Oral Amphotericin B is NOT Effective for Treating Mold Infections
Oral amphotericin B should not be used for systemic mold infections—it has negligible oral bioavailability and is only indicated for non-invasive gastrointestinal candidiasis. The FDA label explicitly states that amphotericin B for injection is intended for "progressive, potentially life-threatening fungal infections" including aspergillosis, mucormycosis, and other mold infections, but only via intravenous administration 1.
Why Oral Amphotericin B Fails for Mold Infections
Pharmacokinetic Barriers
Amphotericin B is amphipathic with extremely poor water and lipid solubility, resulting in negligible absorption when administered orally 2, 3. The drug simply does not achieve systemic levels sufficient to treat invasive fungal infections when given by mouth. While experimental nanoparticle formulations have achieved 1.5-10.5% bioavailability in rat models 4, these remain investigational and are not clinically available.
Current Clinical Applications of Oral Amphotericin B
The only legitimate use of oral amphotericin B is for localized gastrointestinal candidiasis where systemic absorption is not required:
- Candida cystitis: Amphotericin B deoxycholate bladder irrigation at 50 mg/L for fluconazole-resistant species 5
- Oral/esophageal candidiasis: Amphotericin B deoxycholate oral suspension 100 mg/mL 4 times daily for refractory disease 5
- Pediatric Candida endocarditis: 5-fluorocytosine given "by mouth" with amphotericin B (though the amphotericin component is intravenous) 6
These applications rely on direct mucosal contact, not systemic absorption.
Treatment of Mold Infections Requires Intravenous Therapy
For Invasive Aspergillosis
- First-line: Mold-active triazole (voriconazole or isavuconazole) intravenously 7
- Alternative: Liposomal amphotericin B 3-5 mg/kg IV daily 7
- Oral therapy is reserved for step-down after clinical improvement with IV agents
For Mucormycosis
- First-line: Liposomal amphotericin B 5-10 mg/kg IV daily 8
- Alternative: Amphotericin B lipid complex 5 mg/kg IV daily (non-CNS disease) 8
- Salvage: Isavuconazole or posaconazole (oral formulations available for step-down only) 8
For Other Mold Infections (Blastomycosis, Histoplasmosis)
- Severe disease: Lipid amphotericin B 3-5 mg/kg IV or amphotericin B deoxycholate 0.7-1 mg/kg IV for 1-2 weeks 9, 10
- Step-down: Itraconazole 200 mg orally after initial IV response 9, 10
Critical Clinical Pitfalls
Never attempt oral amphotericin B for systemic mold infections—this represents treatment failure before you start. The drug will not be absorbed.
Distinguish between investigational and approved formulations: Novel oral encochleated amphotericin B (MAT2203) is under investigation for cryptococcal meningitis 11 but remains experimental and is not approved for any indication, let alone mold infections.
Recognize when oral therapy is appropriate: Only after achieving clinical stability with IV antifungals can you transition to oral mold-active azoles (voriconazole, isavuconazole, posaconazole, itraconazole)—never oral amphotericin B.
Avoid confusion with topical/local use: Bladder irrigation and oral suspension for mucosal candidiasis are fundamentally different from treating invasive mold disease, which requires therapeutic serum and tissue levels.
The evidence is unequivocal: mold infections require intravenous amphotericin B formulations or mold-active azoles. Oral amphotericin B has no role in this setting due to absent systemic bioavailability 2, 3.