid and also lowers the elevated BMR
2. Excess iodide might change the conformation of thyroglobulin making it less susceptible to thyroidal proteolysis

33
Q

What is lugol’s solution?

A

Strong iodide solution USP (SSKI) used 2 weeks prior ro thyroid surgery:
* Decreases the vascularity and makes the gland more defined and firm

34
Q

What are the ADRs of lugols?

A
  1. Allergic reaction
  2. dermatological and cold-like symptoms
  3. Strong expectorant
35
Q

What are thionamide?

A

Nondestructive therapy of hyperthyroidism

36
Q

What are the types of thionamides?

A
  1. Propylthiouracil (PTU)
  2. Methimazole (MMI)
37
Q

What is the MOA of thionamides?

A

Potent inhibitors of TPO without affecting iodide pumps or thyroid hormone relase

38
Q

What is TPO?

A

Responsible for the iodination of tyrosine residues in thyroglobulin as well as the coupline of iodotyrosines to form iodothyronines

39
Q

How did they improve MMI adherence?

A

Carbimazole was developed as a prodrug to improve taste and afford CR of methimazole

40
Q

What is the tx of thyrotoxicosis?

A

Thyrotoxicosis is adrenergic overstimulation requiring adrenergic blockade:
1. Reserpine and guanethidine to deplete catecholamine stores
2. Beta blockers have been used to prevent tachycardia, tremor, anxiety, and hypertension

41
Q

What is the preventative therapy for acute thyrotoxicosis?

A

Beta blockers

42
Q

What is goitrogens?

A

Found in sulfur containing compounds that contributes to thyroid dysfunction and goiter formation

43
Q

What are the forms of goitrogens?

A
  1. Goitrin: found in cruciferous veggies and most common
  2. Thiocyanates
44
Q

Describe the differences between the goitrogens?

A

Thiocyanates: large anions that compete for iodide for uptake by thyroid gland (reversible by iodide intake)
Goitrin: potent thyroid peroxidase inhibitor that is more potent than PTU in humans

45
Q

How does heparin affect thyroid function?

A

Interfere with the binding of T4 to plasma transport proteins due to its anionic sulfate

46
Q

How does warfarin and dicoumarol effect thyroid function?

A

Competitive inhibitors of T4 in the reaction required for its conversion to T3

47
Q

What drugs interfere with the peripheral deiodination of T4?

A

Amiodarone and iopanoic acid

48
Q

Too little GH?

A

Pituitary dwarfism

49
Q

Too much GH?

A

acromegaly gigantism

50
Q

What are the GH inhibitors?

A
  1. Somatostatin
  2. Octreotide
  3. Pegvisomant
51
Q

What are somatostatin?

A

Inhibits the release of hGH from the anterior pituitary, too short t 1/2

52
Q

What is octreotide?

A

Suppresses the secretion of gastroenteropancreatic peptides, such as gastrin, vasoactive intestinal peptide (VIP), insulin and glucagon, as well as hGH from the pituitary

53
Q

What is pegvisomant?

A
  1. Recombinant hGH with the identical aa sequence as endogenous hGH but its pegylated
  2. Used in patients with acromegaly who have not responded well to surgery/radiation

Drug Action II (28 decks)

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