Chapter 31: Throid/ Antithyroid Drugs

Question 1

Hyperthyroidism

Answer 1

Severe form is called thyrotoxicosis

Question 2

Thyroid stimulating hormone (TSH)

Answer 2

An endogenous hormone secreted by the pituitary gland and controls the release of the thyroid gland hormones necessary for its growth

Question 3

Thyroxine (T4)

Answer 3

Principle thyroid hormone influencing metabolic rate

Question 4

Triiodothyronine (T3)

Answer 4

Secondary thyroid hormone that also affects body metabolism

Question 5

Thyroid gland function

Answer 5

Secretes 3 hormones: T3, T4, and calcitonin

Communicate with parathyroid glands that are made up of cells responsible for maintaining adequate levels of calcium in the extra cellular fluid, primarily by mobilizing calcium from bone

Question 6

Process of producing T3 and T4 in the thyroid gland

Answer 6

Iodide is needed for this and is acquired from the diet

1mg is needed per week and is absorbed from the blood and then sequestered by the thyroid gland where it’s concentrated to 20x it’s blood level

It is also converted to iodine which is combined with tyrosine to make diiodotyrosine causing the formation of thyroxine which has four molecules=T4. Coupling of one diiodotyrosine molecule and and one molecule of monoiodotyrosine= T3.

Biological potency of T3 is about 4x greater than T4.

Question 7

After T3 and T4 are synthesized, they are

Answer 7

Stored in the follicles in the thyroid glands in a complex with thyroglobulin (tyrosine and amino acid protein) called colloid. Then thyroglobulin is broken down to release T3 and T4 into the circulation when stimulated by the thyroid gland.this process is triggered by TSH (or thyrotropin) and released from the anterior pituitary gland when blood levels of T3 and T4 are low

Question 8

Thyroid hormones:

Answer 8

Regulate the nasal metabolic rate and lipid and carb metabolism; are essential for normal growth and development; control the heat regulating system (thermoregulatory center in the brain); and have various effects on the CV, endocrine, and neuromuscular systems

Question 9

Primary hypothyroidism

Answer 9

An abnormality in the thyroid gland itself. Occurs when the thyroid gland is not able to perform one of its functions

Most common type

Question 10

Secondary hypothyroidism

Answer 10

Begins at the level of the pituitary gland and results from reduced secretion of TSH which is needed to trigger T3 and T4 release that are stored in the thyroid gland

Question 11

Tertiary hypothyroidism

Answer 11

Caused by a reduced level of the thyrotropin releasing hormone from the hypothalamus which reduces TSH and thyroid hormone levels

Question 12

Hypothyroidism S/S

Answer 12

Cold intolerance, unintentional weight gain, depression, dry brittle hair and nails, and fatigue

Question 13

Hypothyroidism during youth

Answer 13

Can lead to cretinism (characterized by a low metabolic rate, retarded growth and sexual development, possible mental retardation)

Question 14

Hypothyroidism as an adult

Answer 14

May lead to myxedema (characterized by decreased metabolic rate, involves loss of mental and physical stamina, weight gain, hair loss, firm edema, and yellow fullness of the skin

Question 15

Hypothyroidism May result in

Answer 15

Goiter formation (enlarged thyroid gland from overstimulated TSH levels, TSH levels are overstimulated because there is little to no thyroid hormone in the circulation)

Question 16

Drugs causing hypothyroidism

Answer 16

Amiodarone is the most common

Can also cause hyperthyroidism

Question 17

Hyperthyroidism can be caused by different diseases including

Answer 17

Graves’ (most common), and Plummer’s Disease (also known as toxic nodular disease) which is the least common cause

Question 18

Thyroid storm

Answer 18

Severe and life-threatening exacerbation of the S/S of hyperthyroidism that is usually induced by stress or infection

Question 19

Hyperthyroidism S/S

Answer 19

Diarrhea, flushing, increased appetite, muscle weakness, fatigue, palpitations, irritability, nervousness, sleep disorders, heat intolerance, and altered menstrual flow.

Question 20

Natural Thyroid replacement drugs

Answer 20

Derived from the thyroid glands of animals such as cattle and hogs

Only currently one: thyroid/ thyroid desiccated (refers to the drying process used to prepare the drug)

All natural peeps are standardized for their iodine content

Question 21

Synthetic thyroid replacement drugs

Answer 21

Preparations include T3, T4, and liotrix (combo of T3, T4, in a 1:4 ratio)

Question 22

Thyroid replacements dosing

Answer 22

Determined by the appropriate monitoring of serum TSH and free thyroid hormone levels

