27.2: Thyroid and Antithyroid Drugs
By the end of this section, you should be able to:
- 27.2.1 Identify the characteristics of thyroid and antithyroid drugs used to treat thyroid disorders.
- 27.2.2 Explain the indications, actions, adverse reactions, contraindications, and interactions of thyroid and antithyroid drugs used to treat thyroid disorders.
- 27.2.3 Describe nursing implications of thyroid and antithyroid drugs used to treat thyroid disorders.
- 27.2.4 Explain the client education related to thyroid and antithyroid drugs used to treat thyroid disorders.
Thyroid Drugs
Thyroid drugs are used when the thyroid is functioning incorrectly and there is a need to replace the thyroid hormone so that the body can maintain its expected function. Thyroid drugs can be synthetic thyroid hormones or animal-based thyroid hormones. These drugs act by replacing the body’s natural thyroid hormone when the levels are low or absent within the body.
Levothyroxine Sodium
Levothyroxine sodium is a synthetic thyroid hormone that is identical to T4 produced in the body. The gastrointestinal tract absorbs 40%–80% of this synthetic hormone. The drug is greater than 99% protein bound and easily distributed. It is primarily eliminated by the kidneys, with approximately 20% of T4 being excreted in the stool (Eghtedari & Correa, 2022). It comes in tablet and injectable forms and is used to treat hypothyroidism and pituitary TSH suppression. Levothyroxine is contraindicated in clients with uncorrected adrenal insufficiency: because of the role of adrenal glands in regulating stress response and cortisol production, levothyroxine’s ability to increase metabolic demands and stress may overwhelm the impaired adrenal glands, causing an adrenal crisis. Stabilization of adrenal function is crucial before starting levothyroxine treatment to prevent an adrenal crisis.
Levothyroxine sodium has a narrow therapeutic index; careful dose titration is necessary to avoid overtreatment or undertreatment. Clients should take this drug in the morning at least 30 minutes before consuming food or fluid containing caffeine such as coffee, tea, or soda. Food and caffeinated drinks can both interfere with the absorption of levothyroxine sodium.
Liothyronine Sodium
Liothyronine sodium is a synthetic thyroid hormone mimicking T3. This hormone replacement is commonly used to treat hypothyroidism and myxedema coma. Liothyronine can be taken orally, comes in an intravenous form, and is easily absorbed and readily distributed in the body. As with levothyroxine, liothyronine is contraindicated in clients with uncorrected adrenal insufficiency. As stated above, the adrenal glands control the stress response and cortisol levels within the body. When they are impaired, they are unable to handle the increase in metabolic rate caused by the administration of liothyronine, leading to an adrenal crisis. Adverse effects of liothyronine include anxiety, blurred vision, chest discomfort, decreased bone mineral density, and decreased urine output.
Safety Alert
Similarly Named Drugs
Do not confuse levothyroxine sodium with liothyronine sodium. Although these drugs are in the same drug class, they require different dosing and lab monitoring.
Desiccated Thyroid Extract
Desiccated thyroid extract is a thyroid hormone developed from pig glands that is often used as an over-the-counter remedy for thyroid hormone replacement. Desiccated thyroid extract has not been approved by the Food and Drug Administration (FDA) due to a complex manufacturing process leading to issues with safety, effectiveness, and quality, with inconsistent or inaccurate dosage. Table 27.2 lists common thyroid drugs and typical routes and dosing for adult clients.
| Drug | Routes and Dosage Ranges |
|---|---|
| Levothyroxine sodium ( Synthroid , Levoxyl ) |
Individualized dosing due to a narrow therapeutic index.
Standard dosing starts at 1.6 mcg/kg/day orally; increase by 12.5–25 mcg orally every 4–6 weeks if needed. Serum T4 levels should be used to monitor therapeutic dosing range of drug. Must be titrated based on the individual’s need and to avoid the consequences of overtreatment or undertreatment. |
|
Liothyronine sodium
( Cytomel , Triostat ) |
25 mcg orally once daily; increase by 25 mcg orally daily every 1–2 weeks if needed.
