Thyroid Pharmacology Flashcards
What are the goals of thyroid hormone replacement therapy? What are three problems of using animal thyroid hormone in treating hypothyroidism?
Goals: 1 - Replace the function of thyroid gland. 2 - Prevent further growth of thyroid tissue. Problems: 1 - Contains T3 (acts rapidly, causes variable blood levels). 2 - Varies in potency. 3 - Allergies.
What is synthetic T4? MOA? Use & why? What is the half-life and time to peak therapeutic effect? Higher doses have to be given in? Side effects? In which patients should care be taken? This is not effective in what rare syndrome?
Synthetic T4: Levothyroxine sodium. MOA: This is converted to the more active T3 form in the liver (of course, T3 can then bind to TR and influence gene expression). Use: This is the drug of choice for hypothyroidism – it has a longer half-life than T3. Half-life: 6-7 days. Time to peak therapeutic effect: 3-4 weeks. Higher doses needed in infants and children. Side effects: hyperthyroidism (heart palpitations, nervousness, shaking, heat intolerance, weight loss, etc.). Be careful in patients with heart disease (angina pectoris, CAD, and elderly) – “start low, go slow.” Be careful in pregnancy. not effective in Chronic Fatigue Syndrome (difficulty converting T4 to T3).
What is synthetic T3? MOA? Use? Is this more potent than T4? Why is this less desirable in chronic replacement therapy than T4? Side effects? In which patients should care be taken?
Synthetic T3: Liothyronine sodium. MOA: T3 binds to TR complex in nucleus to influence gene expression. Use: Acute management of hypothyroidism in life-threatening hypothyroidism, myxedema coma. (IV formulation); This is 4X more potent than T4, but is less desirable because less stable, more costly, transient high levels. Side effects: hyperthyroidism (heart palpitations, nervousness, shaking, heat intolerance, weight loss, etc.). Be careful in patients with heart disease (angina pectoris, CAD, and elderly) – “start low, go slow.” Be careful in pregnancy.
How can iodine deficiency goiter be prevented?
Salt iodine supplement.
What are the treatment strategies for hyperthyroidism?
1 - Subtotal thyroidectomy (w/ T4 replacement). 2 - Irradiate thyroid gland w/ radioactive iodine131 (w/ T4 replacement). 3 - Inhibit Thyroid Peroxidase with antithyroid drugs (Propylhiouracil, Methimazole, Carbimazole. 4 - Interfere w/ thyroid hormone facilitation of sympathetic activity (B-blocker).
What is synthetic mix of T3/T4? Is this used much?
Liotrix (4:1 mix of T4:T3). Not used much.
What class is propylthiouracil? MOA? What class is methimazole? MOA? This is the active metabolite of what drug? These drugs are used for? Side effects? If patients develop side effects, what actions should be taken? Which drug has a longer half-life? Which drug is excreted slower? Which drug crosses the placenta to a greater extent? Which drug is more highly concentrated in breast milk? (And, as a conclusion, which drug is safer in pregnancy?) Which drug has a greater risk of agranulocytosis?
Thioamide (thyroid peroxidase inhibitors). MOA: Inhibit organification of iodide and coupling of iodotyrosine; also reduces peripheral deiodination of T4 to T3. Methimazole is also a thioamid. MOA: Inhibit organification of iodide and coupling of iodotyrosine; less effective in reducing peripheral deiodination of T4 to T3.
Use: Hyperthyroidism (oral); Thyrotoxicosis (per rectum, use at high dose). Rare side effects: hepatitis, agranulocytosis, lupus-like syndrome. Discontinue and use radio-iodine if patient develops agranulocytosis or drug-induced lupus. Methimazole: Longer half-life, slower excretion, more transplacental passage, greater concentration in breast milk, (as such, Propylthiouracil is the preferred drug in pregnancy). A greater risk of agranulocytosis is seen in propylthiouracil.
Radioactive iodine is the treatment of choice for what thyroid condition? It is also used for? MOA? Side effects? Contraindications? Does this increase the risk of cancer? How is this taken? What is the half-life? How long will it take to have effects?
Treatment of choice for hyperthyroidism
after antithyroid drug therapy. Also used for: ablation after cancer. MOA: Radioactive agent that emits beta particles and gamma rays that destroy thyroid cells. Side effects: Possible permanent or transient hypothyroidism, Contraindicated in pregnancy, breast-feeding, and generally not considered initial treatment for children (
When can B-blockers be used in treating thyroid conditions?
B-Blockers (propanolol, metoprolol, atenolol, nadolol) can be used for symptomatic treatment of hyperthyroid conditions, esp in Grave’s. No effect on synthesis or secretion of thyroid hormone. Should not be used unless symptoms are moderate or severe and should be discontinued when patient returns to euthyroid.
