Thyroid Disorders and Drugs

• Thyroid disorders involve the use of thyroid and anti-thyroid drugs

Thyroid Gland

• Secretes three hormones essential for regulation of metabolism.
• The three hormones are thyroxine (T4), triiodothyronine (T3), and calcitonin.
• Calcitonin helps build T3 and T4.
• Iodine is needed to convert T4 to T3.
• The thyroid gland is located near the parathyroid gland.
• The parathyroid gland is responsible for maintaining adequate levels of calcium in the extracellular fluid.

Hypothyroidism

• Hypothyroidism can be primary, secondary, or tertiary.
• Primary hypothyroidism is a gland issue and most common.
• Primary hypothyroidism is related to destruction of thyroid tissue or defective hormone synthesis.
• Hormone findings for primary hypothyroidism include decreased T3 and T4 levels and increased thyroid stimulating hormone (TSH) levels.
• Secondary hypothyroidism is rare.
• Secondary hypothyroidism is related to pituitary disease with decreased TSH secretion.
• Tertiary hypothyroidism involves a reduce level of thyrotropin releasing hormone (TRH) from the hypothalamus.
• Hypothyroidism may be transient, related to thyroiditis, or a result from discontinuing thyroid hormone therapy.
• Congenital hypothyroidism involves hyposecretion of thyroid hormone during youth
• Congenital hypothyroidism presents with a low metabolic rate, retarded growth and sexual development, and slowed mental development.
• Myxedema involves hyposecretion of thyroid hormone during adulthood.
• Myxedema presents with a decreased metabolic rate, loss of mental and physical stamina, weight gain, loss of hair, firm edema, yellow dullness of the skin.
• Goiter is the enlargement of the thyroid gland.
• Goiter results from overstimulation by elevated levels of TSH.
• TSH is elevated because there is little or no thyroid hormone in circulation.

Goiter Process

• Hypothalamus releases TRH
• Pituitary releases TSH
• Thyroid gland does not produce T4 & T3
• There is no message to stop TRH & TSH
• Results from overstimulation by elevated levels of TSH
• TSH is elevated because there is little or no thyroid hormone in circulation.
• Iodine deficiency requires iodine to convert T4 to T3 and is the most common cause worldwide, especially in iodine-deficient areas.
• In locations where iodine intake is adequate, the primary cause is atrophy of the gland.
• May also develop because of treatment for hyperthyroidism (Graves Disease)
• Treatment essentially kills the gland to stop the over production of thyroid hormones leaving the gland unproductive, pts will need lifelong thyroid replacements
• Amiodarone and lithium can cause hypothyroidism.
• Hypothyroidism clinical manifestations vary depending on severity, duration, and age of onset.
• There are systemic effects characterized by slowing of body processes.
• There is a range from no symptoms to classic symptoms and physical changes easily detected on examination.
• Onset of symptoms may occur over months to years, unless occurring after thyroidectomy, thyroid ablation or treatment with antithyroid drugs

Myxedema Coma

• Myxedema Coma presents with mental sluggishness and drowsiness.
• Myxedema Coma presents with lethargy progressing gradually or suddenly to impairment of consciousness or coma.
• Myxedema Coma is precipitated by infection, drugs (especially opioids, tranquilizers, & barbiturates), exposure to cold, or trauma.
• Myxedema Coma is characterized by subnormal temperature, hypotension, and hypoventilation.
• For the patient to survive, vital functions must be supported and IV thyroid hormone replacement must be administered.

Thyroid Replacement Drug Therapy

• The names of some levothyroxine drugs are Synthroid, Levothyroid, Levoxyl.
• Levothyroxine is a synthetic thyroid hormone T4.
• Liothyronine (Cytomel) is a synthetic thyroid hormone T3.
• Liotrix (Thyrolar) is a synthetic thyroid hormone T3 and T4 combined.
• Oral medication are administered 1/2 hour to 1 hour before breakfast to facilitate absorption.
• Thyroid hormones are a synthetic form of thyroxine (T4), a form of liothyronine (T3), or a combination of T3 and T4.
• These increase metabolic rate, protein synthesis, cardiac output, renal perfusion, oxygen use, body temperature, blood volume and growth process.
• Thyroid preparations are given to replace what the thyroid gland cannot produce to achieve normal thyroid levels (euthyroid).
• Treats all three forms of hypothyroidism.
• Levothyroxine is the preferred drug because its hormonal content is standardized and its effect is predictable.
• It is 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.
• Is used for emergency treatment of myxedema coma.
• Is used for Hypothyroidism in pregnancy
• Adverse effects of thyroid drug therapy includes cardiac dysrhythmia which is the most significant adverse effect.
• Other adverse effects are tachycardia, palpitations, angina, hypertension, insomnia, tremors, headache, heat intolerance, sweating, appetite changes, weight loss, menstrual irregularities, diarrhea, nausea, and anxiety.
• All medications can result in hyperthyroidism.
• Contraindications for thyroid replacement drug therapy occur when it is used to treat obesity.
• Because of cardiac stimulation, use is contraindicated following an MI.
• Interactions for thyroid replacement drug therapy include binding agents, cholestyramine, antacids, antiseizure medications, and anticoagulants.
• Nursing implications includes assessing for drug allergies, contraindications, potential drug interactions and obtain baseline vital signs, weight.
• Cautious use is advised for those with cardiac disease, hypertension, and pregnant women.
• During pregnancy, treatment for hypothyroidism should continue.
• Fetal growth may be retarded if maternal hypothyroidism is untreated during pregnancy.
• Adjust dosage every 4 weeks to keep TSH at the lower end of the normal range.
• 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.
• 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.
• Teach patients the importance of alerting health care providers of thyroid medication use.
• Diabetic patients may need increased dosages of hypoglycemic meds which is stimulation of glucose.
• May decrease serum digoxin levels

