Thyroid drugs Flashcards
(40 cards)
What are the three approaches to treatment of hyperthyroidism
Interfere with thyroid hormone production
Modify tissue response to thyroid hormone
Destroy thyroid gland via radiation or surgery
Name the nine classes of drugs used to tx hyperthyroidism
Iodide uptake inhibitors (anion inhibitors) Inorganic Iodide Radioactive Iodine Thioamides Beta-adrenergic Antagonists Radiocontrast agents Corticosteroids Lithium Amiodarone
Name the three Iodide uptake inhibitors and its MOA
Thiocyanate
Perchlorate
Pertechnetate
- competes with iodid for uptake into the thyroid gland follicular cells
- causes aplastic anemia, so use is limited
Name the inorganic iodide used to treat hyperthyroidism and it’s MOA
Lugol’s solution
MOA is to cause Wolff-Chaikoff effect (high concentration of iodide inhibits T4/T3 synthesis/release via negative feedback loop)
Lugol’s solution works in three ways by
inhibiting iodide organification (oxidation)
inhibiting release of thyroid hormones
decreasing the size and vascularity of enlarged thyroid gland for easier surgical excision
In order for the autoregulatory phenomenon of Wolff-Chaikoff effect to work, what pathway must be intact
negative feedback loop
*usually the case thyroid dysfunction not previously treated
What are the five disadvantages of administering Lugol’s solution
Increases the intraglandular stores of iodine
- delays onset of thionamide therapy
- delays radioactive treatment
Must be used with other therapies
-gland can “escape” from iodide block to produce severe thyrotoxicosis
Crosses placenta
- can cause fetal goiter in large doses adminisitered over prolonged times
- avoid in pregnancy
Irritating and destructive to mucosa
Causes Jod-Basedow phenomenon
What is the Jod-Basedow phenomenon
Hyperthyroidism following administration of iodine or iodide which could lead to thyrotoicosis in people who have thryoid abnormalities that cause the gland to function without the control of the pituitary.
*The Jod-Basedow effect does not occur in persons with normal thyroid glands who ingest extra iodine in any form.
What is the difference between Wolff-Chaikoff effect and Jod-Basedow phenomenon
some ways the Jod-Basedow phenomenon is the opposite of the Wolff-Chaikoff effect, which refers to the short period of thyroid-hormone suppression which happens in normal persons and in persons with thyroid disease, when comparatively large quantities of iodine or iodide are ingested. However, unlike the Wolff-Chaikoff effect, the Jod-Basedow effect does not occur in persons with normal thyroid glands, as thyroid hormone synthesis and release in normal persons is controlled by pituitary TSH secretion, which does not allow hyperhyroidism when extra iodine is ingested.
Radioactive Iodine is used to treat
thyrotoxicosis
Radioactive iodine’s MOA includes
Rapid absorption and concentration by the thyroid, and incorporation into storage follicles
*the thyroid tissue is destroyed within a few weeks
What is the goal of radioactive iodine
to administer enough to result in Euthyroid state without precipitating hypothyroidism
Radioactive iodine can only be used in adults of what age
> 35 years of age
Radioactive iodine is not used in which patient population
pregnant or nursing mothers
The incidence of hypothyroidism after 2 years and 10 years of therapy include
after 2 years up to 30%
after 10 years up to 50%
Name the two thioamides used to treat hyperthyroidism
Prophylthiouracil (PTU)
Methimazole (Tapazole)
What is the MOA of the PTU and Methimazole
Binds to thyroid-peroxidase thereby inhibiting iodine organification and synthesis of thyroid hormones
prevents coupling of iodotyrosines (DIT)
What additional MOA does PTU have that Methimazole lacks
PTU also inhibits the peripheral conversion of T4 to T3, unlike methimaxole
Name four other drugs whose MOA is similar to PTU (inhibition of T4 to T3)
Sodium Thiopental (induction agent)
Propanolol (beta adrenergic antagonist)
Mifepristone (steroid receptor antagonist used to tx cushing’s syndrome)
Sodium Ipodate (radiocontrast agent used in ERCP procedures)
Does the thioamides (PTU/Mehtimazole) inhibit the release of stored thyroid hormones
NO
What is the major SE associated with PTU/Methimazole administration
Pruritic rash with fever
What is the most life-threatening SE associated with PTU/Methimazole adminsistraton
Severe agranulocytosis (lowered WBC) bleeding tendancies
PTU/Methimazole and pregnacy
Both drugs cross the placenta and will effect the fetal thyroid
- however, PTU is preferred bc it is more highly protein bound and crosses placental less
- Okay to breast feed
Thioamides are sometimes referred to as?
Goitrogen
*as TSH levels rise in response to lowered thyroid hormone levels, the thyroid gland hypertrophies
