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Medicine

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Endocrine

Question
2 out of 18
 

Which of the following drug inhibit conversion of T4 to T3? (AIIMS May 2011)



A Carbimazole
B Propranolol

C Amiodarone
D All of the above

Ans. B

Thyroid function tests (TFTs)

Physiology:

1. The thyroid produces mainly T4, (inactive), & little amount of T3 (Active).

2. 85% of T3 is formed from peripheral conversion of T4

Drugs which inhibit peripheral conversion of T4 to T3 (FAQ)

1). Propranolol

2). Dexamethasone

3). Propylthiouracil

4). High dose of iodine

5). Radiographic contrast media

Extra Edge: All these drugs are used in hyperthyroid crisis (MCQ)

Extra Edge:

1). Most of T3 and T4 in plasma is protein bound, mainly to thyroxine-binding globulin (TBG). The unbound portion is the active part.

2). T4 and T3 increase cell metabolism, via nuclear receptors, and are thus vital for growth and mental development

3). They also catecholamine effects.

Extra Edge:

1). If we give high dose of iodine for short period it inhibit T4 synthesis (Wolf Chaikoff effect)

2). If we give low dose of iodine for a long period it increases T4 synthesis (Job Basedow effect)

Endocrine Flashcard List

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