Propylthiouracil is preferred over Methimazole in treatment of Thyroid storm because
**Core Concept**
Thyroid storm is a life-threatening complication of untreated or inadequately treated hyperthyroidism, characterized by severe hypermetabolism, tachycardia, and alterations in mental status. Propylthiouracil and methimazole are both antithyroid medications used to treat hyperthyroidism, but they have different mechanisms of action and side effect profiles.
**Why the Correct Answer is Right**
Propylthiouracil is preferred over methimazole in the treatment of thyroid storm because it has additional properties that make it more suitable for this condition. Propylthiouracil inhibits the peripheral conversion of T4 to T3, which is a critical step in the pathogenesis of thyroid storm. This action helps to reduce the production of the more potent thyroid hormone T3, which is responsible for the severe symptoms of thyroid storm. Additionally, propylthiouracil has a lower risk of inducing agranulocytosis, a potentially life-threatening side effect of methimazole.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while propylthiouracil may have a slower onset of action compared to methimazole, this is not the primary reason for its preference in thyroid storm.
**Option B:** This option is incorrect because there is no evidence to suggest that propylthiouracil has a more favorable effect on thyroid hormone binding proteins than methimazole.
**Option C:** This option is incorrect because while propylthiouracil may have a lower risk of hepatotoxicity compared to methimazole, this is not the primary reason for its preference in thyroid storm.
**Clinical Pearl / High-Yield Fact**
The use of propylthiouracil in thyroid storm is a classic exam trap, as many students may be tempted to choose methimazole due to its faster onset of action. However, the additional properties of propylthiouracil make it the preferred choice in this situation.
**Correct Answer:** C.