3 Antifungals

Choosing a treatment and understanding drug classes

Antifungal selection depends on the infection site, the likely fungus, disease severity, and patient-specific risks. Topical treatment commonly addresses localized skin infections, while systemic treatment may be needed for nail or invasive disease.

The major classes differ in their targets: Azoles inhibit fungal sterol synthesis, Echinocandins inhibit fungal cell-wall synthesis, Polyenes disrupt fungal cell membranes, and Allylamines such as terbinafine inhibit squalene epoxidase.

Localized skin, oral, and nail infections

For a small area of athlete’s foot between the toes, topical clotrimazole is an option for a common localized dermatophyte infection. Apply it as directed. Avoid unsupervised antifungal–corticosteroid combination products because the corticosteroid can worsen or mask a fungal skin infection.

Nystatin oral suspension treats Candida infection in the mouth. Keep the suspension in contact with the mouth as directed and complete the prescribed course even if symptoms improve. Nystatin is minimally absorbed from the gastrointestinal tract, so it is not a treatment for systemic fungal infections.

Oral terbinafine is used for dermatophyte nail infection, or onychomycosis. Nail testing can help confirm the diagnosis when appropriate; nail changes alone do not always establish that the cause is fungal.

Systemic treatment and serious infection

Micafungin is an intravenous Echinocandin used for candidemia and certain other Candida infections. Its class interferes with fungal beta-glucan cell-wall synthesis. By contrast, Polyenes such as Amphotericin B disrupt fungal membranes.

Amphotericin B can cause kidney toxicity and electrolyte abnormalities, particularly low potassium and magnesium. Monitor renal function, electrolytes, blood counts, and other laboratory values as clinically directed. Infusion-related reactions can also occur; chills during an infusion are a reason to alert the care team.

Safety monitoring and patient teaching

Before starting oral terbinafine, assess liver function; continue liver monitoring during treatment as directed. Teach patients to promptly report possible liver-injury symptoms, including jaundice, dark urine, persistent nausea, poor appetite, or upper-right abdominal pain.

Itraconazole has a warning concerning heart failure and clinically important drug interactions. It may worsen heart failure and should not be used for onychomycosis in patients with ventricular dysfunction such as heart failure. Review the full medication list before treatment.

Monitoring should match the specific drug and route. Amphotericin B calls for attention to renal function and electrolytes, while azoles warrant careful review for drug interactions. Complete therapy as prescribed and seek clinical advice for worsening infection or serious adverse effects.

When drug-level monitoring may help

Therapeutic drug monitoring is particularly useful for selected systemic antifungals when absorption or interactions may make drug exposure unpredictable. Examples include itraconazole, posaconazole, and voriconazole. It is not routinely needed for every antifungal, such as a topical cream used for localized ringworm.