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Pharm final > Thyroid and anti thyroid hormones > Flashcards

Thyroid and anti thyroid hormones Flashcards

1
Q

how does thyroxine improve BMR

A

via Na/K ATPase activity.

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2
Q

which has greater affinity to receptors between T3 AND T4?

A

T3 10 times more potent

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3
Q

Mechanism of action of thyroid hormones:

A
  • Signaling mechanism is via TRH –IP3 mediated; TSH –cAMP mediated and the T3 & T4 binds with the receptor in the nucleus.
  • Mechanism: binds with intracellular receptors that control the gene expression with RNA formation and protein synthesis.
  • Proteins synthesized depends on tissues involved e.g., Na+/K+ ATPase and β1 receptor in the heart; enzymes for the lipid metabolism and developmental components for the brain etc.
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4
Q

Thyroid hormone Preps:

AE

A
  • Levothyroxine (T4) longer t ½ ; (T4 is converted to T3 in target tissues such as liver, kidneys etc.)
  • Liothyronine (T3) short t ½; (T3 is 10 X more potent than T4)
  • Thyroid hormone-Uses:
  • Cretinism (due to thyroid hormone synthesis enzyme defect)
  • Adult hypothyroidism (Myxedema)
  • AE: Tremors, tachycardia, arrhythmias and heat intolerance
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5
Q

Enzyme induction by what drugs can increase metabolism of the thyroid hormones - T3 T4?

A

Rifampin, Phenobarbital and Phenytoin

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6
Q

Drugs used in hyperthyroidism

A

Thioamides (goitrogens)
- Propythiouracil, Methimazole

Iodine and Iodide salts
•Lugol solution, Potassium Iodide

Beta blocker
- (Propranolol, Esmolol)

131I

Diatrizoate, Glucocorticoids

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7
Q

Thioamides

MOA

A
  • Propylthiouracil and Methimazole are referred as goitrogens due to their ability to cause goiter.
  • Both of them block iodination of thyroglobulin and inhibit coupling reaction of DIT with MIT (T3) & DIT joining with another DIT (T4). Hence, formation of T3 and T4 is reduced.
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8
Q

Thioamides PD, PK

A
  • “I” transported into thyroid (Via Na+:I– symporter –NIS)–> thioamides inhibit thyroperoxidase (TPO) –> MIT + DIT ↓(T3), & DIT + DIT ↓(T4)
  • Oral rout of administration.
  • They do not inhibit the preformed T4 / T3; as a result –slow onset of action. Takes 2-3 weeks for full effect
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9
Q

DOC in thyroid storm due to its inhibitory effect on 5’–deiodinase also that result in decrease peripheral conversion from T4 to T3.

A

Thioamide: Propylthiouracil

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10
Q

•Uses of Propylthiouracil:

A
  1. PTU is reserved for patients who are intolerant to methimazole; who are not fit for surgery or 131I (RAI) 2. It is also preferred in thyroid storm due to its ability to inhibit T4 to T3 and 3. PTU used in 1st trimester because of rare teratogenisity with methimazole.
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11
Q

Iodine and Iodide salts:

Wolff-Chaikoff effect.

A

Large doses of iodide inhibit thyroid hormone synthesis (↓organification and release) via brief TPO inhibition.

•Wolff-Chaikoff effect is gone after 10 - 14 days that can result in multinodular goiter, if large doses are continued (Jod-Basedow phenomenon).

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12
Q

Iodine and Iodide salts MOA?

A
  • Iodides decrease vascularity and size of the gland. They are used most often before surgery for easy thyroid excision.
  • They are used in conjunction with PTU, and b- blockers in thyrotoxic crisis.
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13
Q

Thioamides- Adverse reactions

A
  • Thioamides are associated with rash and arthralgia; produce rare agranulocytosis, aplastic anemia, hepatotoxicity, hypoprothrombinemia and vasculitis.
  • Serious AE are much less with methimazole than with PTU; because of this methimazole is more preferred in clinical practice.
  • Methimazole is a teratogen –aplasia cutis congenital
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14
Q

Iodine and Iodide salts
•Preparations are available as:

•Adverse effects:]

A
    1. Lugol’s solution – a mixture of iodine & potassium iodide.
    1. Saturated solution of potassium iodide.

•Adverse effects: chronic iodide intoxication (iodism), anaphylactoid reaction –angioedema, swelling of larynx, eyelids; brassy taste, burning of teeth and gums; enlargement of parotid and maxillary glands.

