Thyroid & Antithyroid drugs Flashcards by Erik Mai

How is iodine synthesized into thyroid hormones?

iodine is covalently bound to tyrosine residues in the thyroglobulin molecules via thyroperoxidase.

MIT + DIT = triiodothyronine (T3)
DIT + DIT = thyroxine (T4)

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what is reversible triiodothyronine (rT3)?

isomer of T3.
derived from T4 through deiodinase.
blocks action of T3.

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what are the synthesis and secretion steps of thyroid hormones?

uptake of iodine
synthesis of thyroglobulin from A.A
iodination
condensation

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What are the physiological effects of thyroxine?

increase BMR via Na/K ATPase
- increase RR
- increase temperature
- increase O2
potentiates the effects of catecholamines
- increase CO
- enhances HR
promotes CNS development.

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PK of thyroid T3 and T4?

T3 formed from deiodination (5’-deiodinase) of T4 in the peripheral tissues, liver, kidney.
Thyroxin-binding protein transport T3 and T4
T3 has greater affinity than T4

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Physiological controls of thyroid gland?

the pituitary gland is regulated by hypothalamus (TRH)
– activated by cold, acute psychosis, circadian and pulsatile rhythm.
– inhibited by severe stress.
thyroid gland is under control of the pituitary gland (TSH)
negative feedback is from T3 and T4.

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MOA of thyroid hormones?

signaling mechanism is via TRH-IP3 mediated, TSH-cAMP mediated, T3 & T4 binds with receptor in the nucleus.
mechanism: binds c intracellular receptors that control gene expression c RNA formation and protein synthesis.
proteins synthesized depends on tissues involved

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What are some thyroid preps?

Levothyroxine (T4) - longer t1/2

Liothyronine (T3) - short t1/2

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Levothyroxine
Liothyronine

uses?

cretinism (thyroid hormone syn defect)
adult hypothyroidism (myxedema)

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Levothyroxine
Liothyronine

A.E?

tremors
tachycardia
arrythmias
heat intolerance

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what are some P450 inductions that can increase the metabolism of T3 and T4?

rifampin
phenobarbital
phenytoin

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primary hypothyroidism?

Hashimoto's thyroiditis - anti-TPO
radiation exposure 
"I" deficiency
excision
drugs - lithium, amiodarone

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secondary hypothyroidism?

pituitary pathology.

radiation, surgery or tumor
decrease TSH

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Tertiary hypothyroidism?

hypothalamus pathology.

decreased TRH

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hypothyroidism lab diagnosis?

elevated TSH
decreased total T4
decreased free T4
decreased T3

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clinical fts of hypothyroidism?

cold tolerance
constipation
poor memory
hair loss - queen anne's sign (thinning of hair lateral third of eye brow)
carpal tunnel syndrome
hoarse voice
puffy face
bradycardia
delayed DTRs

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describe cretinism…

fts: mentally retarded, short stature child c protruding umbilicus, pot belly, pale& puffy face and tongue is protruding
causes: lack of dietary iodine; defect in T4 syn or devel failure of thyroid

screen and tx pts, including congenital defect, c T4 (c/in -2 wks of life)

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hyperthyroidism lab diagnosis?

decreased TSH
elevated T4
elevated free T4
elevated T3

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hyperthyroidism causes?

Graves' disease
toxic multinodular goiter
toxic adenoma
molar pregnancy
postpartum thyrotoxicosis
postviral thyroiditis

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PE/History of Hyperthyroidism?

weight loss
heat tolerance
nervousness
palpitation
bowel frequency
insomnia
abnl menses

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what are fts of Graves?

ophthalmopathy

pertibial myxedema

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what are two thioamides to treat hyperthyroidism?

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propythiouracil

methimazole

what are two iodine & iodide salts to treat hyperthyroidism?

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lugol sln

potassium iodide

what is a beta blocker used in hyperthyroidism?

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propanolol

propythiouracil methimazole MOA?

block iodination of thyroglobulin inhibit coupling rxn of DIT c MIT & DIT inhibit thyroperoxidase

Which thioamides is preferred in thyroid storm and why?

propythiouracil d/t its inhibitory effect on 5-deiodinase that result in decrease peripheral conversion from T4 and T3.

what are the two uses for propythiouracil?

1. reserved for pts who are intolerant to methimazole | 2. preferred in thyroid storm.

propythiouracil methimazole A.E?

propythiouracil: rash, arthralgia rare - agranulocytosis, aplastic anemia, hepatotoxicity, vasculitis methimazole: less A.E possible teratogenic.

What is the Wolff-Chaikoff effect?

give large doses of iodide inhibit thyroid synthesis.

What is the Jod-Basedow phenomenon?

multinodular goiter devel after Wolff-Chaikoff effect is lost after 10-14 days.

lugol sln potassium iodide actions?

decrease vascularity and size of the thyroid gland.

lugol sln potassium iodide uses?

before surgery for easy thyroid excision. | conjunction c PTU, and beta blockers in thyrotoxic crisis

lugol sln potassium iodide preparations?

Lugol: a mixture of iodine and postassium iodide. KI: saturated sln.

lugol sln potassium iodide A.E?

chronic iodide intoxication (iodism) anaphylactoid rxn - angioedema, swelling of larynx, eyelids brassy taste burning of teeth and gums enlargement of parotid and maxillary glands

Radioactive iodine 131(I) MOA?

taken up and sequestered by thyroid gland -> damage the tissue through emission of toxic beta rays, no effect on other tissues.

Radioactive iodine 131(I) uses?

hyperthyroidism Graves' disease refractory to other antithyroid drugs and persistent sx's even after a subtotal thyroidectomy

Radioactive iodine 131(I) A.E?

hypothyroidism

Radioactive iodine 131(I) contraindications?

pregnant women and nursing mothers.

propanolol MOA?

prevents conversion of T4 and T3

nadolol or atenolol uses?

control tachycardias, htn, a fib during thyroid storm

esmolol use?

control intra-operative thyroid storm

diltiazem use?

Ca channel blocker - use in thyroid storm for pts c asthma

what is thyroid storm?

assoc c extreme effects of hyperthyroidism | - caused by illness, surgery, and other stresses

what are the two iodinated radiocontrast media?

diatrizoate | iohexol

diatrizoate iohexol MOA?

suppress conversion of T4 and T3 in peripheral tissues, kidney, and liver.

diatrizoate iohexol uses?

rapidly reduce T3 conc in thyrotoxicosis

Perchlorate thiocyanate pertechnetate MOA?

inhibit iodide conc in the gland by blocking transportation

Perchlorate thiocyanate pertechnetate A.E?

aplastic anemia

what are drugs that can induce hypothyroidism?

amiodarone interferon alpha & IL-2 lithium

amiodarone fts?

structurally similar to thyroxine

amiodarone A.E and tx?

iodine assoc hyperthyroidism - tx c thiamides autoimmune mediated infl - tx c steroids hypothyroidism - tx c levothyroxine

Lithium MOA?

inhibits release of hormones (hypothyroidism) and thyroid enlargement.

what are the two goitrogens?

cabbage | cassava

what is the function of the thyroid gland?

- take up iodine and convert it into thyroid hormones.

Thyroid & Antithyroid drugs Flashcards

(54 cards)