Week 5 Antithyroid Flashcards
(19 cards)
What are antithyroid agents used for?
Management of hyperthyroidism, particularly Graves’ disease
Antithyroid agents include thionamides, potassium iodide, and radioactive iodine.
Name the thionamides used in hyperthyroid management.
- Methimazole
- Propylthiouracil (PTU)
Thionamides are the preferred choice for hyperthyroid management.
How do thionamides work?
By blocking thyroid hormone synthesis
PTU also blocks the conversion of T4 to T3.
Which thionamide is preferred during the first trimester of pregnancy?
Propylthiouracil (PTU)
PTU less readily crosses the placenta compared to methimazole.
What is the main action of potassium iodide?
Inhibiting thyroid hormone release
Potassium iodide is often used as pretreatment before thyroid surgery.
What does radioactive iodine do?
Causes damage to thyroid tissue, reducing thyroid function
This treatment is definitive and occurs over 6–18 weeks.
What hormone levels are affected by hyperthyroidism?
Increased levels of triiodothyronine (T3) and thyroxine (T4)
This results in decreased production of thyroid-stimulating hormone (TSH) by the pituitary gland.
What are the pharmacodynamics of thionamides?
Inhibit thyroid hormone synthesis by blocking:
* Thyroid peroxidase (TPO) reactions
* Iodine organification
They do not block the release of preformed hormones.
What are the adverse effects of thionamides?
- Agranulocytosis
- Hepatotoxicity
- Aplastic anemia
- ANCA-positive vasculitis
- Dermatologic reactions
- Lupus-like syndrome
Severe side effects are rare but can occur.
What are the indications for iodides?
- Pretreatment before thyroid surgery
- Adjunctive therapy for hyperthyroidism
- Thyroid storm
- Prophylaxis for radioactive iodine exposure
Iodides can reduce the size of a hyperplastic thyroid gland.
What are the contraindications for using iodides?
- Pregnancy
- Allergy to iodine
- Renal failure
Iodides can cause fetal hypothyroidism and goiter.
What is a major adverse effect of radioactive iodine?
Permanent hypothyroidism
This occurs due to destruction of too much thyroid tissue.
What are the drug interactions associated with thionamides?
- May increase myelosuppressive effect of clozapine and promazine
- Decrease radioactive iodine effect
- Decrease anticoagulant effect of warfarin
These interactions can complicate treatment.
Fill in the blank: Methimazole is the preferred drug for _______.
nonpregnant individuals
Methimazole has a longer half-life compared to PTU.
What are the pharmacokinetics of propylthiouracil?
- Absorption: rapid
- Distribution: accumulates in the thyroid gland
- Protein-bound: 80%–85%
- Metabolized in the liver
- Excreted in the urine
PTU crosses the placenta less readily than methimazole.
What precautions should be taken with radioactive iodine?
Radiation precautions to reduce exposure to close contacts
This is important to ensure safety for others.
True or False: Radioactive iodine is contraindicated in pregnant or breastfeeding individuals.
True
It can destroy the fetal or infant thyroid gland.
What is a common side effect of potassium iodide?
GI intolerance
It may also cause esophageal or mucosal injury.
What can exacerbate hyperthyroidism symptoms when using iodides?
Iodides themselves
They should be used in conjunction with other therapies.
