In vitro susceptibilities of fungal isolates against amphotericin B and voriconazole in Aspergillus keratitis: A comparative study

Objectives: To study the susceptibility patterns of clinical isolates of Aspergillus species to amphotericin B and voriconazole. Materials and Methods: Fifty isolates of Aspergillus species (21 A. flavus , 14 A. fumigatus and 15 A. niger ) from keratitis cases were tested for their susceptibilities to amphotericin B and voriconazole by a broth microdilution method, standardized in our laboratory. The relative MIC 50 units were calculated from the absolute MIC 50 (μg/ml) upon topical prescription dose in gm/100 ml. Results: The MIC values of amphotericin B for A. fumigatus and A. niger ranged between 0.2 mg/L to 6.25 mg/L (MIC 50; 1.56 mg/L and MIC 90; 6.25 mg/L) and for A. flavus between 0.78-6.25 mg/L (MIC 50 and MIC 90; 6.25 mg/L). MICs of voriconazole for A. fumigatus were in the ranges of 0.1 to 0.2 mg/L, for A. niger 0.05 to 0.2 mg/L (MIC 50 and MIC 90; 0.2 mg/L for both fungi) and against A. flavus 0.05 to 0.39 mg/L (MIC 50 ; 0.2 mg/L and MIC 90 ; 0.39 mg/L). The relative MIC 50 of voriconazole against all the three Aspergillus species was 0.002, compared to those of amphotericin B which were 0.104 against A. fumigatus and A. niger and 0.416 against A. flavus . Conclusion: Voriconazole had lower MIC values and relative MICs than amphotericin B against Aspergillus species, the commonest fungi causing keratitis in this part of the country. Combined with its reported higher bio-availability, it appears far superior to amphotericin B for the treatment of fungal keratitis.