Thyroid Agents

Thyroid Agents Nursing Pharmacology and Study Guide

Thyroid gland is located in the middle of the neck and surrounds the trachea like a shield. It produces two hormones: thyroid hormone and calcitonin. The thyroid gland uses iodine to produce thyroid hormones that regulate body metabolism. Thyroid agents either replace or remove hormones to prevent deficiency and excess. Thyroid agents include thyroid hormones (T3, T4, TSH)and antithyroid drugs (further classified as thioamides and iodine solution).

Table of Common Drugs and Generic Names


Here is a table of commonly encountered thyroid agents, their generic names, and brand names:

Classification Generic Name Brand Name
Thyroid Agents
Thyroid Hormones levothyroxine Synthroid, Levoxyl
liothyronine Cytomel, Triostat
liotrix Thyrolar
thyroid dessicated Amour Thyroid
Antithyroid Agents
Thioamides methimazole Tapazole
propylthiouracil (PTU)
Iodine solutions sodium iodide I131
strong iodine solution, potassium iodide Thyro-Block

Disease Spotlight: Thyroid Dysfunction


  • Thyroid dysfunction involves either under activity (hypothyroidism) or overactivity (hyperthyroidism). This can affect any age group.
  • Hypothyroidism is a lack of sufficient levels of thyroid hormones to maintain a normal metabolism. This is the most common type of thyroid dysfunction and is common among older women and men. Symptoms include obesity and fatigue, among others. Severe adult hypothyroidism is called
  • Cretinism is a condition in children who are born without a thyroid gland or who have a nonfunctioning gland. This can lead to poor growth and development as well as mental retardation.
  • Hyperthyroidism occurs when excessive amounts of thyroid hormones are produced and released into circulation. Graves’ disease is the most common cause of hyperthyroidism.

Thyroid Hormones


Description

  • Thyroid hormones are made available to replace the low or absent levels of natural thyroid hormone and suppress the overproduction of TSH by the pituitary.
  • These can contain both natural and synthetic thyroid hormone.

Therapeutic Action

The desired and beneficial action of thyroid hormones:

  • This is replacement hormone for hypothyroid states like myxedema coma, goiters, and thyroid cancer increases the metabolic rate of body tissues, increasing oxygen consumption, respiration, heart rate, growth and maturation, and the metabolism of fats, carbohydrates, and proteins.  
  • Levothyroxine, a synthetic salt of T4, is the most frequently used replacement hormone because of its predictable bioavailability and reliability.

Indications

Thyroid hormones are indicated for the following medical conditions:

  • Replacement hormone for hypothyroid states like myxedema coma, goiters, and thyroid cancer
  • Treatment for thyroid toxicity in conjunction with antithyroid drugs
  • Treatment for thyroid overstimulation during pregnancy

Pharmacokinetics

Here are the characteristic interactions of thyroid hormones and the body in terms of absorption, distribution, metabolism, and excretion:

Route Onset Peak Duration
PO Slow 1-3 wk 1-3 wk
IV 6-8 h 24-48 h Unknown
T1/2: 6-7 d
Metabolism: liver
Excretion: bile

Contraindications and Cautions

The following are contraindications and cautions for the use of thyroid hormones:

  • Allergy to any component of the drug. To prevent hypersensitivity reactions.
  • Acute thyrotoxicosis (unless used in conjunction with antithyroid drugs). Can be exacerbated by the drugs
  • Myocardial infarction. Can be exacerbated by the drugs
  • Lactation. Drug enters breast milk and can suppress infant’s thyroid production
  • Addison disease. Body will not be able to deal with drug effects.
  • Pregnancy. Potential adverse effects on the fetus
  • Liothyronine and liorix have greater incidence of cardiac side effects.

Adverse Effects

Use of thyroid and hormones may result to these adverse effects:

  • Skin reactions and loss of hair
  • Symptoms of hyperthyroidism

Interactions

The following are drug-drug interactions involved in the use of thyroid hormones:

  • Cholestyramine. Decreased absorption of thyroid hormones (take two hours apart)
  • Anticoagulants. Increased bleeding
  • Digitalis glycosides. Decreased effectiveness of digitalis glycosides.   

