Thyroid therapy- hypothyroidism only (Exam 1)

Question 1

Management of hypofunction for thyroid is what?

Answer 1

Hormone replacement (physiologic) therapy for deficiency sates (Hypothyroidism)

Question 2

Management of hyperfunction of thyroid is what?

Answer 2

Suppression of hormone synthesis or effect (nonhormonal agents) —> hyperthyroidism

Question 3

The ______ of levothyroxine infroms its pharmacotheraputic use

Answer 3

physiology

Question 4

What three things inhibit the release of TSH?

Answer 4

1. Somatostatin
2. Dopamine
3. Glucocorticoids

Question 5

What stimulates the release of TSH?

Answer 5

TRH

Question 6

What is the major regulated step in the biosynthesis of thyroid hormones?

Answer 6

Uptake of Iodide ion

Question 7

What can be used to block the uptake of iodide ion?

Answer 7

1. SCN
2. CLO4
3. Iodide itself when given at high concentrations >6mg

Question 8

What type of symptoms can lithium produce when used as anti-manic therapy?

Answer 8

hypothyroidism

Question 9

How does the TSH Thyrotropin work?

Answer 9

Stimulates cAMP production which results in increased uptake of iodine and production of thyroid hormones. (lithium blocks this action of TSH)

Question 10

When would thyrotropin be used?

Answer 10

• in the treatment of metastatic thyroid carcinoma

- it will increase the uptake of radioactive iodine thus destroying the thyroid

Question 11

What effect does thyroid hyperactivity have on sympathetic nervous system and cardiovascular?

Answer 11

increased SNS activity and increased number of beta-adrenergic receptors and adenylyl cyclase activity on the heart

Question 12

What is the bioavailability of T4 in the ileum-colon?

Answer 12

65-85%

Question 13

What is the bioavailability of T3 in the ileum-colon

Answer 13

95%

Question 14

Treatment of hypothyroidism?

Answer 14

Replacement therapy is appropriate; use of levothyroxine (T4) most satisfactory. For adults, generally start with 50-100 mcg, working up to 1.6-1.8 mcg/kg/day

Question 15

Is the dose of levothyroxine greater for infants or adults?

Answer 15

infants, they can go up to 15mcg/kg and should be monitored for development

Question 16

Out of the three options below, who would get the lowest dose of levothyroxine (T4)

A. Infants
B. Adults
C. Elderly

Answer 16

The elderly, they can go as low as 0.5mcg/kg

Question 17

Why would pregnancy require an increased dose of to treat hypothyroidism?

Answer 17

because of increased levels of TBG (via increased estrogen). This decreases free T3-T4

also because of increased placental metabolism of T3-T4

Question 18

What type of condition would make you stop and use caution when prescribing something to increase thyroid function?

Answer 18

an underlying cardiac disease

Question 19

is Myxedema coma a medical emergency? How do you treat it?

Answer 19

1. Yes
2. Large doses of T4 required with IV loading dose of T4 followed by daily IV dosing (can use T4 and T3 together or just T3 alone)
3. Hydrocortisone may be required to prevent adrenal crisis because thyroid hormone may increase its metabolism

Question 20

True or false: Levothyroxine has a large therapeutic index?

Answer 20

false it has a narrow one

Question 21

How should levothyroxine be taken?

Answer 21

Levothyroxine should be taken alone on an empty stomach, with a full glass of water, at least 30 minutes before breakfast

Question 22

How does one manage avoiding absorption impairment of levothyroxine caused by other drugs?

Answer 22

Managed by spacing levothyroxine dose 2 hours before or 4-6 hours after interacting drug.

Question 23

What drugs impair levothyroxine absorption?

Answer 23

1. metal ions (antacids-Ca++-Fe++)
2. ciprofloxacin
3. bile acid sequestrants
4. raloxifene
5. sucralfate
6. dietary fiber
7. soy

Question 24

Which form of the thyroid hormone has metabolic activity? Bound or unbound?

Answer 24

only the unbound form.

Question 25

Changes with what will have major effects on total thyroid serum hormone levels?

Answer 25

Changes in either the concentrations of binding proteins OR binding affinity of hormone for protein

Question 26

What drugs cause an increase in binding of the thyroid protein?

Answer 26

1. Estrogens 2. SERMs 3. Tamoxifen

Question 27

What drugs cause a decrease in binding of thyroid hormone?

Answer 27

1. Salicylates | 2. Antiseizure meds (phenytoin, carbamazepine)

Question 28

True or false: laboratory tests that measure total hormone levels can be misleading?

Answer 28

True

Question 29

T3 80% utilized by _________ ________ is derived from T4 deiodination in the _______

Answer 29

1. peripheral tissues | 2. Liver

Question 30

T3 in brain and pituitary derived by _______ deiodination?

Answer 30

intracellular

Question 31

T4 is converted into T3 the active hormone by an activating enzyme. Drugs can INHIBIT this enzyme. Which ones do this?

Answer 31

1. Glucocorticoids 2. Beta-Blockers 3. Amiodarone 4. PTU (propylthiouracil)

Question 32

Metabolic clearance rates may be ______ in hyperthyroidism and ________ by hypothyroidism?

Answer 32

1. Increased | 2. Decreased

Question 33

Metabolic clearance rates my also be increased with _______ enzyme induction (carbamazepine, digoxin, phenytoin, rifampin)

Answer 33

CYP450 our good friend

Question 34

What is the half life of T4 and T3?

Answer 34

T4 is 7 days | T3 is 1 day

Question 35

What is the major factor for the difference in the half lives?

Answer 35

Degree of protein binding. Remeber free T4 is .04% where as free T3 is .4% alot less bound to proteins

Question 36

Because T4 has a long half live it allows for what kind of dosing?

Answer 36

once daily dosing and can miss a dose or so and still maintain therapeutic levels

Question 37

For the management of hypothyroidism there are four drug options. what are they?

Answer 37

1. Levothyroxine (synthetic T4) 2. Liothyronine aka cytomel (synthetic T3) 3. Liotrix aka thyrolar (4:1 mixture of T4 and T3) 4. Thyroid USP aka armour thyroid (variable T4/T3 ratio

Question 38

Between synthetic T3 and T4 which one is the preferred preparation of choice for thyroid replacement?

Answer 38

synthetic T4

Question 39

When should a thyroid function test be checked after a change in levo product formulation?

Answer 39

6 weeks after

Question 40

When would one expect to se resolution of symptoms from hypothyroidism if being treated with levo?

Answer 40

- within 2-3 weeks | - requires 6-8 weeks of maintenance dose to approach steady-state plasma levels

Question 41

Why is Liothyronine not recommended for routine replacement?

Answer 41

this is because it has a short half life which means great Cp fluctuations between doses It also require alot of green backs

Question 42

If someone has a cardiac disease should you use Liothyronine?

Answer 42

No because it is synthetic T3 which puts it at a greater risk of cardiotoxicity

Question 43

Which has a greater affinity for thyroid hormone receptors T4 or T3

Answer 43

T3 for sure

Question 44

Liotrix what you need to know.

Answer 44

Rarely required, not recommended More expensive combined therapy may cause increased incidence of low TSH concentrations and increased markers of bone turnover

Question 45

Currently is Thyroid USP (Armour Thyroid) recommended for use in hypothyroidism?

Answer 45

nope

Question 46

________ is dessicated porcine thyroid extract containing T3 and T4

Answer 46

Thyroid USP

Question 47

Disadvantages of Thyroid USP?

Answer 47

1. Variable T4/T3 ratio and content that may produce unexpected toxicities 2. Protein antigenicity 3. Product instability