Question 23

Thyroid drugs MOA

Answer 23

Cellular level- induce changes in the metabolic rate (rate of protein, carbs, and lipid metabolism), increase O2 consumption, body temp., blood volume, and overall cellular growth and differentiation. Stimulate CV system by increasing the number of myocardial beta-adrenergic receptors increasing the sensitivity of the heart to catecholamines and ultimately increases cardiac output

Also increased renal blood flow and the glomerular filtration rate resulting in a diuretic effect

Question 24

Thyroid preparations indications

Answer 24

Replace what the thyroid gland cannot produce to achieve normal thyroid hormone levels

Can be used to diagnose suspected hyperthyroidism and prevent/treat footers

Replace hormones in patients whose thyroid glands have been surgically removed or destroyed by radioactive iodine in the treatment of thyroid cancer or hyperthyroidism

Hypothyroidism during pregnancy is treated with dose adjustments every 4 weeks to maintain TSH levels at the lower end of the normal range; fetal growth may be retarded if maternal hypothyroidism remains untreated during pregnancy

Question 25

Thyroid preparation contraindications

Answer 25

Drug allergy, recent MI, adrenal insufficiency, and hyperthyroidism

Question 26

Adverse effects of thyroid medications

Answer 26

Usually the result of overdose

Most significant: cardiac dysrhythmias with the risk of life-threatening or fatal irregularities

Other more common, less toxic include:

Tachycardia, palpitations, angina, hypertension
Insomnia, tremors, HA, anxiety
Nausea, diarrhea, cramps
Menstrual irregularities, wt. loss, sweat, fever, heat intolerance

Question 27

Thyroid drug interactions

Answer 27

Phenytoin and Fosphenytoin cause reduced levothyroxine effectiveness

Cholestyramine, antacids, calcium salts, iron, and estrogen cause reduced levothyroxine effectiveness

Warfarin causes increased warfarin effects

May enhance the activity of oral anticoagulants

Chilestyramine binds to thyroid hormone in the GI tract possibly reducing absorption of both drugs

Question 28

Thyroid drugs

Answer 28

Synthetic drugs (levothyroxine and liotrix) are common

T3, T4, cost, duration of effect should be considered before drug therapy initiation

Classified as pregnancy category A drugs

Question 29

Levothyroxine

Answer 29

Most commonly prescribed synthetic thyroid hormone (“drug of choice”)

Chemically pure: 100% T4 making it more predictable than other thyroid preparations; it’s half-life is long enough that it only needed to be administered once a day

Oral (should be taken every morning 30-60 minutes before food; tube feedings can impair absorption) and parenteral forms

DO NOT SWITCH BRANDS: can destabilize course of treatment; monitor thyroid function tests

Dose in micrograms; doses higher than 200 mcg should be questioned in case of a mcg- mg error

IV form (50% of oral dose): remember to dilute FIRST, then the dose is calculated upon the concentration of the reconstituted medication, not the size of the vial.

Question 30

Anti thyroid drugs

Answer 30

Aimed to treat the primary cause of the disease or S/S of the disease

Also known as thioamide derivatives and include methimazole and propylthiouracil (PTU)

Radioactive iodine (destroys the thyroid gland- ablation; commonly used to Tx hyperthyroidism and thyroid cancer) and potassium iodine (prophylaxis for radiation exposure) may also be used to treat hyperthyroidism

Question 31

Antithyroid MOA

Answer 31

Methimazole and PTU inhibit incorporation of iodine molecules into the amino acid tyrosine (process required to make T3 and T4) = these drugs then impede the formation of thyroid hormone

PTU inhibits the conversion of T4 to T3 in the peripheral circulation

Neither drug can inactivate the already existing thyroid hormone

Overall effect: decrease in thyroid hormone levels, normalizing overall metabolic rate

Question 32

Anti thyroid indications

Answer 32

Tx hyperthyroidism and prevent the surge in thyroid hormones that occurs after the surgical treatment of or during radioactive iodine therapy for hyperthyroidism or thyroid cancer

Long term administration (several years) may induce a spontaneous remission (e.g., seen in Graves’ disease)

Surgical resection of the thyroid gland (thyroidectomy) is often used in patients who are intolerant to antithyroid therapy and in pregnant women that antithyroid and radioactive iodine therapy is contraindicated

Question 33

antithyroid Contraindications

Answer 33

Drug allergy, use in pregnancy (category D) although is sometimes necessary

The FDA: PTU is to be used in 1st tri only, and methimazole is used for the remainder (reports of scalp abnormalities in fetus with methimazole use)

Pregnant patient treatment is physician specific

Question 34

Antithyroid Adverse Effects

Answer 34

Most damaging/serious: liver and bone marrow toxicity

More common, less toxic: 
Drowsy, HA, vertigo, paresthesia
N/V, diarrhea, hepatitis, loss of taste
Smoky urine, decreased urine output
Agranulocytosis, leukopenia, thrombocytopenia, hypothrombinemia, lymphadenopathy, bleeding
Rash, pruritis
Myalgia, arthralgia 
Increased blood urea nitrogen and serum creatinine levels
Enlarged thyroid glands, nephritis

