**Core Concept**
Systemic fungal infections require antifungal medications that can effectively cross the blood-brain barrier and target the fungal cells. The ideal antifungal agent should have a broad spectrum of activity, minimal toxicity, and the ability to penetrate into the central nervous system.

**Why the Correct Answer is Right**
The drug of choice for treating systemic fungal infections is Amphotericin B. It is a polyene antifungal that binds to ergosterol in the fungal cell membrane, leading to cell lysis and death. Amphotericin B is particularly effective against Aspergillus and Candida species, which are common causes of systemic fungal infections. It is often administered intravenously and can be used in combination with other antifungal agents for severe infections.

**Why Each Wrong Option is Incorrect**
**Option A:** Fluconazole is a triazole antifungal that is primarily used for treating mucocutaneous and vaginal candidiasis. While it has a broad spectrum of activity, it is not the first-line treatment for systemic fungal infections.
**Option B:** Voriconazole is a triazole antifungal that is effective against Aspergillus and Candida species. However, it is generally reserved for patients who are allergic to Amphotericin B or have a history of severe reactions to this medication.
**Option C:** Caspofungin is an echinocandin antifungal that inhibits fungal cell wall synthesis. While it is effective against Candida species, it is not the first-line treatment for systemic fungal infections.

**Clinical Pearl / High-Yield Fact**
When treating systemic fungal infections, it is essential to consider the patient's underlying immune status, the severity of the infection, and any potential allergies to antifungal medications. Amphotericin B should be used cautiously in patients with renal impairment, as it can cause nephrotoxicity.

**Correct Answer:** C. Amphotericin B.