Thyroid & Antithyroid Drugs – NURS1059 (2024-2025)

Question-and-Answer flashcards covering thyroid and antithyroid pharmacology, mechanisms, adverse effects, nursing considerations, and drug interactions.

What is the lifelong goal of therapy in hypothyroidism?

Provide adequate thyroid hormone replacement to compensate for deficient endogenous production.

Which drug is considered the preferred treatment for hypothyroidism?

Levothyroxine (Thyroxine®, Synthroid®, Eltroxin®).

Why is levothyroxine the drug of choice for hypothyroidism?

It has a long duration of action (2–3 weeks), predictable serum levels, and can be dosed once daily.

What thyroid hormone does levothyroxine mimic?

Synthetic T4 (thyroxine).

How protein-bound is levothyroxine in the bloodstream?

Approximately 99 % protein-bound.

How often is levothyroxine usually administered?

Once daily, preferably in the morning on an empty stomach.

What is liothyronine (Cytomel®) and when is it used cautiously?

Synthetic T3; used cautiously in patients with pre-existing heart disease because it is more potent and cardiotoxic.

What combination of hormones does liotrix (Thyrolar®) contain?

Both T3 and T4.

What are the common dose-related adverse effects of thyroid hormone replacement?

Signs of hyperthyroidism such as tachycardia, chest pain, insomnia, and nervousness.

List three contraindications for thyroid hormone replacement.

Allergy, recent myocardial infarction, and adrenal insufficiency (also contraindicated in untreated hyperthyroidism).

At what adult resting pulse rate should levothyroxine be withheld and the prescriber notified?

100 beats/min.

Why must levothyroxine doses often be adjusted during pregnancy?

To meet increased maternal and fetal needs and prevent cretinism.

Name three drug classes whose efficacy is reduced by thyroid replacement therapy.

Digoxin, insulin, and oral hypoglycemic agents for type 2 diabetes.

Which common over-the-counter products should be avoided within 2 hours of levothyroxine?

Antacids and iron supplements.

State two teaching points about missed doses of levothyroxine.

Do not double up; if two consecutive doses are missed, notify the prescriber.

What is the primary therapeutic goal in treating hyperthyroidism?

Reduce thyroid hormone production to normal levels and relieve symptoms.

Which antithyroid drug blocks iodine incorporation into thyroid hormone and is used pre-op or in thyroid storm?

Propylthiouracil (PTU).

Why does PTU take days to weeks to produce therapeutic effects?

It only inhibits new hormone synthesis and does not affect circulating or stored hormone.

What serious fetal risks are associated with PTU and methimazole?

They can cross the placenta and cause fetal goiter or cretinism.

Which antithyroid medication is preferred because of milder adverse effects and once-daily dosing?

Methimazole (Tapazole®).

What short-term iodine preparation shrinks the thyroid pre-surgery and treats thyroid storm?

Lugol’s Solution (strong iodine solution).

Explain the mechanism of action of radioactive sodium iodide-131 (Na I¹³¹).

It is taken up by thyroid tissue and emits beta radiation that destroys thyroid follicles (ablation).

List two major adverse events associated with Na I¹³¹ therapy.

Liver toxicity and bone marrow suppression.

What isolation precautions are required for patients receiving Na I¹³¹?

Radiation isolation with protective measures for staff and visitors.

How does potassium perchlorate act as an antithyroid agent?

It concentrates in the thyroid and blocks iodine uptake, decreasing hormone production.

Why are beta-adrenergic blockers used in hyperthyroidism?

To alleviate systemic symptoms such as tachycardia, tremors, anxiety, and hypertension; they do not affect hormone levels.

Which beta blocker also inhibits peripheral conversion of T4 to T3?

Propranolol.

Identify two nursing assessments essential during thyroid replacement therapy.

Monitor apical pulse/BP and watch for signs of hyperthyroidism.

What laboratory tests are routinely monitored during thyroid replacement initiation?

TSH and circulating thyroid hormone levels every 6–8 weeks until stable, then at least annually.

Why should patients avoid switching brands of levothyroxine?

Bioavailability can vary among brands, leading to under- or over-replacement.