Caspofungin in combination with amphotericin B against Candida parapsilosis

Abstract

Candida parapsilosis has emerged as an important nosocomial pathogen. In the present study, a checkerboard broth microdilution method was performed to investigate the in vitro activities of caspofungin (CAS) in combination with amphotericin B (AMB) against three clinical isolates of C. parapsilosis. Although there was a significant reduction of the MIC of one or both drugs used in combination, an indifferent interaction (fractional inhibitory concentration index greater than 0.50 and less than or equal to 4.0) was observed in 100% of cases. This finding was confirmed by killing curve studies. By a disk diffusion assay, the halo diameters produced by antifungal agents in combination were often significantly greater than those produced by each drug alone. Antagonism was never observed. In a murine model of systemic candidiasis, CAS at either 0.25 or 1 mg/kg/day combined with AMB at 1 mg/kg/day was significantly more effective than each single drug at reducing the colony counts in kidneys. Higher doses of the echinocandin (i.e., 5 and 10 mg/kg/day) combined with the polyene did not show any advantage over CAS alone. Overall, our study showed a positive interaction of CAS and AMB against C. parapsilosis.

FIG. 1.

Time-kill studies conducted with C. parapsilosis strain no. 3. AMB 1X, 0.5 μg/ml; AMB 8X, 4 μg/ml; CAS 1X, 4 μg/ml; CAS 8X, 32 μg/ml; COMBO 1X, 0.5 μg/ml AMB plus 4 μg/ml CAS; COMBO 8X, 4 μg/ml AMB plus 32 μg/ml CAS. The dotted lines represent a >99.9% growth reduction compared with the initial inoculum size (fungicidal effect). The limit of detection was 20 CFU/ml. Each datum point represents the mean ± standard deviation of results from three independent experiments.

FIG. 2.

Kidney tissue burden of neutropenic CD1 mice. The mice were infected intravenously with 3.5 × 10⁸ CFU/mice of C. parapsilosis strain no. 3. Animals were treated daily for four consecutive days with AMB at 1 mg/kg/day (AMB 1), with CAS at 0.25, 1, 5, or 10 mg/kg/day (CAS 0.25, CAS 1, CAS 5, CAS10), or with their respective combinations (COMBO 0.25, COMBO 1, COMBO 5, and COMBO10). Tissue burden experiments were performed on day 5 postinfection. The bars represent the medians. C, control; *, P < 0.016.