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318 CH 57
Drugs for Thyroid dysfunction
| Question | Answer |
|---|---|
| What are the 2 classes of drugs for hyperthyroidism? | Antithyroid drugs: Thionamides. Radioactive iodine |
| What do Thionamides do? | suppress thyroid hormone synthesis. |
| What are the 2 Thionamides? | Propylthiouracil (PTU) and Methimazole [Tapazole] |
| PTU differs from methimazole in 2 major ways, what are they? | shorter half-life and it poorly crosses placenta (preferred in pregnancy) |
| what is the mechanism of action for Propylthiouracil (PTU) | blocks thyroid hormone synthesis in 2 ways: (1) PTU prevents the oxidation of iodine, thereby inhibiting the incorporation of iodine into thyrosine. (2) PTU prevents iodinated tyrosines from coupling |
| How long does it take for Propylthiouracil (PTU) to reach a euthyroid state? why?: | PTU does NOT destroy existing stores of thyroid hormone, therefore it may take 3-12 weeks to produce euthyroid |
| how is Propylthiouracil (PTU) administered? | Orally |
| how long does it take to see the therapeutic action of propylthiouracil (PTU) | 30 minutes |
| what is Propylthiouracil (PTU) used for? | hyperthyroidism |
| what are the adverse effects of propylthiouracil (PTU) | agranulocytosis, hypothyroidism |
| which of the antihyperthyroidism drugs is preferred in pregnancy/lactation? | PTU |
| PTU and Methimazole [Tapazole] are very similar, in what ways are they different? | Methimazole [Tapazole] has a longer half-lief (1x/day), it does not block conversion of T4 into T3 in the periph (slower onset), crosses placenta more readily than PTU and has a higher concentration in breast milk. |
| which between PTU and Methimazole [Tapazole] is preferred? | in pregnancy, PTU. otherwise Methimazole [Tapazole] is preferred because it has 1x/day dosing. |
| what is iodotope? | radioactive iodine used in hyperthyroidism. |
| how long does it take for the effects of idotope to become aparent? how long for it to reach full effects? | effects are aparent in a few days/weeks and full effects are apparent in 2-3 months. |
| what is a common complaint by pts on iodotope? | hypothyroidism |
| what is used to treat hypothyrodism? | Levothyroxine (T4) [Synthroid] |
| what is the mechanism of action in Levothyroxine? | Levothyroxine is identical to Human T4. it is converted to T3 just like normal T4 and thus produces normal levels of BOTH T3 and T4. |
| what is Levothyroxine used for | hypothyroidism |
| adverse effects of levothyroxine: | Acute overdose (thyrotoxicosis). Chronic overdose (accelerated bone loss and increased fisk for A.fib) |
| what are some drugs that decrease the absorption of levothyroxine? | Questran, Colestid, Calcium supplements(TUMS), Carafate, albuminum-containing antacids (Maalox, Mylanta) and iron supplements |
| how far should you separate the administration of levothyroxine and drugs that reduce its absorption? | by 4 hours |
| what are some drugs that accelerate the metabolism of levothyroxine? | Dilantin, Tegretol, Rifadin, Zoloft, Phenobarbital |
| How to levothyroxine and Warfarin interact? | warfarin effects are enhanced |
| how do levothyroxine and catecholamines interact? | there is an increased risk for catecholamine-induced dysrhythmias |
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