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15
Q 
Radioactive iodine: 131I
MOA
USE
AE
CI
A
  • Radioactive iodine (131I) is taken up and sequestered by thyroid gland. The intracellular 131I damage the tissue through emission of toxic β-rays, no effect on other tissues.
  • Used in adults with hyperthyroidism, Graves’ disease –that has been refractory to other antithyroid drugs and persistent symptoms even after the subtotal thyroidectomy.
  • It is the only medical therapy produces permanent reduction in thyroid activity.
  • There is no evidence of causing any cancer.
  • The desired effect may not be obtained due to the difficulties to determine the dose. Patients may develop hypothyroidism.
  • contraindicated in pregnant women and nursing mothers.
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16
Q

Beta-blockers

A
  • β-blockers are useful in controlling the nervousness, palpitation, fatigue, weight loss, heat intolerance and tremors associated with hyperthyroidism, short-term management in pregnancy, preoperatively, and thyroid storm. Partial agonists are not used.
  • Propranolol, nonspecific beta blocker prevents conversion of T4 to T3.
  • Esmolol, a short acting beta blocker can be used to control intra-operative thyroid storm.
17
Q

Other antithyroid drugs

A
  • Iodinated Radiocontrast Media, like oral diatrizoate or oral / I.V. iohexol will suppress the conversion of T4 to T3 (5’-deiodinase) in the peripheral tissues, kidney and liver. It is useful in rapidly reducing (it has a fast onset of anti-thyroid action) the T3 concentration in thyrotoxicosis. Also may play a role in the inhibition of hormone release from thyroid gland.
  • Perchlorate, thiocyanate and pertechnetate inhibit iodide concentration in the gland by blocking the transportation. Potential for aplastic anemia.
18
Q

Other antithyroid drugs:
A few drugs may provoke autoimmune or destructive inflammatory thyroiditis, inducing hypothyroidism.
What drug has a similar structure to thyroxine?

A
  1. Amiodarone: has structural similarity with thyroxine.
    (a) Iodine associated hyperthyroidism may occur –can be treated with thiamides.
    (b) Autoimmune mediated inflammatory version treated with steroids.
    (c) Hypothyroidism: treated with levothyroxine
  2. Interferon-α & Interleukin-2
  3. Lithium –> inhibits release of hormones (hypothyroidism) and thyroid enlargement
19
Q

Other antithyroid drugs

Drugs that inhibits conversion of T4 to T3

A

“PAG”

  1. Corticosteroids
  2. Propranolol
  3. Amiodarone
20
Q

Other antithyroid drugs

Goitrogens:

A
  • Cabbage (contain thiocyanate)

* Cassava –contains carbohydrates + thiocyanate

21
Q

Other antithyroid drugs

A
  1. Imatinib, Sunitinib (TKRI–Tyrosine Kinase Receptors decrease)
  2. Aminoglutethimide, sulfonylureas.
22
Q

Aplasia cutis congenita

- teratogenicity caused by?

A

Methimazole

23
Q

•Alternatives to β-blockers in thyroid storm for patients with asthma are

A

CCB, Diltiazem or Verapamil.

24
Q

Thyroid storm management?

A

B-Blockers to manage CVS problems such as tachycardia, hypertension.

Propylthiouracyl, IV sodium Iodine and Glucocorticoids to inhibit peripheral conversion of T4 to T3.

25
Q

Drugs that inhibit conversion of T4-T3

A

Corticosteroids
Propranolol
Amiodarone

26
Q

Thioamides (methimazole and propylthiouracil):
MOA
AE

A

prevent MIT and DIT to form T4 and T3. They cause hepatic damage, agranulocytosis, vasculitis and hypoprothrombinemia.

27
Q

Thyroid storm tx options?

A

β-blockers such as propranolol are used to control tachycardia and other CVS abnormalities. Propranolol is also used to inhibit T3 from T4. Other drugs used are: high doses of iodide and propylthiouracil.

28
Q

Iodides USE?

A

(Lugol’s iodine)inhibits synthesis, release of thyroid hormones and decrease the size and vascularity of the hyperplastic gland

29
Q

Amiodarone USE

A

is an antiarrhythmic agent. Its iodine contents could produce complex effects on thyroid hormones. It also inhibits peripheral conversion of T4 to T3

30
Q

I131 USE?

A

is only medical therapy that produces a permanent reduction in thyroid activity.

Pharm final (19 decks)

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