**Question:** Which of the following is least nephrotoxic?

A. Gentamicin
B. Ceftriaxone
C. Metformin
D. Ibuprofen

**Core Concept:** Nephrotoxicity is the harmful effect on the nephrons (functioning units of the kidney) due to exposure to certain substances or medications. The less nephrotoxic a substance is, the less likely it is to cause kidney damage when taken appropriately.

**Why the Correct Answer is Right:**

* D. Ibuprofen: Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that primarily targets the cyclooxygenase (COX) enzymes. Although it can cause renal dysfunction in high doses or with prolonged use, it is generally considered less nephrotoxic compared to other NSAIDs like indomethacin or naproxen.

**Why Each Wrong Option is Incorrect:**

* A. Gentamicin: Gentamicin is an aminoglycoside antibiotic that can cause nephrotoxicity due to its accumulation in the renal tubules, leading to toxicity.
* B. Ceftriaxone: Ceftriaxone is a beta-lactam antibiotic that can cause nephrotoxicity in some patients, typically due to hypovolemia, hypotension, or renal impairment.
* C. Metformin: Metformin is an oral hypoglycemic agent used for type 2 diabetes mellitus. Although it can cause lactic acidosis in rare cases, it is generally considered less nephrotoxic than other antidiabetic drugs like sulfonylureas or insulin.

**Clinical Pearl:** When evaluating patients with renal dysfunction, consider the potential nephrotoxicity of medications and adjust the dosage or choose less nephrotoxic alternatives when appropriate.

**Correct Answer:** C. Metformin