Question 35

Antithyroid interactions

Answer 35

Additive leucopenic effects when taken in conjunction with other bone marrow suppressants and an increase in the activity of oral anticoagulants

Question 36

Propylthiouracil drug profile

Answer 36

This is a thioamide antithyroid drug

About 2 weeks of therapy may be necessary before therapeutic effects begin

Only oral 50 mg tabs

Methimazole is the only alternative and is rarely used clinically

Question 37

Thyroid replacement drugs: assessment

Answer 37

Include baseline VS, T3, T4, TSH, and doc any past and present medical problems or concerns

Review baseline VS with attention to Hx of cardiac dysrhythmias because of drug-related effects of cardiac irregularities; these dysrhythmias may be life threatening

Female patients: assess impact of thyroid hormones on the reproductive system

Older adults: may have increased sensitivity to thyroid replacement effects; report palpitations, CP, stumbling, falling, depression, incontinence, sweating, SOB, aggravated heart disease, cold intolerance, wt. gain

Different patients may respond different to the same drug/dose

Question 38

Antithyroid drug assessments

Answer 38

Assess VS and S/S of thyroid crisis or thyroid storm (precipitating causes include stress or infection)

Question 39

Levothyroxine pharmacokinetics

Answer 39

Onset of action: 3-5 days

Peak plasma concentrations: within 24 hours

Half life: 6-10 days

Duration of action: 24 hours

Prolonged half life= increased risk for toxicity (wt. loss, tachycardia, nervousness, tremors, hypertension, HA, insomnia, menstrual irregularities, and cardiac irregularities or palpitations.

Highly protein bound (similar to a sustained release drug)= remains in body longer, increased risk for interactions with other protein binding drugs and increase the potential for toxicity

Question 40

Thyroid replacement drug implementations

Answer 40

Given at the same time every day to help maintain consistent blood levels of the drug

Best to take once daily as prescribed

Take in am on empty stomach about 39 minutes before breakfast

Taking in afternoon/evening will lead to sleepiness

Avoid taking OTC antacids, iodine, vitamins, or supplements containing iron/ calcium within a 4 hour time frame

Iodized salt and iodine rich foods (soybeans, tofu, seafood, some breads) must be avoided

Avoid interchanging replacement brands because of possible differences in their bio equivalence from various manufacturers

May crush if needed

For radioactive iodine isotope studies (thyroid uptake and scan) the thyroid drug is usually discontinued about 4 weeks before the test (only as prescribed)

Older adults: may require alteration of the dose amount with a decrease of up to 25% for patients 69 years and older

Question 41

Antithyroid implementations

Answer 41

Take with meals to decrease GI upset

Report fever, sore throat, mouth sores or ulcers, skin eruptions, unusual bruising or bleeds (may indicate liver/bone toxicity with possible leukopenia)

Monitor liver function tests and CBC counts

Avoid iodized salts or shellfish because of their potential for altering the drugs effectiveness

Advise patients to be aware of S/S of hypothyroidism: unexplained wt. gain, loss of mental and physical stamina, hair loss, firm edema, and yellow fullness of the skin (Indicative of myxedema or a decrease in metabolic rate)

Question 42

Thyroid replacement drugs evaluations

Answer 42

Decrease is S/S of hypothyroidism

Improved energy levels, mental stamina, and physical stamina

Clues of possible inadequate doses: return of hypothyroidism S/S

Question 43

Antithyroid medications evaluations

Answer 43

Return to normal status with little or no evidence of hyperthyroid

Clues of inadequate dosing: continued hyperthyroidism S/S

Question 44

Thyroid replacement patient teachings

Answer 44

Best taken 1/2-1 hour before breakfast on an empty stomach to enhance their absorption orally and to maintain hormone levels

Sleepiness can be prevented by taking Ned in morning

Not to be abruptly discontinued

Follow ups are significant

Brands can not be interchanged

Provide S/S to look for and to report

Take with 6-8 oz of water

Report CP, wt. loss, palpitations, tremors, sweat, nervousness, SOB, insomnia because these may indicate toxicity

Encourage journal use

May take weeks to see therapeutic effects

Keep tablets protected from the light

Question 45

Antithyroid patient teachings

Answer 45

Better tolerated with meals or snack

Never to be withdrawn abruptly

Avoid eating foods high in iodine such as tofu, and other soy products, turnips, seafood, iodized salts, and some breads because they may interfere with the effectiveness of the antithyroid drugs