**Core Concept**
Tinea unguium is a fungal infection of the nails caused by dermatophytes, such as Trichophyton rubrum and Trichophyton mentagrophytes. Effective treatment requires antifungal agents that can penetrate the nail plate and reach the site of infection.

**Why the Correct Answer is Right**
Griseofulvin is a polyene antifungal agent that works by inhibiting microbial cell division. It is lipophilic, allowing it to penetrate the nail plate and reach the site of infection in the nail bed. Griseofulvin is particularly effective against dermatophytes, making it the preferred treatment for tinea unguium. The mechanism of action involves binding to microtubules, disrupting the fungal cell cycle and ultimately leading to fungal cell death.

**Why Each Wrong Option is Incorrect**
**Option A:** Amphotericin B is a polyene antifungal agent, but it is primarily used to treat systemic fungal infections, not superficial infections like tinea unguium. Its use is limited by its potential for nephrotoxicity.
**Option B:** Miconazole is an imidazole antifungal agent that is effective against a broad range of fungal pathogens, but it is not typically used to treat tinea unguium due to its poor penetration into the nail plate.
**Option D:** Nystatin is a polyene antifungal agent that is primarily used to treat cutaneous and mucocutaneous fungal infections, but it is not effective against dermatophytes and is not typically used to treat tinea unguium.

**Clinical Pearl / High-Yield Fact**
Griseofulvin is the only oral antifungal agent that can effectively treat tinea unguium, but it requires prolonged treatment (3-6 months) and can have significant side effects, including gastrointestinal upset and teratogenicity.

✓ Correct Answer: C. Griseofulvin.