Thyroid Agents

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 Contents

• Thyroid Agents: Generic and Brand Names
• Disease Spotlight: Thyroid Dysfunction
• Thyroid Hormones
  • Therapeutic Action
  • Indications
  • Pharmacokinetics
  • Contraindications and Cautions
  • Adverse Effects
  • Interactions
  • Nursing Considerations
    • Nursing Assessment
    • Nursing Diagnoses
    • Implementation with Rationale
    • Evaluation
• Antithyroid Agents
  • Therapeutic Action
  • Indications
  • Pharmacokinetics
  • Contraindications and Cautions
  • Adverse Effects
  • Interactions
  • Nursing Considerations
    • Nursing Assessment
    • Nursing Diagnoses
    • Implementation with Rationale
    • Evaluation
• Recommended Resources
• See Also
• References and Sources

Thyroid Agents: Generic and Brand Names

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

• Thyroid agents
  • Thyroid hormones
    • levothyroxine (Synthroid, Levoxyl)
    • liothyronine (Cytomel, Triostat)
    • liotrix (Thyrolar)
    • thyroid desiccated extract (Armour 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

• 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

Half-life (T1/2)	Metabolism	Excretion
6-7 d	Liver	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:

• Decreased cardiac output related to CV effects
• Imbalanced nutrition: less than body requirements related to changes in metabolism
• Ineffective tissue perfusion related to thyroid activity

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

• 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: PO
  • Onset: 30-60 min
  • Peak: Not specified
  • Duration: 2-4 h
• Half-life (T1/2): 6-13 h
• Metabolism: Not specified

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

• Route: PO
  • Onset: 24 h
  • Peak: 10-15 days
  • Duration: 6 weeks
• Half-life (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:

• Imbalanced nutrition: more than body requirements related to metabolic changes
• Risk for injury related to bone marrow suppression

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.

Recommended Resources

Our recommended nursing pharmacology resources and books:

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See Also

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• Nursing Pharmacology – Study Guide for Nurses
  Our collection of topics related to nursing pharmacology
• Pharmacology Nursing Mnemonics & Tips
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• Generic Drug Name Stems Cheat Sheet
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• Common Drugs and Their Antidotes
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• IV Fluids and Solutions Guide & Cheat Sheet
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• Drug Dosage Calculations NCLEX Practice Questions (100+ Items)
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References and Sources

References and sources for this pharmacology guide for Thyroid agents:

• Karch, A. M., & Karch. (2011). Focus on nursing pharmacology. Wolters Kluwer Health/Lippincott Williams & Wilkins. [Link]
• Katzung, B. G. (2017). Basic and clinical pharmacology. McGraw-Hill Education.
• Lehne, R. A., Moore, L. A., Crosby, L. J., & Hamilton, D. B. (2004). Pharmacology for nursing care.
• Smeltzer, S. C., & Bare, B. G. (1992). Brunner & Suddarth’s textbook of medical-surgical nursing. Philadelphia: JB Lippincott.