Which of the following antifungal agents is primarily used for invasive fungal infections?

Amphotericin B is primarily used for invasive fungal infections due to its broad-spectrum antifungal activity and its efficacy against serious, systemic mycoses. It targets the fungal cell membrane by binding to ergosterol, causing increased membrane permeability and ultimately leading to cell death. This makes it particularly effective for treating severe infections caused by organisms such as Candida species and Aspergillus species, which are often seen in immunocompromised patients or those with severe systemic fungal infections.

While fluconazole, terbinafine, and itraconazole are also antifungal agents, they are used primarily for less severe infections or for prophylactic purposes in certain at-risk patients. Fluconazole, for example, is mainly effective against a narrower range of fungi and is often used for less serious infections. Terbinafine is primarily used for dermatophyte infections and onychomycosis and is not typically the first choice for invasive systemic mycoses. Itraconazole is used to treat fungal infections as well, but it is generally more suitable for less severe or localized infections.

In summary, the effectiveness of amphotericin B in penetrating deep tissues and its ability to combat severe fungal infections positions it as the agent of choice for invasive fungal infections.