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RRPA Pharmacology III > Thyroid therapy- hypothyroidism only (Exam 1) > Flashcards

Thyroid therapy- hypothyroidism only (Exam 1) Flashcards

1
Q

Management of hypofunction for thyroid is what?

A

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

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2
Q

Management of hyperfunction of thyroid is what?

A

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

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3
Q

The ______ of levothyroxine infroms its pharmacotheraputic use

A

physiology

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4
Q

What three things inhibit the release of TSH?

A
  1. Somatostatin
  2. Dopamine
  3. Glucocorticoids
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5
Q

What stimulates the release of TSH?

A

TRH

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6
Q

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

A

Uptake of Iodide ion

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7
Q

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

A
  1. SCN
  2. CLO4
  3. Iodide itself when given at high concentrations >6mg
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8
Q

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

A

hypothyroidism

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9
Q

How does the TSH Thyrotropin work?

A

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

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10
Q

When would thyrotropin be used?

A
  • in the treatment of metastatic thyroid carcinoma

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

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11
Q

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

A

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

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12
Q

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

A

65-85%

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13
Q

What is the bioavailability of T3 in the ileum-colon

A

95%

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14
Q

Treatment of hypothyroidism?

A

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

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15
Q

Is the dose of levothyroxine greater for infants or adults?

A

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

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16
Q

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

A. Infants
B. Adults
C. Elderly

A

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

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17
Q

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

A

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

also because of increased placental metabolism of T3-T4

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18
Q

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

A

an underlying cardiac disease

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19
Q

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

A
  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
20
Q

True or false: Levothyroxine has a large therapeutic index?

A

false it has a narrow one

21
Q

How should levothyroxine be taken?

A

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

22
Q

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

A

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

23
Q

What drugs impair levothyroxine absorption?

A
  1. metal ions (antacids-Ca++-Fe++)
  2. ciprofloxacin
  3. bile acid sequestrants
  4. raloxifene
  5. sucralfate
  6. dietary fiber
  7. soy
24
Q

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

A

only the unbound form.

25
Q

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

A

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

26
Q

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

A
  1. Estrogens
  2. SERMs
  3. Tamoxifen
27
Q

What drugs cause a decrease in binding of thyroid hormone?

A
  1. Salicylates

2. Antiseizure meds (phenytoin, carbamazepine)

28
Q

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

A

True

29
Q

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

A
  1. peripheral tissues

2. Liver

30
Q

T3 in brain and pituitary derived by _______ deiodination?

A

intracellular

31
Q

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

A
  1. Glucocorticoids
  2. Beta-Blockers
  3. Amiodarone
  4. PTU (propylthiouracil)
32
Q

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

A
  1. Increased

2. Decreased

33
Q

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

A

CYP450 our good friend

34
Q

What is the half life of T4 and T3?

A

T4 is 7 days

T3 is 1 day

35
Q

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

A

Degree of protein binding.

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

36
Q

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

A

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

37
Q

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

A
  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
38
Q

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

A

synthetic T4

39
Q

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

A

6 weeks after

40
Q

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

A
  • within 2-3 weeks

- requires 6-8 weeks of maintenance dose to approach steady-state plasma levels

41
Q

Why is Liothyronine not recommended for routine replacement?

A

this is because it has a short half life which means great Cp fluctuations between doses

It also require alot of green backs

42
Q

If someone has a cardiac disease should you use Liothyronine?

A

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

43
Q

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

A

T3 for sure

44
Q

Liotrix what you need to know.

A

Rarely required, not recommended

More expensive

combined therapy may cause increased incidence of low TSH concentrations and increased markers of bone turnover

45
Q

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

A

nope

46
Q

________ is dessicated porcine thyroid extract containing T3 and T4

A

Thyroid USP

47
Q

Disadvantages of Thyroid USP?

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

RRPA Pharmacology III (9 decks)

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