Pharm Test 3 Thyroid and Anti-Thyroid Flashcards
Thyroxine -T4
Triiodothyronine - T3
Most T3 form from deiodination of T4 inthe peripheral tissues. T3 has a greater affinity for receptors and is 10x more potent.
MOA: TRH (IP3)->TSH(cAMP)->T3/T4 (nuclear receptor)->altered gene expression
Effects: Increase BMR via Na/K atpase activity-> increased RR, temp and o2 consumption. Potentiates effects of catecholamines -> increases sympathetic activity (increase CO and HR). promotes brain/CNS development
Used in TX of cretinism and myxedema
AE: Tremors, Tachycardia, arrhythmia, Heat intolerance
***only free forms are active, t3/4 circulate bound to TBG-> decrease in hepatic failure; increase by pregnancy and estrogen intake
Propylthiouracil (PTU)
Methimazole
Thiomides: slow onset of action b/c they don’t inhibit previously made T3/4
MOA: inhibit peroxidase-> block iodination of TG and inhinit coupling reactions
Effects: PTU can also inhibit 5’ deiodinase decreasing the converstion of T4->T3
DOC for thyroid storm ->PTU
AE: PTU-> rash, agranulocytosis, aplastic anemia, hepatotoxicity, and vasculitis
Serious AE are less common with methimazole but it is a teratogen
***Goitrogens-may cause goiter. PTU is safe in pregnanct
Iodide
Iodine
High levels of iodide paradoxically inhibit thyroid hormone syntheses –> Wolff-Chaikoff Effect (lasts 2 weeks)
MOA: Decreased organification and release or thyroid hormones
Effect: Decrease vascularity and size of the thyroid -> useful preoperatively. Can treat thyrotoxicosis in conjunction with PTU and B Blockers
AE: increase size of parotid and maxillary gland, anaphylactoid reaction/angioedema, Brassy taste, burning of teeth/gums
**Lugol’s solution -> Iodine + KI
I131
Radioactive iodine is taken up and sequestered in the thyroid.
MOA: Beta particles damage tissue. Does NOT cause cancer
Effect: Tx of hyperthyroidism and grave’s that is refractory to other therapy
AE: May develop hypothyroidism, CI in pregnant and nursing mothers
**Dosing is difficult. Permanent reduction of activity
Propranolol
Esmolol
B blocker
MOA: control CVS sxs, tremors and sweating associated with thyroid storm
Effect: Propranolol -> prevents conversion of T4 to T3 and Esmolol is used intraoperatively
Diatrizoate
Iohexol
Radiocontrast Media
MOA: inhibt 5’ deiodinase
Effect: Rapidly reduces T3 concentration in thyrotoxicosis
**May also inhibt hormone release from thyroid gland
Perchlorate
Thiocyanate
Pertechnetate
Inhibit concentration of iodine in the gland by blocking transportation
MOA: Competatively inhibits the Na/I symporter
AE: aplastic anemia
Glucocorticoids
Inhibits peripheral conversion of T4 to T3
**PTU and NaI can also block conversion of T4->T3
Propylthiouracil
Methimazole
Thiomides: slow onset of action b/c they don’t inhibit previously made T3/4
MOA: inhibit peroxidase-> block iodination of TG and inhinit coupling reactions
Effects: PTU can also inhibit 5’ deiodinase decreasing the converstion of T4->T3
Interesting hypothyroidism
Cabbage (contains thiocyanate)
Cassava (Carbs and thiocyanate)
Iodide
Iodine
High levels of iodide paradoxically inhibit thyroid hormone syntheses –> Wolff-Chaikoff Effect (lasts 2 weeks)
I131
Radioactive iodine is taken up and sequestered in the thyroid
Propranolol
Esmolol
B blocker
Diatrizoate
Iohexol
Radiocontrast Media
Perchlorate
Thiocyanate
Pertechnetate
Inhibit concentration of iodine in the gland by blocking transportation