Hyperthyroidism

• Is a condition of excessive thyroid hormones.
• Can be caused by Grave's disease, which is an autoimmune disease.
• Other causes are multinodular disease, Plummer's disease, and thyroid storm.
• Thyroid storm is induced by stress or infection and is severe and potentially life-threatening.
• Hyperthyroidism involves a sustained increase in synthesis and release of thyroid hormones by thyroid gland.
• It occurs more often in women and highest frequency in 20-40 yrs.
• Thyrotoxicosis is the physiologic effects/clinical syndrome of hypermetabolism resulting from increased circulating levels of T3 and/or T4
• Autoimmune disease of unknown origin leading to diffuse thyroid enlargement.
• Excessive thyroid hormone secretion (T3 and T4)
• Antibodies are developed to the TSH receptor.
• Leads to clinical manifestations of thyrotoxicosis.
• May progress to destruction of thyroid tissue resulting in hypothyroidism.
• Precipitating factors include insufficient iodine supply, infection, or stressful life events interacting with genetic factors.
• Accounts for 75% of cases of hyperthyroidism.
• Hyperthyroidism is related to effect of thyroid hormone excess.
• It leads to increased metabolism and tissue sensitivity to stimulation by sympathetic nervous system.
• There is an intolerance to heat.
• There is increased sensitivity to stimulant drugs.
• There is an elevated basal temperature.

Thyrotoxic Crisis

• Thyrotoxic crisis is involves excess amounts of thyroid hormones.
• It is an acute, rare condition, where all manifestations are heightened.
• It is a life-threatening emergency.
• Death is rare when treatment initiated.
• Presumed causes are additional stressors.
• Clinical manifestations of thyrotoxic crisis are tachycardia, heart failure, shock, hyperthermia, restlessness, agitation, seizures, abdominal pain, nausea, vomiting, diarrhea, delirium and coma.
• The treatment goal of thyrotoxic crisis is to decrease thyroid hormone levels and clinical manifestations with drug therapy.
• Therapy aims at managing respiratory distress, fever reduction, fluid replacement, and management of stressors.
• Radioactive iodine (I131) works by destroying the thyroid gland.
• This results in hypothyroidism, Lifelong thyroid hormone replacement will be needed.
• Surgery is used to remove all or part of the thyroid gland, requiring lifelong thyroid hormone replacement.
• Antithyroid drugs are thioamide derivatives which includes methimazole (Tapazole) and propylthiouracil (PTU).
• Betablockers are used for symptom management only, blocking sympathetic response.
• Methimazole (Tapazole) and propylthiouracil (PTU) are antithyroid drugs.
• Their mechanism of action is to inhibit the incorporation of iodine molecules into the amino acid tyrosine.
• Tyrosine is required to make T3 and T4.
• Its therapeutic uses are for Graves disease, to produce a euthyroid state prior to removal of thyroid, as an adjunct to irradiation of the thyroid gland and for emergency treatment of thyrotoxicosis.
• Adverse effects for anti-thyroid drugs are IRBC, and I WBC causing an inability to fight infection.
• May cause liver and bone marrow toxicity.
• Liver injury and hepatitis can occur.
• Over medication can result in symptoms of hypothyroidism.
• Contraindications for anti-thyroid drugs includes drug allergy.
• Nursing Considerations for anti-thyroid drugs include improvements taking 1-2 weeks before improvements
• Monitor vital signs, I&O, and weights when using anti-thyroid drugs.
• Take the medications at a consistent time each day with meals using anti-thyroid drugs.
• Don't discontinue anti-thyroid drugs abruptly.
• May be given a beta-blocker to decrease tremors and tachycardia with anti-thyroid drugs.
• Monitor for indications of hypothyroidism when using anti-thyroid drugs.
• Monitor CBC when using anti-thyroid drugs.