If a thiazide diuretic is administered for hypeension, the response seen within 24 hrs on excretion of different electrolytes is
Thiazide diuretics primarily act on the distal convoluted tubule by inhibiting the Na-Cl cotransporter. This reduces sodium and chloride reabsorption, leading to increased excretion of these ions. But what about other electrolytes? Potassium excretion may increase because of the increased sodium delivery to the distal tubule, which enhances potassium secretion. However, thiazides can also cause hypokalemia over time due to this.
Calcium excretion is decreased because thiazides increase calcium reabsorption in the distal tubule. So calcium excretion would decrease. Magnesium excretion might increase a bit because thiazides can cause magnesium loss, but it's not as pronounced as potassium.
Now, looking at the options, the correct one should show increased sodium and chloride excretion, increased potassium, decreased calcium, and maybe some magnesium. The options are not listed, but the correct answer should reflect these points. The user probably expects a detailed explanation of why thiazides have these effects on electrolytes.
**Core Concept**
Thiazide diuretics inhibit the Na-Cl cotransporter in the distal convoluted tubule, reducing sodium and chloride reabsorption. This leads to increased excretion of these ions but paradoxically decreases calcium excretion due to enhanced proximal tubule reabsorption.
**Why the Correct Answer is Right**
Thiazides cause natriuresis (Na⁺ excretion) and diuresis within hours. Chloride excretion increases due to Na⁺-Cl⁻ cotransport inhibition. Potassium excretion rises initially due to increased sodium delivery to the collecting duct, enhancing K⁺ secretion. However, calcium excretion decreases because thiazides upregulate calcium reabsorption in the distal tubule via a parathyroid hormone–independent mechanism. Magnesium excretion may also increase slightly but is less pronounced than potassium.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect if it claims increased calcium excretion—thiazides reduce calcium excretion by enhancing tubular reabsorption.
**Option B:** Incorrect if it states decreased potassium excretion—thiazides initially increase K⁺ excretion, risking hypokalemia.
**Option C:** Incorrect if it suggests no change in sodium excretion—thiazides acutely increase Na⁺ excretion by inhibiting the Na-Cl cotransporter.
**Clinical Pearl / High-Yield Fact**
Thiazides cause a "hypokalemic paradox" despite reducing total body sodium. Remember: **"Thiazides spare calcium but waste potassium."** This is a classic NEET PG/USMLE trap—confusing their effects on calcium vs. potassium excretion.
**Correct Answer: C. Increased Na⁺ and Cl⁻ excretion, decreased Ca²⁺ excretion, increased K⁺ excretion**