Maintenance dose: 25–75 mcg once daily. Serum T3 levels should be used to monitor therapeutic dosing range of drug. |
Adverse Effects and Contraindications
Common adverse effects among the thyroid drug classification include cardiac effects—such as tachycardia, palpitations, and arrhythmias—weight loss, nervousness and irritability, heat intolerance, diarrhea, abdominal cramping, headaches, and sleep disturbances.
Contraindications for thyroid drug classification include hypersensitivity to the drug or any of its components as well as any recent myocardial infarction because thyroid drugs can increase heart rate and heart contractility. Untreated adrenal insufficiency is a contraindication because impaired adrenal glands cannot handle the increased metabolic rate cause by thyroid drugs, as is hyperthyroidism since the drugs would increase thyroid hormone levels that are already elevated.
Table 27.3 is a drug prototype table for thyroid drugs featuring levothyroxine sodium. It lists drug class, mechanism of action, adult dosage, indications, therapeutic effects, drug and food interactions, adverse effects, and contraindications.
|
Drug Class
Thyroid hormone Mechanism of Action Replaces the amount of hormone the thyroid is unable to produce, helping to restore thyroid hormone homeostasis within the body |
Drug Dosage
Individualized dosing due to a narrow therapeutic index. Standard dosing starts at 1.6 mcg/kg/day orally; increase by 12.5–25 mcg orally every 4–6 weeks if needed. Serum T4 levels should be used to monitor therapeutic dosing range of drug. Must be titrated based on the individual’s need and to avoid the consequences of overtreatment or undertreatment. |
|
Indications
Hypothyroidism Pituitary TSH suppression Therapeutic Effects Restores thyroid hormone levels to normal Maintains thyroid hormone homeostasis |
Drug Interactions
Dopamine Glucocorticoids Octreotide Amiodarone Digitalis Iodine Lithium Calcium Iron Warfarin Food Interactions Soy Soybean flour Cotton seed meal Walnuts Dietary fiber may bind to levothyroxine sodium and decrease its absorption |
|
Adverse Effects
Irregular heartbeat Heat intolerance Irregular breathing Irritability Nausea Tremors Decreased urine output |
Contraindications
Adrenal insufficiency Nontoxic goiter or nodular thyroid disease Caution: Monitor closely when administering to older clients who have underlying cardiovascular disease—may precipitate thyrotoxicosis |
Nursing Implications
The nurse should do the following for clients who are taking thyroid drugs:
- Educate the client that thyroid replacement hormone is a lifelong therapy.
- Assess the client’s knowledge about signs and symptoms of over- and undertreatment, adverse reactions, and contraindications and clarify any gaps in knowledge.
- Monitor thyroid functioning of the client and report any abnormalities or symptoms of thyroid storm, such as tachycardia, cardiac dysrhythmias, fever, heart failure, flushed skin, confusion, behavioral changes, and hypotension, to the health care provider.
- Provide client teaching regarding the drug and when to call the health care provider. See below for client teaching guidelines.
Client Teaching Guidelines
The client taking a thyroid drug should:
- Take on an empty stomach 1/2–1 hour before breakfast for better absorption.
- Keep a journal of their symptoms. It may take several weeks for them to notice improved symptoms.
- Report symptoms of irregular heartbeat, chest pain, shortness of breath, leg cramps, headache, nervousness, irritability, sleeplessness, and heat intolerance to their health care provider because these may represent an adverse reaction or toxicity to the drug.
- Notify the health care provider if they are pregnant or become pregnant because the dose of the drug may need to be increased during pregnancy.
- Store out of reach of children and away from heat, moisture, and light.
The client taking a thyroid drug should not :
- Stop taking unless directed by their health care provider because this drug class replaces their body’s missing thyroid hormone.
- Take with food because it will decrease the drug’s absorption.
- Take within 4 hours of taking calcium and/or iron supplements, including calcium antacids, because they may impact the drug’s absorption.
FDA Black Box Warning
Thyroid Hormones
Thyroid hormones, including levothyroxine sodium, either alone or with other therapeutic agents, should not be used for treatment of obesity or weight loss due to producing serious toxicity or life-threatening manifestations.
