What laboratory finding is expected after administering oral fludrocortisone?

• A. Increased Serum K+
• B. Normal Serum K+
• C. Decreased Serum K+
• D. Increased Serum Na+

Answer: (C)

Administering oral fludrocortisone, a synthetic mineralocorticoid, is expected to lead to decreased serum potassium levels. Fludrocortisone acts on the kidneys to promote sodium retention and potassium excretion. This mechanism leads to an increase in sodium reabsorption in the renal tubules and consequently stimulates the secretion of potassium into the urine, resulting in decreased serum potassium levels.

As the sodium levels increase due to the enhanced reabsorption, the body can also experience an increase in blood volume and blood pressure. The retention of sodium while excreting potassium is characteristic of mineralocorticoid activity, indicating why fludrocortisone effectively reduces serum potassium levels while maintaining or increasing serum sodium levels.

In clinical practice, monitoring serum electrolytes after initiating therapy with fludrocortisone is essential, as hypokalemia (low serum potassium) can lead to various complications, particularly affecting muscle and cardiac function. This is particularly important in conditions where mineralocorticoid excess would be detrimental, emphasizing the need to balance these hormones carefully when treating related disorders.