**Core Concept**
Amphotericin B is a polyene antifungal medication that can cause nephrotoxicity due to its ability to bind to ergosterol in the fungal cell membrane, leading to cell lysis. To minimize its adverse effects, particularly nephrotoxicity, patients are often premedicated with certain medications.

**Why the Correct Answer is Right**
The correct answer is **C. Mannitol**. Mannitol is an osmotic diuretic that can exacerbate nephrotoxicity caused by amphotericin B. Administering mannitol with amphotericin B can further decrease renal blood flow and glomerular filtration rate, increasing the risk of acute kidney injury.

**Why Each Wrong Option is Incorrect**
**Option A:** Furosemide is a loop diuretic that can help manage fluid overload and edema associated with amphotericin B therapy. It does not exacerbate nephrotoxicity.

**Option B:** H2 blockers, such as ranitidine, can help manage gastrointestinal side effects of amphotericin B, such as nausea and vomiting. They do not interact with the medication's nephrotoxic effects.

**Clinical Pearl / High-Yield Fact**
When administering amphotericin B, it is essential to monitor renal function closely, especially in patients with pre-existing kidney disease or those receiving concomitant nephrotoxic medications. This may involve regular measurement of serum creatinine levels and urine output.

**Correct Answer:** C. Mannitol.