Nursing Considerations

Here are important nursing considerations when administering thyroid hormones:

Nursing Assessment

These are the important things the nurse should include in conducting assessment, history taking, and examination:

  • Assess for contraindications or cautions (e.g. history of allergy, pregnancy, Addison disease, etc.) to avoid adverse effects.
  • Assess skin lesions; orientation and affect; blood pressure, pulse, peripheral perfusion, and vessel evaluation; respiration and adventitious breath sounds; thyroid function test to determine baseline status before beginning therapy and for any potential adverse effects.
Nursing Diagnoses

Here are some of the nursing diagnoses that can be formulated in the use of this drug for therapy:

Implementation with Rationale

These are vital nursing interventions done in patients who are taking thyroid hormones:

  • Administer a single daily dose before breakfast each day to ensure consistent therapeutic levels.
  • Administer with a full glass of water to prevent difficulty of swallowing and esophageal atresia.
  • Monitor cardiac response to detect cardiac adverse effects.
  • Arrange for periodic blood tests of thyroid function to monitor the effectiveness of the therapy.
  • Provide comfort measures (temperature control, rest as needed, safety precautions) to help patient cope with drug effects.
  • Provide patient education about drug effects and warning signs to report to enhance patient knowledge and to promote compliance.
Evaluation

Here are aspects of care that should be evaluated to determine effectiveness of drug therapy:

  • Monitor patient response to therapy (return of metabolism to normal, prevention of goiter).
  • Monitor for adverse effects (tachycardia, hypertension, anxiety, skin rash).
  • Evaluate patient understanding on drug therapy by asking patient to name the drug, its indication, and adverse effects to watch for.
  • Monitor patient compliance to drug therapy.

Antithyroid Agents


Description

  • Antithyroid agents are drugs used to block the production of thyroid hormone and treat hyperthyroidism.
  • This include thioamides and iodide solutions. These groups of drugs are not chemically related but they both block the formation of thyroid hormones within the thyroid gland.

Therapeutic Action

The desired and beneficial action of antithyroid agents:

  • Thioamides lower thyroid hormones by preventing the formation of thyroid hormone in the thyroid cells. They also partially inhibit the conversion of T4 to T3 at cellular level. Thioamides include propylthiouracil (PTU) and methimazole.
  • Iodine solutions in high doses block thyroid function. They cause the cells to become oversaturated with iodine and stop producing hormones.

Indications

Antithyroid agents are indicated for the following medical conditions:

  • Treatment of hyperthyroidism
  • Thyroid blocking in a radiation emergency

Pharmacokinetics

Here are the characteristic interactions of thioamides and the body in terms of absorption, distribution, metabolism, and excretion:

Route Onset Peak Duration
PO 30-60 min 2-4 h
T1/2: 6-13 h
Metabolism: –
Excretion: urine

 

Here are the characteristic interactions of iodine solutions and the body in terms of absorption, distribution, metabolism, and excretion:

Route Onset Peak Duration
PO 24 h 10-15 d 6 wk
T1/2: unknown
Metabolism: liver
Excretion: urine

Contraindications and Cautions

The following are contraindications and cautions for the use of antithyroid agents:

  • Allergy to any component of the drug. To prevent hypersensitivity reactions.
  • Pregnancy. Development of cretinism. PTU is the drug of choice for pregnant women.
  • Lactation. Risk of antithyroid activity in the infant (neonatal goiter)
  • Pulmonary edema or tuberculosis. Contraindicated with strong iodine products.

Adverse Effects

Use of antithyroid agents may result to these adverse effects:

  • Thioamides: drowsiness, lethargy, bradycardia, nausea, skin rash
  • PTU: nausea, vomiting, GI complaints, severe liver toxicity
  • Methimazole: bone marrow suppression
  • Iodine solution: hypothyroidism; metallic taste and burning sensation in the mouth, sore teeth and gums, diarrhea; staining of teeth, skin rash, and development of goiter. I131 is only for patients over 30 years old because of adverse effects associated with radioactivity.

