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.