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23 Cards in this Set
- Front
- Back
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Thyroid hormone mechanism
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Free thyroid hormone enters the cell where T4 is converted to T3 by 5'-deiodinase. T3 enters the nucleus where it leads to increased formation of RNA and protein synthesis.
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Levothyroxine in a nutshell
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T4
Stable, low-cost, once-daily administration |
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Liothyronine in a nutshell
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T3
Potent, expensive, multiple-daily administrations Increased risk of cardiotoxicity |
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What is Liotrix?
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4:1 ratio of T4:T3
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Thyroid administration
Side effects |
Kids - restlessness / insomnia
Adults - heat intolerance, arrhythmias Elderly - A-fib, accelerated osteoporosis |
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Myxedema & CAD
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If surgery is indicated, it should be done prior to thyroid replacement
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Myxedema coma
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Intubation
Loading dose of levothyroxine |
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Hypothyroidism & pregnancy
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Levothyroxine administration important since fetal brain depends on maternal thyroxine
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What are thioamides?
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Propylthiouracil
Methimazole |
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Thioamides
Mechanism of action |
Prevents hormone synthesis by inhibiting thyroid peroxidase-catalyzed reactions
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Propylthiouracil
Special characteristics |
Inhibits peripheral conversion (via 5'-deiodinase) of T4-T3
(Preferred treatment in thyroid storm) |
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Methimazole
Special characteristics |
Easily crosses the placenta
10x more potent than propylthiouracil |
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Propylthiouracil
Side effects |
Agranulocytosis
Hepatotoxicity |
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Methimazole
Side effect |
Agranulocytosis
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2 anion inhibitors
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Perchlorate (ClO4-)
Thiocyanate (SCN-) |
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Anion inhibitors
Mechanism of action |
Block uptake of iodide by the thyroid through competitive inhibition
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Anion inhibitors
Side effect |
Aplastic anemia
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Potassium iodide
Mechanism of action |
Inhibits hormone release by inhibiting thyroglobulin proteolysis, known as the Wolff-Chaikoff effect.
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Radioactive Iodine
Contraindications |
Pregnant and nursing women
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Propranolol
Side effects |
Depression
Claudication Bronchospasm CHF Masks hypoglycemic symptoms in diabetics |
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Ipodate
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Radiocontrast agent
Inhibits 5'-deiodinase Contains large amounts of iodine which inhibits thyroid gland by the Wolff-Chaikoff effect. |
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Amiodarone
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Antiarrhythmic drug
Inhibits 5'-deiodinase Structurally similar to TSH, may cause hyperthyroidism Contains large amounts of iodine which inhibits thyroid gland by the Wolff-Chaikoff effect. |
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Thyrotropin alpha
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Stimulates release of thyroglobulin from the thyroid. High thyroglobulin levels is indicative of thyroid cancer.
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