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CHAPTER 31
Thyroid and Antithyroid Drugs
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Thyroid Gland
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Secretes three hormones essential for proper
regulation of metabolism
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Thyroxine (T4)
Triiodothyronine (T3)
Calcitonin
Located near the parathyroid gland, which is
responsible for maintaining adequate levels
of calcium in the extracellular fluid
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Hypothyroidism:
Deficiency in Thyroid Hormones
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Primary: abnormality in the thyroid gland itself
Secondary: results when the pituitary gland is
dysfunctional and does not secrete TSH
Tertiary: results when the hypothalamus
gland does not secrete TRH, which stimulates
the release of TSH
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Hypothyroidism
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Cretinism
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Hyposecretion of thyroid hormone during youth
Low metabolic rate, retarded growth and sexual
development, possible mental retardation
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Hypothyroidism (cont’d)
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Myxedema
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Hyposecretion of thyroid hormone during
adulthood
Decreased metabolic rate, loss of mental and
physical stamina, weight gain, loss of hair, firm
edema, yellow dullness of the skin
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Hypothyroidism (cont’d)
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Goiter
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Enlargement of the thyroid gland
Results from overstimulation by elevated levels of
TSH
TSH is elevated because there is little or no
thyroid hormone in circulation
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Hypothyroidism (cont’d)
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Common symptoms
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Thickened skin
Hair loss
Constipation
Lethargy
Anorexia
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Thyroid Preparations
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levothyroxine (Synthroid, Levothyroid)
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liothyronine (Cytomel)
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Synthetic thyroid hormone T3
liotrix (Thyrolar)
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Synthetic thyroid hormone T4
Synthetic thyroid hormone T3 and T4 combined
thyroid
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Desiccated (dried) animal thyroid gland
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Mechanism of Action
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Thyroid preparations are given to replace
what the thyroid gland cannot produce to
achieve normal thyroid levels (euthyroid)
Thyroid drugs work the same way as thyroid
hormones
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Indications
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To treat all three forms of hypothyroidism
Levothyroxine is the preferred drug because its
hormonal content is standardized; therefore, its
effect is predictable
“Euthyroid”
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Indications (cont’d)
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Also used for thyroid replacement in patients
whose thyroid glands have been surgically
removed or destroyed by radioactive iodine in
the treatment of thyroid cancer or
hyperthyroidism
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Adverse Effects
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Cardiac dysrhythmia is the most significant
adverse effect
May also cause:
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Tachycardia, palpitations, angina, hypertension,
insomnia, tremors, headache, anxiety, nausea,
diarrhea, menstrual irregularities, weight loss,
appetite changes, sweating, heat intolerance,
others
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Hyperthyroidism:
Excessive Thyroid Hormones
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Caused by several diseases
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Graves’ disease
Multinodular disease
Plummer’s disease (rare)
• Also called toxic nodular disease
Thyroid storm (induced by stress or infection)
• Severe and potentially life-threatening
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Hyperthyroidism
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Affects multiple body systems, resulting in an
overall increase in metabolism
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Diarrhea
 Flushing
 Increased appetite
 Muscle weakness
 Sleep disorders
 Altered menstrual flow
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Fatigue
Palpitations
Nervousness
 Heat intolerance
 Irritability
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Treatment of Hyperthyroidism
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Radioactive iodine (I131) works by destroying
the thyroid gland
Surgery to remove all or part of the thyroid
gland
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Lifelong thyroid hormone replacement will be
needed
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Treatment of Hyperthyroidism
(cont’d)
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Antithyroid drugs: thioamide derivatives
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methimazole (Tapazole)
propylthiouracil (PTU)
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Antithyroid Drugs
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Used to palliate hyperthyroidism and to
prevent the surge in thyroid hormones that
occurs after surgical treatment or during
radioactive iodine treatment for
hyperthyroidism
May cause liver and bone marrow toxicity
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Nursing Implications
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Assess for drug allergies, contraindications,
potential drug interactions
Obtain baseline vital signs, weight
Cautious use advised for those with cardiac
disease, hypertension, and pregnant women
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Nursing Implications (cont’d)
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During pregnancy, treatment for
hypothyroidism should continue
Fetal growth may be retarded if maternal
hypothyroidism is untreated during pregnancy
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Adjust dosage every 4 weeks to keep TSH at the
lower end of the normal range
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Nursing Implications (cont’d)
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Teach patient to take thyroid drugs once daily
in the morning to decrease the likelihood of
insomnia if taken later in the day
Teach patient to take the medications at the
same time every day and not to switch brands
without physician approval
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Nursing Implications (cont’d)
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Teach patients to report any unusual
symptoms, chest pain, or heart palpitations
Teach patients not to take over-the-counter
medications without physician approval
Teach patients that therapeutic effects may
take several months to occur
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Nursing Implications (cont’d)
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Teach patients the importance of alerting
health care providers of thyroid medication
use
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May enhance activity of anticoagulants
 Diabetic patients may need increased dosages of
hypoglycemic meds
 May decrease serum digoxin levels
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Nursing Implications (cont’d)
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Antithyroid medications
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Better tolerated when given with food
Give at the same time each day to maintain
consistent blood levels
Never stop these medications abruptly
Avoid eating foods high in iodine (seafood, soy
sauce, tofu, and iodized salt)
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Nursing Implications (cont’d)
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Monitor for therapeutic response
Monitor for adverse effects
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