Pharmacology Chapter 58: Drugs for thyroid disorders
Agranulocytosis
A life-threatening drop in white blood cells. The most serious adverse effect of methimazole.
Dosage and administration of Iodine
1. Admin in capsules or oral liquid 2. The goal is to reduce thyroid hormone production w/o causing destruction of thyroid tissue 3. Dosage for Graves dz = 4-10 mCi
Liothyronine (T3)
-Cytomel, Triostat -Nursing implications for liothyronine are the same as those for levothyroxine - Success indicated by resolution of S&S of hypothyroidism and normal T3 and TSH - T4 levels cannot be used to evaluate therapy
Four indications for using Methimazole to treat thyroid disorder
1. Reduction of thyroid hormone production in Graves disease 2. Control of hyperthyroidism until the effects of radiation on the thyroid become manifest 3. Suppression of thyroid hormone production before subtotal thyroidectomy 4. Treatment of thyrotoxic crisis
What are the three principal actions of thyroid hormones?
1. Stimulation of energy use 2. Stimulation of the heart 3. Promotion of growth and development
How is Graves disease treated?
1. Surgical removal of thyroid tissue, 2. Destruction of thyroid with radioactive iodine 3. Suppression of thyroid hormone synthesis
Hormonal regulation of thyroid function occurs as follows:
1. TSH from the hypothalamus causes the pituitary to release TSH which causes the thyroid to make and release T3 and T4. which then anti on the pituitary to suppress further release of TSH
Levothyroxine (T4) administration education
1. Take on empty stomach in the AM at least 30-60min before food. 2. Therapy is life long, do not d/c without consulting prescriber
How long does it take for the full effects of Iodine to develop?
2-3 month
How long will it take for the full benefits of Methimazole to develop?
3-12 weeks
Lugol's solution administration education
Advise patients to dilute strong iodine solution with fruit juice or another beverage to increase palatability
Adverse of effects of methimazole
Agranulocytosis Hypothyroidism Effects of pregnancy - neonatal hypothyroidism, goiter, congenital hypothyroidism
How should body wastes from patients taking high dose radioactive iodine be handled?
As hazard waste
Drugs that can significantly reduce levothyroxine absorption
Cholestyramine (Questran) Colestipol ( Colestid) Sucralfate (Carafate) H2 receptor blockers Proton pump inhibitors Aluminum containing antacids Iron supplements Calcium supplements
What is a major cause of hyperthyroidism in iodine sufficient countries ?
Chronic autoimmune thyroiditis (Hashimoto's thyroiditis)
Evaluation of therapeutic effects of levothyroxine in Children
Clinical evaluation should reveal 1. normalization of intellectual function, growth and development. 2. Only measurements of height provide a good index of thyroid sufficiency. 3. Tests show normal levels of TSH and T4
Evaluation of therapeutic effects levothyroxine in Adults
Clinical evaluation should reveal 1. reversal of signs of thyroid deficiency 2. an absence of signs of thyroid excess -tachycardia 3. Tests indicating normal plasma TSH and T4
High risk patients with radioactive iodine?
Contraindicated during pregnancy and lactation
Severe toxicity from Lugols strong iodine solution
Corrosive injury to the Gi Tract Treatment includes gastric lavage and giving sodium thiosulfate
Levothyroxine (synthetic T4)
Drug of choice for most patients who require thyroid hormone replacement
When is Iodine-121 contraindicated?
During pregnancy and lactation
Maternial hypothyroidism
During the first trimester of pregnancy can result in permanent neuropsychological deficits in the child
What will chronic overtreatment with levothyroxine cause?
Especially in older adults Atrial fibrillation Bone loss
Drugs that reduce Levothyroxine absorption
H2 receptor blockers Proton pump inhibitors Cholestyramine, Colestipol, Sucralfate, Orlistat Aluminum containing antacids Calcium supplements Magnesium salts, Separate admin. of levothyroxine and these drugs by 4 hours.
Adverse effects of iodine use for thyroid cancer
High doses ( 50 - 150 mCi) can cause radiation sickness, leukemia, and bone marrow depression.
Strong iodine solution (Lugol's solution)
Nonradioactive iodine Treats hyperthyroidism by reducing iodine uptake, reducing TH production, blocking release of TH
What can result from excessive thyroid destruction
Hypothyroidism
In what situations if levothyroxine given IV
IV reserved for treating myxedema coma and patient who cannot take levothyroxine orally.
Methimazole administration education
Instruct the patient to take methimazole once daily, at the same time every day.
What happens to most of the T4 that is released from the thyroid?
It is converted to T3 in the periphery.
Drugs for Hypothyroidism (thyroid hormone replacement)
Levothyroxine (T4)
drugs for hyperthyroidism
Methimazole (Tapazole) Propylthiouracil (PTU)
Pregnancy cautions with Methimazole treatment
Methimazole should be avoided during the first trimester of pregnancy. It is on the NIOSH hazard drug list and should be handled with caution by healthcare workers of childbearing age.
Are diagnostic doses of Iodine-133 harmful?
No, less than 10 mCi to diagnose hyperthyroidism, hypothyroidism and goiter.
Drug used to suppress thyroid function before thyroidectomy.