Interactions

The following are drug-drug interactions involved in the use of antithyroid agents:

  • Thioamides: increased bleeding with oral anticoagulants and PTU
  • Iodine solutions: changes in the metabolism and level of anticoagulants, theophylline, digoxin, metoprolol, and propranolol

Nursing Considerations

Here are important nursing considerations when administering antithyroid agents:

Nursing Assessment

These are the important things the nurse should include in conducting assessment, history taking, and examination:

  • Assess for contraindications or cautions (e.g. history of allergy, renal stone, pregnancy, etc.) to avoid adverse effects.
  • Assess skin lesions; orientation and affect; liver evaluation; serum calcium, magnesium, and alkaline phosphate levels; and radiographs of bones as appropriate, to determine baseline status before beginning therapy and for any potential adverse effects.
Nursing Diagnoses

Here are some of the nursing diagnoses that can be formulated in the use of this drug for therapy:

Implementation with Rationale

These are vital nursing interventions done in patients who are taking antithyroid agents:

  • Administer PTU three times a day, around the clock to ensure consistent therapeutic levels.
  • Give iodine solution through a straw to decrease staining of teeth; tables can be crushed.
  • Provide comfort measures to help patient cope with drug effects.
  • Provide patient education about drug effects and warning signs to report to enhance patient knowledge and to promote compliance.
Evaluation

Here are aspects of care that should be evaluated to determine effectiveness of drug therapy:

  • Monitor patient response to therapy (lowering of thyroid hormone levels).
  • Monitor for adverse effects (bradycardia, anxiety, blood dyscrasias).
  • Evaluate patient understanding on drug therapy by asking patient to name the drug, its indication, and adverse effects to watch for.
  • Monitor patient compliance to drug therapy.

Practice Quiz: Thyroid Agents


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1. This is the most common type of thyroid dysfunction.

A. Cretinism
B. Myxedema coma
C. Hyperthyroidism
D. Hypothyroidism

1. Answer: D. Hypothyroidism

Hypothyroidism is a lack of sufficient levels of thyroid hormones to maintain a normal metabolism. This is the most common type of thyroid dysfunction and is common among older women and men. Symptoms include obesity and fatigue, among others.

2. Thyroid hormones can:

A. stimulate overproduction of TSH
B. increase oxygen consumption
C. increase the heart rate without affecting the respirations
D. retard growth and maturation

2. Answer: B. increase oxygen consumption

Thyroid hormones increase the metabolic rate of body tissues, increasing oxygen consumption, respiration, heart rate, growth and maturation, and the metabolism of fats, carbohydrates, and proteins.

3. All of the following should be included in the nursing interventions for patients taking thyroid hormones, except:

A. consistent administration before breakfast each day
B. monitor cardiac response
C. advise patient to frequently exercise to develop the core
D. provide for temperature control and safety precautions

3. Answer: C. advise patient to frequently exercise to develop the core

As much as possible, patients should be provided for rest periods when on this therapy.

4. The antithyroid agent of choice for pregnant women.

A. methimazole
B. PTU
C. levothyroxine
D. iodine solution

4. Answer: B. PTU

Other antithyroid agents can lead to development of cretinism.

5. Which of the following history data will possibly render strong iodine products contraindicated for the patient?

A. 35 years old
B. history of blood-tinged sputum for the past three weeks
C. intake of oral anticoagulants
D. both B and C

5. Answer: D. both B and C

A blood-tinged sputum for the past three weeks may signify tuberculosis. If this is the case, strong iodine products are contraindicated. Also, strong iodine products can change the metabolism and level of anticoagulants and may place the patient at greater risk for bleeding. Lastly, I131 is only for patients over 30 years old because of adverse effects associated with radioactivity.

See Also


Here are other nursing pharmacology study guides:

Endocrine System Drugs

Autonomic Nervous System Drugs

Immune System Drugs

Chemotherapeutic Agents

Reproductive System Drugs

Nervous System Drugs

Cardiovascular System Drugs

Further Reading and Resources


Recommended resources and books:

  1. Focus on Nursing Pharmacology - Easy to follow guide for Pharmacology
  2. NCLEX-RN Drug Guide: 300 Medications You Need to Know for the Exam - Great if you're reviewing for the NCLEX
  3. Nursing 2017 Drug Handbook (Nursing Drug Handbook) - Reliable nursing drug handbook!
  4. Lehne's Pharmacology for Nursing Care - Provides key information on commonly used drugs in nursing
  5. Pharmacology and the Nursing Process - Learn how to administer drugs correctly and safely!
  6. Pharm Phlash Cards!: Pharmacology Flash Cards - Flash Cards for Nursing Pharmacology