Influence of Fungicidal Activity against Candida tropicalis on the Efficacy of Micafungin and Liposomal Amphotericin B in a Neutropenic Murine Lethal Infection Model

Abstract

Objectives: To investigate the correlation between in vitro killing activity and in vivo efficacy of micafungin (MCFG) and liposomal amphotericin B (L-AMB) against Candida tropicalis in a neutropenic murine lethal infection model. Methods:Candida albicans (one strain) and C. tropicalis (three strains) were tested in time-kill studies. Cyclophosphamide-treated mice were inoculated intravenously with each strain. One day after inoculation, antifungals were administered intravenously once daily for 1 or 3 days. Results: MCFG exhibited fungicidal activity against C. albicans ATCC 90029 and C. tropicalis SP-20142, and fungistatic activity against C. tropicalis ATCC 42678 and SP-20047. The ED₅₀s (dosage that results in 50% survival) of MCFG for C. tropicalis ATCC 42678 and SP-20047 (4.1–50 mg/kg) were higher than those for other strains (1.6–12 mg/kg). A 1-day course of MCFG was not effective against C. tropicalis ATCC 42678 and SP-20047 at the clinical dose (5 mg/kg), which achieved an AUC level almost equal to that of 100 mg in humans, whereas a 3-day course of 5 mg/kg MCFG was efficacious against all strains. In contrast, L-AMB showed fungicidal activity against all strains tested and the ED₅₀s of L-AMB were 0.08–0.65 mg/kg. In both treatment regimens, the minimum effective doses of L-AMB (≤0.5 mg/kg) were less than the clinical dosage (≤5 mg/kg). Conclusions: The in vivo efficacy of MCFG and L-AMB showed a correlation with the in vitro killing activity. At the clinical dose, L-AMB exerted anti-C. tropicalis activity within a shorter treatment period than MCFG.