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Pharmacology > thyriod pharmacology > Flashcards

thyriod pharmacology Flashcards

1
Q

whats The free (unbound) hormone small percentage of T4 and T3 of the total hormone in plasma?

A

~0.03% of T4 and ~ 0.3% of T3

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2
Q

list the steps invoved in Synthesis, storage, release and interconversion of thyroid hormones

A

Involves the following steps:

1) Uptake of plasma iodide
2) Oxidation and iodination
3) Coupling
4) Secretion of thyroid hormone
5) Peripheral conversion of T4 to T3

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3
Q

Iodide transport is inhibited by a number of ions, such as

A

thiocyanate and perchlorate

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4
Q

The oxidation and iodination is accomplished by what enzyme

A

thyroid peroxidase

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5
Q

what enzyme selectively cleave thyroglobulin, yielding hormone-containing intermediates

A

Lysisomal thiol endopeptidases selectively cleave thyroglobulin

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6
Q

the hormone-containing intermediates that subsequently are processed by ?

A

exopeptidases

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7
Q

what accounts for about 80% of circulating T3 ?

A

metabolism of T4 by 5′, or outer ring, deiodination in the peripheral tissues

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8
Q

D1 is expressed primarily ? and inhitited by?

A

liver and kidney and also in the thyroid and pituitary and inhibited by the antithyroid drug propylthiouracil.

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9
Q

what enzyme is unaffected by propylthiouracil

A

activity of D2 is unaffected by propylthiouracil

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10
Q

what does D3 do

A

catalyzes T3 metabolism, resulting in the formation of rT3 (metabolically inactive)

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11
Q

Functions of Thyroid Hormones

A

1) Growth and development; Normal growth and development of organism, especially the brain

2)Metabolism; i)Lipid: Induce lipolysis, ↑ free plasma fatty acid and all phases of cholesterol metabolism enhanced.
ii)Carbohydrate: Stimulation of carbohydrate metabolism -glycogenolysis and gluconeogenesis.
iii)Protein: Certain protein synthesis increased but overall catabolic action is that of negative nitrogen balance.

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12
Q

T4 versus T3 (4)

A

T4 is less active and a precursor of T3 - the major mediator of physiological effects

T3 is 5 times more potent than T4

T4 is 15 times more tightly bound to plasma protein than T3

T3 acts faster and its effect peaks in 1- 2days, while T4 effect peaks in 6-8 days

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13
Q

Thyroid Hypofunction whats its severe, is the most common and its chronic autoimmune

A

myxedema resulting from iodine deficiency,while In non-endemic areas where iodine is sufficient, chronic autoimmune thyroiditis (Hashimoto thyroiditis) accounts for most cases.

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14
Q

Drugs that can cause hypothyroidism include

A

iodides, lithium and amiodarone

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15
Q

Thyroid Hyperfunction; whats Thyrotoxicosis

A

Thyrotoxicosis is a condition caused by elevated concentrations of circulating free thyroid hormones

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16
Q

most common cause of high thyrotoxicosis

A

Graves disease is the most common cause of high thyrotoxicosis. is an autoimmune disorder characterized by increased thyroid hormone production, diffuse goiter, and IgG antibodies that bind to and activate the TSH receptor

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17
Q

Indications for Thyroid Hormone replacement therapy (7)

A

Cretinism:
Adult hypothyroidism
Myxoedema coma
Nontoxic goiter
Thyroid nodule
Papillary carcinoma of thyroid

Other uses: T4 used for treatment of refractory anemia, mental depression, menstrual disorder or infertility

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18
Q

Other causes of hyperthyroidism : (3)

A

Toxic uninodular or multinodular goiter (overproduction of thyroid hormone independent of TSH),
destructive thyroiditides
excessive doses of thyroid hormone

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19
Q

Myxoedema coma is precipitated by?

A

precipitated by pulmonary infections, CVA and CHF

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20
Q

list the Thyroid Hormone Preparations (3)

A

Levothyroxine
Liothyronine
Other preparations; A mixture of levothyroxine and T3 around 4:1 by weight and desiccated thyroid preparations (from pig) with a similar T4:T3 ratio also are available

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21
Q

description of Thyroid levothyroxine

A

Levothyroxine sodium is available in tablets and liquid-filled capsules for oral administration and as a lyophilized powder for injection

22
Q

MOA for Levothyroxine

A

replacing deficient thyriod hormone

23
Q

pharmacokinetics of levothyroxine

A

Absorption of levothyroxine occurs in the stomach and small intestine and is incomplete (~80% of the tablet dose is absorbed)

24
Q

drug interactions of thyroid preparations

A

Drugs that induce the cytochrome P450 enzymes, such as phenytoin,
rifampin, and phenobarbital, accelerate metabolism of the thyroid hormones and may decrease the effectiveness

25
Q

why is Liothyronine less desirable for chronic replacement therapy (3)

A

due to the requirement for more-frequent dosing (plasma t1/2 is 18–24 h),
higher cost, and
transient elevations of serum T3 concentrations above the normal range

26
Q

Adverse Effects of Thyroid Hormones

A

similar to the consequences of hyperthyroidism in general

increase the risk of atrial fibrillation, especially in the elderly
Increased risk of osteoporosis, especially in postmenopausal women

27
Q

list the classes of drugs used to treat hyperthyroidism, they are AGENTS THAT DISRUPT THYROIDHORMONE SYNTHESIS, RELEASE, AND METABOLISM

A

Antithyroid drugs
Ionic inhibitors
High concentrations of iodine,
Radioactive iodine,

28
Q

examples of Antithyroid Drugs

A

propylthiouracil (prototype)
carbimazole
methimazole

29
Q

Carbimazole is a carbethoxy derivative of ?

