Which statement best describes NSAID-induced edema mechanism?

• A. Inhibits COX, increases prostaglandin synthesis, causing afferent arteriolar dilation.
• B. Inhibits COX, increases prostaglandin synthesis, leading to edema.
• C. Inhibits COX, reduces prostaglandin synthesis, decreases afferent arteriolar dilation, reduces renal blood flow, and increases proximal Na reabsorption, causing edema.
• D. Inhibits COX and increases aldosterone production, leading to edema.

Answer: (C)

NSAIDs cause edema mainly by reducing prostaglandin synthesis in the kidney. By inhibiting COX, they lower levels of kidney prostaglandins (like PGE2 and PGI2), which normally help keep the afferent arteriole dilated and limit proximal sodium reabsorption. With fewer prostaglandins, the afferent arteriole constricts, decreasing renal blood flow and GFR, while proximal Na reabsorption increases, promoting sodium and water retention. The combination of reduced renal perfusion and increased sodium reabsorption leads to edema.

This matches the described mechanism: decreased prostaglandin synthesis leading to less afferent dilation, reduced renal blood flow, and more proximal sodium reabsorption causing edema. The other options imply increased prostaglandin synthesis or involve aldosterone, which isn’t how NSAIDs cause edema.