## **Core Concept**
Hypokalemia refers to lower than normal potassium levels in the blood, which can result from various causes including certain medications, hormonal imbalances, and specific diseases. The question tests the understanding of conditions and substances that lead to hypokalemia.

## **Why the Correct Answer is Right**
The correct answer involves understanding which of the listed options cause hypokalemia.
- **a) Frusemide**: This is a loop diuretic that acts by inhibiting the sodium-potassium-chloride cotransporter in the ascending limb of the loop of Henle. This action leads to increased excretion of potassium, sodium, and chloride, resulting in hypokalemia.
- **b) Cortisol**: This glucocorticoid hormone has a mineralocorticoid effect at high levels, which can lead to potassium excretion in the urine and thus contribute to hypokalemia.
- **c) Amiloride**: This is a potassium-sparing diuretic that acts by blocking epithelial sodium channels in the collecting duct, thereby reducing sodium reabsorption and decreasing potassium secretion. It is used to prevent hypokalemia.
- **d) Addison's disease**: This condition involves adrenal insufficiency leading to decreased production of aldosterone, a mineralocorticoid that promotes sodium retention and potassium excretion. Decreased aldosterone levels result in hyperkalemia, not hypokalemia.

## **Why Each Wrong Option is Incorrect**
- **Option C: Amiloride** is incorrect because it is a potassium-sparing diuretic used to prevent hypokalemia, not cause it.
- **Option D: Addison's disease** is incorrect because it leads to hyperkalemia due to the lack of aldosterone, not hypokalemia.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while loop diuretics like **Frusemide** and certain hormonal conditions can cause hypokalemia, potassium-sparing diuretics like **Amiloride** and conditions with decreased mineralocorticoid activity like **Addison's disease** do not cause hypokalemia and can actually prevent it or lead to hyperkalemia, respectively.

## **Correct Answer: A.**