Concentration-dependent synergy and antagonism within a triple antifungal drug combination against Aspergillus species: analysis by a new response surface model.

Triple antifungal combinations are used against refractory invasive aspergillosis without an adequate understanding of their pharmacodynamic interactions. We initially studied the in vitro triple combination of voriconazole, amphotericin B, and caspofungin against Aspergillus fumigatus, A. flavus, and A. terreus by a spectrophotometric microdilution broth method after 48 h of incubation. We then analyzed these results with a recently described nonlinear mixture response surface E(max)-based model modified to assess pharmacodynamic interactions at various growth levels. The new model allows flexibility in all four parameters of the E(max) model and is able to describe complex pharmacodynamic interactions. Concentration-dependent pharmacodynamic interactions were found within the triple antifungal combination. At the 50% growth level, synergy (median interaction indices of 0.43 to 0.82) was observed at low concentrations of voriconazole (<0.03 mg/liter) and amphotericin B (

Antifungal interactions within the triple combination of amphotericin B, caspofungin and voriconazole against Aspergillus species.

OBJECTIVES: The in vitro effects of caspofungin combined with voriconazole and amphotericin B were tested in triplicate experiments against nine clinical isolates of Aspergillus fumigatus, Aspergillus flavus and Aspergillus terreus. METHODS: The isolates were tested against a range of concentrations of voriconazole (0.015-1.0 mg/L), caspofungin (0.125-256 mg/L) and five concentrations of amphotericin B (0.1-0.5 mg/L) with a microdilution chequerboard method based on the CLSI M38-A reference method and the results were analysed with the fractional inhibitory concentration (FIC) index. The effect of individual drugs on the FIC index of each of the double combinations was also evaluated. RESULTS: The triple combination of voriconazole, caspofungin and amphotericin B against all Aspergillus spp. was synergistic (FIC index 0.49-0.57) at low median concentrations of amphotericin B (0.10-0.22 mg/L) and voriconazole (0.07-0.15 mg/L) over a wide range of caspofungin concentrations (4.32-17.28 mg/L). Antagonistic interactions (FIC index 1.65-2.15) were found at higher median concentrations of amphotericin B (0.3-0.5 mg/L) and voriconazole (0.23-0.68 mg/L) over a similarly wide range of caspofungin concentrations (1.47-32 mg/L). CONCLUSIONS: These concentration-dependent interactions may have important clinical implications, which require further evaluation in animal models of invasive aspergillosis.

Laboratory diagnosis of invasive mycoses.

Rising numbers of immunocompromised patients have led to an ever-increasing population at risk of invasive fungal disease. Much has been achieved in the laboratory diagnosis of these infections, such as advances in blood culture systems, and the development of new biochemical, antigen detection assays, and molecular methodologies. More standardized susceptibility testing guidelines provide for better therapeutic interventions. In an era of economic cutbacks in health care, future challenges include the development of cost-effective and technically simplified systems, which provide early detection and identification of common and emerging fungal pathogens. It will, however, take some time to establish the clinical relevance of these new methodologies in different patient populations.