Antithyroid Drugs
Antithyroid drugs are used to inhibit production of the thyroid hormone so that the body can maintain normal thyroid homeostasis. Antithyroid drugs act by inhibiting the synthesis of thyroid hormones or by inundating the thyroid gland with iodine to prevent thyroid hormone release. Antithyroid drugs are used when the thyroid hormone levels are elevated within the body.
Thionamides
Thionamides are compounds that effectively hinder the synthesis of thyroid hormones. These compounds are transported into the thyroid gland and act by inhibiting two critical processes: organification of iodine to tyrosine residues in thyroglobulin as well as coupling of iodotyrosines , leading to lower serum levels of thyroid hormones. The process of organification of iodine to tyrosine residues refers to the incorporation of iodine atoms into tyrosine amino acid molecules within the structure of thyroglobulin, a protein produced by the thyroid gland. This is an essential step in the synthesis of thyroid hormones. The coupling of iodotyrosines refers to the binding together of iodinated tyrosine molecules within the thyroglobulin to form the final thyroid hormones T3 and T4. Thionamides are used in the treatment of hyperthyroidism and Graves’ disease. Thionamides include methimazole and propylthiouracil.
Methimazole
Methimazole inhibits the synthesis of thyroid hormones and is indicated to treat hyperthyroidism. This medication is rapidly absorbed in the gastrointestinal tract and metabolized rapidly. It is excreted mainly in the urine but is excreted in breast milk and should be used cautiously with clients who are breastfeeding. Careful dose titration is necessary to avoid overtreatment or undertreatment. When the client develops toxicity to methimazole, symptoms such as nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, edema, and agranulocytosis may develop (Armstrong et al., 2022; DailyMed, Methimazole, 2022; Shahid et al., 2022; Singh & Correa, 2022).
Propylthiouracil
Propylthiouracil inhibits the synthesis of thyroid hormones. This drug is readily absorbed and extensively metabolized; it is mainly excreted in the urine. Propylthiouracil is indicated for Graves’ disease with hyperthyroidism, multinodular goiter , and to ameliorate symptoms of hyperthyroidism before thyroidectomy or radioactive iodine therapy in clients who did not tolerate methimazole. It is contraindicated in clients with hypersensitivity and with liver failure. Adverse effects include hepatitis, jaundice, anemia, thrombocytopenia, nephritis, arthralgia, and paresthesia.
Iodine
The body naturally uses iodine for the formation of thyroid hormone. Iodine solutions cause the thyroid cells to become inundated with iodine, thereby decreasing thyroid hormone production. Iodine preparations are used to treat hyperthyroidism when thionamides are ineffective or for those clients who are not candidates for surgery.
Potassium Iodide
Potassium iodide prevents iodine from getting into the thyroid gland. As a medication, potassium iodine is used two separate ways: 1) to treat hyperthyroidism by inhibiting thyroid hormone secretion in very acute situations, and 2) to prevent the uptake of radioactive iodine in the event of a nuclear emergency. Additional use includes radioactive iodine to ablate a hyperactive thyroid gland. Adverse effects include skin rash, shortness of breath, wheezing, swelling, fever, and joint pain. It is contraindicated in those who have had an allergic reaction to iodine and those with nodular thyroid disease. ThyroShield and Thyrosafe are the only FDA-approved brands of potassium iodide.
Table 27.4 lists common antithyroid drugs and typical routes and dosing for adult clients.
| Drug | Routes and Dosage Ranges |
|---|---|
|
Methimazole
( Tapazole ) |
Mild hyperthyroidism:
15 mg orally daily.
Moderate hyperthyroidism: 30–40 mg orally daily. Severe hyperthyroidism: 60 mg orally daily, divided into 3 doses at 8-hour intervals. Maintenance dose: 5–15 mg orally daily. |
|
Propylthiouracil
( PTU ) |
300–400 mg orally daily; maintenance dose 100–150 mg orally daily. |
| Potassium iodide ( Thyrosafe ) | 130 mg orally daily at 24-hour intervals. |
Adverse Effects and Contraindications
Common adverse effects include:
- Rash or skin reactions—pruritis and hives
- Gastrointestinal symptoms—nausea and vomiting
- Liver toxicity—jaundice, dark urine, abdominal pain, fatigue
- Bone marrow suppression—decreased white blood cell, red blood cell, and platelet production leading to unexplained fever, sore throat, easy bruising, bleeding, and fatigue
- Hypothyroidism—increased fatigue, weight gain, cold intolerance, constipation
Contraindications include hypersensitivity to the drug or any of its components, severe liver disease or impairment, and with pregnancy or breastfeeding because the drugs can cross the placenta, be excreted in breast milk, and potentially affect the development of the fetus or infant.