Non-radioactive iodine: Lugol's solution
When are Beta Blockers used to treat symptoms associated with thyroid disorders
Propranolol: Can suppress tachycardia and other symptoms of Graves' disease Benefits derive from beta-adrenergic blockade, not from reducing levels of T3or T4 Beneficial in thyrotoxic crisis
Drugs for Graves disease and thyroid cancer
Radioactive Iodine (131-I)
Therapeutic goal of levothyroxine (T4) administration
Resolution of signs and symptoms of hypothyroidism and restoration of normal laboratory values for serum TSH and free T4.
How long will it take for therapeutic effects of iodine therapy to fully develop?
Responses take 2-3 months Methimazole or propythiouracil may be required during the interval.
Baseline data needed before administration of levothyroxine.
Serum TSH and free T4
Baseline data needed before starting therapy with Methimazole
Serum free T3 and free T4
What is the therapeutic goal of radioactive iodine ?
Suppression of thyroid hormone production
Therapeutic goal of Strong Iodine Solution (Lugol's Solution)
Suppression of thyroid hormone production in preparation for subtotal thyroidectomy Also used to suppress thyroid hormone release in patients experiencing thyroid storm.
Daily recommendations for taking Levothyroxine
Take on an empty stomach in the morning, at least 30-60 minutes before eating.
What is the most sensitive way to diagnose hypothyroidism?
Testing serum for elevated levels of TSH
What patients should avoid taking Methimazole?
This in their first trimester of pregnancy
Adverse effects of chronic treatment with levothyroxine
Thyrotoxicosis Atrial Fibrillation Bone Loss- Fractures
The thyroid gland produces what two active hormones?
Triiodothyronin (T3) Thyroxin (T4 tetraiodothyronine)
Levothyroxine can intensify the effects of what anticoagulant?
Warfarin
Drugs that accelerate levothyroxine metabolism
Warfarin ( dose may need to be decreased) Catecholamines - thyroid hormones sensitize the heart to catecholamines ( epinephrine, dopamine, dobutamine) and may promote dysrhythmias.
What S&S should be monitored to evaluate successful treatment by methimazole?
Weight gain Decreased HR Other indications that levels of thyroid hormones have declined Lab tests should indicate a decreased free T3 & T4
Goiter
an enlargement of the thyroid gland
methimazole, propylthiouracil
antithyroid agents (hyperthyroidism) suppress thyroid hormone synthesis
S&S of adverse effects of Iodism from iodine toxicity
brassy taste burning sensations in the mouth soreness of gums and teeth discontinue treatment and notify prescriber if this occurs.
thyrotoxicosis
condition caused by excessive thyroid hormones S&S : Tachycardia, Angina, Tremor, Nervousness, Insomnia, Hyperthermia, Heat intolerance, Sweating notify prescriber if S&S develop
Graves disease
hyperthyroidism with toxic goiter Most common cause of excessive thyroid hormone secretion
Hypothyroidism almost always requires what duration of therapy
lifelong replacement therapy with thyroid hormones
The nurse instructs a patient about taking levothyroxine [Synthroid]. Which statement by the patient indicates the teaching has been effective? A."To prevent an upset stomach, I will take the drug with food." B."If I have chest pain or insomnia, I should call my doctor." C."This medication can be taken with an antacid." D. "The drug should be taken before I go to bed at night."
•Answer: B •Rationale: Levothyroxine overdose may produce the following symptoms: tachycardia, angina, tremor, nervousness, insomnia, hyperthermia, heat intolerance, and sweating; the patient should contact the prescriber if these symptoms are noted. Levothyroxine should be taken in the morning on an empty stomach 30 minutes before a meal. Levothyroxine should not be taken with antacids, which reduce the absorption of levothyroxine.
The nurse instructs a patient in the administration of Lugol's solution. The nurse determines that teaching has been effective if the patient makes which statement? A."I'll need to take this solution for the rest of my life." B."The medication should be diluted in fruit juice." C."To prevent stains on my teeth, I'll use a straw." D."The solution should be placed under my tongue."
•Answer: B •Rationale: Lugol's solution is administered in a dosage of drops and should be mixed with juice or some other beverage to mask its unpleasant taste. Lugol's solution is used for a short time (usually less than 10 days) to suppress thyroid function in preparation for thyroidectomy or during a thyrotoxic crisis. Lugol's solution does not stain teeth. The solution should not be placed under the tongue.
A patient takes levothyroxine [Synthroid] 0.75 mcg every day. It is most appropriate for the nurse to monitor which laboratory test to determine whether a dose adjustment is needed? A.Thyrotropin-releasing hormone (TRH) B.Thyroid-stimulating hormone (TSH) C.Serum free T4test D. Serum iodine level
•Answer: B •Rationale: Serum thyroid-stimulating hormone (TSH) is the preferred laboratory test for monitoring replacement therapy in patients with hypothyroidism.
A patient with hyperthyroidism is taking propylthiouracil (PTU). It is most important for the nurse to assess the patient for which adverse effects? A.Gingival hyperplasia and dysphagia B.Dyspnea and a dry cough C.Blurred vision and nystagmus D. Fever and sore throat
•Answer: D Rationale: Agranulocytosis is the most serious toxicity for patients taking PTU. Sore throat and fever may be the earliest indications.