A

Carbimazole is a carbethoxy derivative of methimazole and its antithyroid action is due to its conversion to methimazole after absorption

30
Q

MOA of Propylthiouracil (Anti-thyroid drugs) (4)

A

interferes with the iodination process of thyroid synthesis
They also inhibit the coupling process of thyroid synthesis
also inhibit the peroxidase enzyme

propylthiouracil partially inhibits the peripheral deiodination of T4 to T3. Methimazole does not have this effect

31
Q

what’s the preferred drug choice in the treatment of severe hyperthyroid states or of thyroid storm

A

propylthiouracil

32
Q

PK of Propylthiouracil (Anti-thyroid drugs)

A

Absorption of effective amounts of propylthiouracil occurs within 20–30 min of an oral dose;
The drugs are concentrated in the thyroid,
Drugs and metabolites appear largely in the urine

33
Q

still pk; how long is the t1/2 of propylthiouracil in plasma and that of methimazole

A

the duration of action is brief,
The t1/2 of propylthiouracil in plasma is about 75 min; that of methimazole is 4–6 h

34
Q

Indications / Therapeutic Uses of Anti-thyroid drugs

A

are used in the treatment of hyperthyroidism in the following ways:

As definitive treatment, to control the disorder in anticipation of a spontaneous remission in Graves disease
In conjunction with radioactive iodine, to hasten recovery while awaiting the effects of radiation
To control the disorder in preparation for surgical treatment

35
Q

whats is the drug of choice for Graves disease and WHY (3)?

A

Methimazole, cuz
it is effective when given as a single daily dose,
has improved adherence, and
is less toxic than propylthiouracil

36
Q

ADRs of Propylthiouracil (Anti-thyroid drugs ) minor(7) and major (6)

A

Minor
GIT intolerance, rashes, urticaria, fever, anorexia, nausea, taste and smell abnormalities

Major
Agranulocytosis, Thrombocytopenia, Acute hepatic necrosis, Cholestatic hepatitis, Vasculitis, Lupus-like syndrome

37
Q

Monitoring of ADR in Anti-thyroid drugs (4 steps)

A

screen for Blood disorders- first two months of treatment
Routine leucocytes counts
Patient advised to stop drugs if symptoms of sore throat, fever, mouth ulcers develop and have leucocytes count performed
If agranulocytosis develops – withdraw drug

38
Q

The antithyroid drugs belong to the family of ?

A

thioamides

39
Q

agents that disrupt IODIDE UPTAKE

A

PERCHOLATE, THIOCYANATE, NITRATE, FLUOROBORATE

40
Q

agents that disrupt ORGANIFICATION OF IODINE

A

thioamides, thiocyanate, sulfonamides

41
Q

agents that disrupt COUPLING REACTION

A

thioamides, sulfonamides

42
Q

agents that disrupt HORMONE RELEASE

A

lithium salts, iodide

42
Q

agents that disrupt PERIPHERAL IODOTHYRONINE DEIODINATION

A

propylthiouracil, amiodarone, oral cholescystographic agents

43
Q

agents that disrupt ACCELERATED HEPATIC METABOLISM

A

phenytoin, phenobarbital, rifampicin, carbamazepine

44
Q

Iodine use in hyperthyroidism and In euthyroid state

A

In hyperthyroidism - moderate excess of iodine ↑ synthesis, substantial excess - inhibits hormone release, promote storage, gland firmness, ↓ vascularity

In euthyroid state - excess iodine causes goiter, and hard nodules become hypothyroid

45
Q

Radioiodine, MOA use and contraindications

A

Swallowed I131 trapped and concentrated in thyroid follicles
MOA; which damages the thyroid gland with ionizing radiation
Used in diffuse toxic goiter (Thyrotoxicosis / Grave’s disease), toxic nodular goiter, thyroid carcinoma

Beneficial effects seen within one month

Contraindications - pregnancy, lactation, children

46
Q

Role of beta-adrenergic blockers in Hyperthyroidism

A

There is increased tissue sensitivity to catecholamine in hyperthyroidism

Provides quick relief of adrenergic symptoms - palpitation, tremor, nervousness, myopathy and sweating

Not used as sole therapy and does not alter the course of the disease and thyroid function test

47
Q

what is Thyroid storm or crises

A

A sudden aggravation of symptoms of thyrotoxicosis, characterized by fever, sweating, tachycardia, extreme nervous excitability, and pulmonary edema. It is a life-threatening emergency

48
Q

Thyroid storm or crises is precipitated by?

A

by infection, trauma, toxemia of pregnancy

49
Q

Thyroid storm or crises is treated by?

A

hint;PPS
propranolol, propylthiouracil and steroids (hydrocortisone/prednisolone)

Pharmacology (11 decks)

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