Table 27.5 is a drug prototype table for antithyroid drugs featuring methimazole. It lists drug class, mechanism of action, adult dosage, indications, therapeutic effects, drug and food interactions, adverse effects, and contraindications.
|
Drug Class
Antithyroid agent Mechanism of Action Inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism |
Drug Dosage
Mild hyperthyroidism: 15 mg orally daily. Moderate hyperthyroidism: 30–40 mg orally daily. Severe hyperthyroidism: 60 mg orally daily, divided into 3 doses at 8-hour intervals. Maintenance dose: 5–15 mg orally daily. |
|
Indications
Hyperthyroidism Ameliorating hyperthyroidism in preparation for subtotal thyroidectomy or radioactive iodine therapy When thyroidectomy is contraindicated or not advisable Therapeutic Effects Lowers thyroid hormone levels Relieves/reduces manifestations of hyperthyroidism |
Drug Interactions
Anticoagulants Beta-adrenergic blockers Digitalis glycosides Theophylline Food Interactions No significant interactions |
|
Adverse Effects
Agranulocytosis Thrombocytopenia Aplastic anemia Fever Insulin autoimmune syndrome (low blood glucose levels) Jaundice Urticaria Epigastric distress Arthralgia |
Contraindications
Hypersensitivity Pregnancy and breastfeeding Caution: Monitor closely for agranulocytosis and hepatotoxicity |
Nursing Implications
The nurse should do the following for clients who are taking antithyroid drugs:
- Monitor complete blood cell count and coagulation studies, liver studies, and thyroid levels and report abnormalities to the health care provider.
- Check with the health care provider before administering antithyroid drugs if the client is currently taking anticoagulants, beta-adrenergic blockers and digitalis glycosides, or theophylline, which stimulates the central nervous system and when taken with antithyroid drugs can impact mood, behavior, cognition, and sleep patterns.
- Provide client teaching regarding the drug and when to call the health care provider. See below for additional client teaching guidelines.
Client Teaching Guidelines
The client taking an antithyroid drug should:
- Take the drug exactly as prescribed by the health care provider.
- Report sore throat, skin eruptions, fever, headache, or general malaise to the health care provider because these may be symptoms of a severe reaction.
- Monitor weight weekly and report a weight gain of 3 pounds in 24 hours or 5 pounds in a week to the health care provider.
- Notify the health care provider if they are pregnant or plan to become pregnant or if they are breastfeeding.
- Store out of reach of children and away from heat, moisture, and light.
The client taking an antithyroid drug should not:
- Eat dietary sources of iodine (iodized salt, shellfish) without speaking with the health care provider first.
FDA Black Box Warning
Propylthiouracil
Severe liver injury and acute liver failure have been reported in clients treated with propylthiouracil.
Case Study
Read the following clinical scenario to answer the questions that follow.
Ellis Dominico is a 40-year-old client who visits their primary health care provider’s office for a checkup. Ellis reports fatigue and decreased energy, constipation, and having an intolerance to cold temperatures.
History
Hyperthyroidism (diagnosed 6 months ago)
Current Medications
Methimazole, 15 mg orally daily
| Vital Signs | Physical Examination | |
|---|---|---|
| Temperature: | 98.3°F |
|
| Blood pressure : | 96/58 mm Hg | |
| Heart rate: | 58 beats/min | |
| Respiratory rate : | 18 breaths/min | |
| Oxygen saturation : | 95% on room air | |
| Height : | 5'6" | |
| Weight : | 211 lb (10 lb heavier than weight 3 months ago) |
Based on the assessment findings, which health condition does the nurse anticipate the health care provider will identify?
- Answer
-
Hypothyroidism
Which diagnostic test should the nurse anticipate the health care provider will order for Ellis?
- Answer
-
TSH