What is the appropriate prescription for treating a deep invasive fungal infection in an adult?

Treatment of Deep Invasive Fungal Infections in Adults

For invasive candidiasis, start with an echinocandin (caspofungin, micafungin, anidulafungin, or rezafungin) as first-line therapy; for invasive aspergillosis, initiate voriconazole as the primary agent. 1, 2

Invasive Candidiasis Treatment Algorithm

First-Line Therapy Selection

Echinocandins are the preferred initial therapy for most adults with invasive candidiasis, particularly those who are critically ill, hemodynamically unstable, or have recent azole exposure 1:

• Caspofungin: 70 mg loading dose, then 50 mg daily 1
• Micafungin: 100 mg daily 1
• Anidulafungin: 200 mg loading dose, then 100 mg daily 1
• Rezafungin: 400 mg loading dose, then 200 mg weekly (newer once-weekly option) 3

Fluconazole is an acceptable alternative (800 mg loading dose, then 400 mg daily) only for patients who are not critically ill, have no recent azole exposure, and are unlikely to harbor fluconazole-resistant species 1.

Species-Specific Considerations

The choice of antifungal must account for Candida species and susceptibility patterns:

• C. albicans: Transition from echinocandin to fluconazole is appropriate once the patient is clinically stable and susceptibility is confirmed 4, 1
• C. glabrata: Echinocandins are strongly preferred; do not transition to azoles without documented susceptibility 4, 1
• C. parapsilosis: Fluconazole is preferred if susceptible, though continuing echinocandin therapy is reasonable if the patient is improving 4
• C. krusei: Inherently fluconazole-resistant; use echinocandin or voriconazole 4

Susceptibility testing is mandatory for all bloodstream and clinically relevant Candida isolates 1.

Alternative Agents

When echinocandins and azoles cannot be used:

• Amphotericin B deoxycholate: 0.5–1.0 mg/kg daily 4
• Lipid formulation amphotericin B: 3–5 mg/kg daily 4, 1

These are reserved for situations of intolerance, limited availability, or resistance to first-line agents 4.

Duration and Monitoring

• Continue therapy for 2 weeks after documented clearance of Candida from bloodstream and resolution of attributable symptoms 1
• Remove central venous catheters whenever feasible 1
• Perform ophthalmologic examination to rule out endophthalmitis 1
• Obtain imaging (CT or ultrasound) of abdomen if candidemia persists to identify deep-seated foci 1

Chronic Disseminated Candidiasis

For hepatosplenic or other chronic disseminated candidiasis:

• Initial therapy: Lipid formulation amphotericin B (3–5 mg/kg daily) OR echinocandin for several weeks 1
• Step-down therapy: Fluconazole 400 mg daily for susceptible isolates 1
• Duration: Continue until lesions resolve on repeat imaging, typically several months 1

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Invasive Aspergillosis Treatment Algorithm

Primary Therapy

Voriconazole is the drug of choice for invasive pulmonary aspergillosis 2:

• Loading dose: 6 mg/kg IV every 12 hours for 2 doses 2
• Maintenance: 4 mg/kg IV every 12 hours, or 200 mg orally every 12 hours after stabilization 2

Alternative Primary Agents

When voriconazole cannot be used:

• Liposomal amphotericin B: 3–5 mg/kg daily 2
• Isavuconazole: Favorable safety profile with no QT prolongation and safe in renal impairment 5

Combination Therapy

A conditional recommendation exists for either combination therapy (mold-active triazole plus echinocandin) or monotherapy with a mold-active triazole alone for proven or probable invasive pulmonary aspergillosis 6. The 2025 American Thoracic Society guideline notes this is based on low-quality evidence and does not mandate combination therapy routinely 6.

However, combination therapy with caspofungin plus voriconazole or liposomal amphotericin B should be considered in critically ill patients 2.

Salvage Therapy

For refractory disease or intolerance to primary therapy:

• Caspofungin (if not used initially) 2
• Liposomal amphotericin B (if not used initially) 2
• Posaconazole: 200 mg every 8 hours orally 2

Site-Specific Considerations

• CNS aspergillosis: Voriconazole preferred due to excellent CNS penetration; carries highest mortality among all aspergillosis patterns 2
• Osteomyelitis/septic arthritis: Surgical debridement of devitalized tissue is essential alongside antifungal therapy 2
• Endocarditis: Requires surgical resection of infected valves 2

Duration

Treatment should continue until resolution or stabilization of all clinical and radiographic manifestations, which typically requires months of therapy 2. Reversal of immunosuppression is critical for favorable outcomes 2.

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Critical Pitfalls and Caveats

Empiric Therapy in ICU Patients

Empiric antifungal therapy should be considered in critically ill patients with risk factors for invasive candidiasis, no other fever source, and signs of septic shock 1. However, routine prophylactic or empiric antifungal agents targeting Candida are conditionally recommended against in non-neutropenic, non-transplant ICU patients 6.

Drug Interactions and Monitoring

• Voriconazole: Significant CYP450 interactions; requires therapeutic drug monitoring 2
• Rezafungin: Minimal drug interactions with CYP450 enzymes or major transporters 3
• Azoles: Monitor for QT prolongation (except isavuconazole) and hepatotoxicity 5

Resistance Patterns

• C. auris: Emerging multidrug-resistant pathogen; echinocandins often remain effective 7
• Azole-resistant Aspergillus: Increasing globally; susceptibility testing recommended when available 7

Special Populations

Neonates with disseminated candidiasis:

• Amphotericin B deoxycholate 1 mg/kg daily is first-line 1
• Fluconazole 12 mg/kg daily is acceptable if no prior azole prophylaxis 1
• Echinocandins should be reserved for salvage therapy in neonates 1

Rezafungin Exclusions

Rezafungin is not approved for CNS candidiasis, endocarditis, chronic disseminated candidiasis, osteomyelitis, or invasive aspergillosis 3. It is indicated only for candidemia and invasive candidiasis 3.