L34- Thyroid and Antithyroid Drugs (intro + hypothyroid) Flashcards Preview

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Flashcards in L34- Thyroid and Antithyroid Drugs (intro + hypothyroid) Deck (18)
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briefly review TH biosynthesis

1) Iodide ion uptake (I-)
2) oxidation, I- --> I2 (iodine, in colloid)
3) iodination of tyrosyl groups on Thyroglobulin
4) iodotyrosine residue coupling --> THs
5) TH resorption from colloid
6) thyroglobulin proteolysis --> thyroxine and triiodothyronine in blood


(T3/T4) is more rapid/potent because of (2) and (3)

1- T3
2- T3 bind plasma proteins less tightly
3- T3 bind TH nuclear receptors more tightly


list methods of TH metabolism

-deiodoination (most important)


(1) is the most important method of TH metabolism. (1) process usually occurs in (2) manner. Inhibition of (3) will result in (4).

1- deiodonation

T4 --> T3, more potent than T4
T4 --> rT3 (reverse), inactive

3- 5'-deiodinase

4- low T3 in serum


5'-deiodinase enzymes are inhibited by.....

-drugs: propylthiouracul, propanlol, corticosteroids, amiodarone

-severe illness / starvation

-iodinated compounds --> radiographic agents iopnanoic acid, ipodate


describe the alternate method of TH metabolism

T3/T4 --> liver --> sulfation, glucuronidation --> enters bile --> intestine --> hydrolyzed --> reabsorbed or excreted in stool


describe how metabolism of TH can be targeted

Deiodinase and UDP glucuronosyltransferase enzymes are inducible

drugs that are enzyme inducers --> inc T3/T4 metabolism (if on replacement therapy, higher T4 dose is required)


describe hypothyroidism thyroid preparation classification

-levothyroxine, T4
-liothyronine, T3
-liotrix (T4/T3 mix)

Natural: via animal, desiccated thyroid


Synthetic TH:
-(Y/N) protein Ag
-(uniform/variable) hormone concentrations
-(easy/difficult) lab monitoring
-(high/low) cost

1- No
2- stable
3- uniform
4- easy
5- high cost
6- preferred


Natural TH:
-(Y/N) protein Ag
-(uniform/variable) hormone concentrations
-(easy/difficult) lab monitoring
-(high/low) cost

1- Yes
2- unstable
3- variable
4- difficult
5- low cost
6- not preferred


Levothyroxine (vs liothyronine):
-(more/less) potent
-(long/short) 1/2 life
-(3) dosing frequency
-(easy/difficult) lab monitorig
-(higher/lower) cardiotoxicity risk

1- less
2- longer
3- po qd
4- easy
5- lower
6- preferred


Liothyronine (vs levothyroxine):
-(more/less) potent
-(long/short) 1/2 life
-(3) dosing frequency
-(easy/difficult) lab monitorig
-(higher/lower) cardiotoxicity risk

1- more
2- shorter
3- multiple times daily
4- difficult
5- higher
7- not preferred


(T/F) Liotrix is the preferred option for thyroid hormone replacement therapy

F- liotrix (T3/T4) is equally or less efficacious as levothyroxine (T4), but more expensive


Thyroid replacement therapy AEs


-higher risk of AFib, osteoporosis


(1) is a severe complication of long-standing hypothyroidism, with (2) as the cardinal features. (1) is treated / managed by (3).

1- Myxedema coma

2- hypothermia, respiratory depression, dec consciousness

3- IV levothyroxine (maybe liothyronine until Pt is stable and conscious) + supportive measures


_____ is the drug of choice for hypothyroidism in pregnancy (and its importance)

-adequate (maybe increasing) dose of levothyroixine

Fetal brain development depends on maternal thyroxine


why is a higher dose of levothyroxine required in pregnancy

1) inc serum [thyroxine binding globulin / TBG] induced by estrogen

2) placental expression of 5'-deiodinase (D3)

3) small amount of transplacental passage of levothyroxine to fetus


what is the important factor in treating congenital hypothyroidism

start w/in 1st two weeks of life --> normal physical and mental development

-development may be affected if started later