**Question:** Which one of the following drugs causes increased concentration of Na' & CI- in urine with normal bicarbonate?

**Core Concept:**
The question is asking about a drug that affects urinary electrolyte excretion, specifically sodium (Na+) and chloride (Cl-) ions, without significantly altering urine pH (bicarbonate level). This is important as it relates to understanding how diuretics work, their effects on the nephron, and the kidney's role in maintaining electrolyte balance.

**Why the Correct Answer is Right:**
The correct answer is **D:** Furosemide (Lasix). Furosemide is a loop diuretic, a type of diuretic that works in the loop of Henle in the nephron. Loop diuretics increase the renal tubular secretion of Na+ and Cl-, which results in increased excretion of these ions in the urine. Since furosemide primarily affects the distal convoluted tubule and collecting duct, it does not significantly alter urine pH (bicarbonate level), making it the correct answer.

**Why Each Wrong Option is Incorrect:**

A. **Thiazide diuretics (e.g., hydrochlorothiazide):** While thiazide diuretics also increase Na+ and Cl- excretion in urine, they can lower urine pH due to their ability to inhibit the sodium-chloride co-transporter (NCC) in the distal convoluted tubule, resulting in increased bicarbonate excretion.

B. **Spironolactone:** Spironolactone is an aldosterone antagonist, blocking the effects of aldosterone on the collecting duct, which leads to increased K+ excretion and decreased Na+ reabsorption. It does not affect urine pH significantly.

C. **Amiloride:** Amiloride is a mineralocorticoid receptor antagonist that inhibits the epithelial sodium channel (ENaC) in the distal convoluted tubule, leading to increased sodium excretion and decreased urine osmolality. However, unlike thiazide diuretics, amiloride does not significantly alter urine pH.

D. **Furosemide (Lasix):** As explained above, Furosemide increases Na+ and Cl- excretion without significantly affecting urine pH, making it the correct answer among the given options.

**Clinical Pearl:** Diuretics play a crucial role in managing edema, hypertension, and electrolyte imbalances. Understanding the pharmacology of different classes of diuretics is essential for effective clinical decision-making and treatment planning.