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Old 11-19-2010
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Thyroid Step 1 practice Qnz - 4

Q NO 216: A leak of radioactive material occurs at a plant that handles the disposal of such waste. A number of workers are believed to have been exposed to this material which contains heavy isotopes. Which of the following should be immediately administered to prevent tissue damage in these individuals?


A. Propylthiouracil
B. Potassium iodide
C. Propranolol
D. Prednisone
E. L-thyroxine


??? explanation?
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Old 11-19-2010
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option B-potassium iodide.
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Old 11-19-2010
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Originally Posted by faith View Post
option B-potassium iodide.
Very impressive. Could you explain to me why potassium iodide is the best tx?

Thx
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Old 11-19-2010
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The first step in the formation of thyroid hormone is energy-dependent transport of inorganic iodide into the thyroid follicular cell. This process is called iodide trapping and is accomplished by the sodium iodide symporter (NIS) located at the basolateral membrane of the thyroid follicular cell.

The thyroid follicular cells also take up other ions such as perchlorate and pertechnetate and even radioactive iodine—all through the NIS. Since all three types of chemicals—inorganic iodide, other ions, and radioactive iodine—use the same transporter, each competitively inhibits the other. That is, high levels of any one substance will significantly reduce the uptake of the others.

Physicians can use this principle by administering potassium iodide to a person exposed to radioactive isotopes of iodine. By competitive inhibition, less radioactive material will enter the thyroid, which will significantly reduce the amount of tissue damage.
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Old 11-19-2010
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Quote:
Originally Posted by aktorque View Post
Very impressive. Could you explain to me why potassium iodide is the best tx?

Thx
i don't know where i had read in my prep but concept was something like- in case of any heavy metal poisoning we have to give a chelating agent or an ion so that it will bind to the heavy metal and prevent the binding of heavy metal to our tissue proteins.of all the options given only potassium iodide had a free ion to donate..so i sort of ruled out other options..
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Old 11-19-2010
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In this instance though, you're using potassium iodide (KI) because you want to keep the non-radioactive iodide in the thyroid and not the radioactive one. See the thyroid is the only place in the body that uses Iodide so if you give a high level of regular KI then it will competitively force the radioactive iodide in the body from the radiation to exit the body without being incorporated in the tissue. I know what you meant about chelating agents but that is not what they are asking here.
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Endocrine-, Physiology-, Step-1-Questions, Toxicology-

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