## **Core Concept**
Trilostane is a medication used in the management of Cushing's syndrome. It works by inhibiting a key enzyme involved in the biosynthesis of steroids. Understanding its mechanism of action requires knowledge of adrenal steroidogenesis.

## **Why the Correct Answer is Right**
The correct answer involves the inhibition of **3β-hydroxysteroid dehydrogenase** (3β-HSD), an enzyme crucial for the production of steroids, including cortisol, from pregnenolone in the adrenal glands. By inhibiting this enzyme, trilostane effectively reduces the synthesis of cortisol, thereby helping to manage Cushing's syndrome.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because trilostane's mechanism does not primarily involve the inhibition of **11β-hydroxylase**, another enzyme in the steroidogenesis pathway but not the one targeted by trilostane.
- **Option B:** This option is incorrect as trilostane does not work by inhibiting **17α-hydroxylase**, an enzyme involved in earlier steps of steroidogenesis.
- **Option D:** This option is incorrect because trilostane's action is not through the inhibition of **21-hydroxylase**, an enzyme critical in the production of cortisol and aldosterone but not the target of trilostane.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that trilostane is used to treat Cushing's syndrome by specifically inhibiting **3β-hydroxysteroid dehydrogenase**. This results in decreased cortisol production. Monitoring for adrenal insufficiency is crucial during treatment.

## **Correct Answer:** . Inhibition of 3β-hydroxysteroid dehydrogenase.