Activities of voriconazole, itraconazole and amphotericin B in vitro against 590 moulds from 323 patients in the voriconazole Phase III clinical studies

Introduction: Fungal pathogens from the voriconazole trials were identified and tested for susceptibility at two reference laboratories. Methods: MICs were measured using CLSI M38-A 48 h microdilution methodology. Results: Moulds from 29 genera and 38 species were isolated from 18 countries. Aspergillus spp. predominated (69%), followed by Scedosporium spp. (11.5%). Aspergillus fumigatus (292/590, 49.5%) was the most common species, followed by Scediosporium apiospermum (9.7%) and Aspergillus terreus (7.3%). The bronchi, lungs and sinuses yielded 45% of the isolates (57% of aspergilli), with 24% from the oropharynx/oesophagus. Other sites included blood/catheter (7.3%) and CNS (5.2%). MIC₉₀s of itraconazole and voriconazole for Aspergillus spp. were the same (0.5 mg/L), but 17 Aspergillus isolates were itraconazole-resistant (MICs ≥1-16 mg/L). Additionally, in 31 A. fumigatus and 23 A. terreus isolates, amphotericin MICs were ≥2.0 mg/L. Voriconazole MICs exceeded 4 mg/L in only 5.8% (34/590) of the isolates, including one A. fumigatus (8.0 mg/L), 9/11 Scedosporium prolificans, 10/13 Fusarium solani and all 9 Zygomycetes. Most were also not susceptible to itraconazole or amphotericin B. A notable increase in MIC (more than two doubling dilutions) during voriconazole therapy was seen for one A. fumigatus isolate. The response rate of voriconazole-treated patients with isolate MICs ≥4.0 mg/L was 38% when compared with 52% for those with MICs <4.0 mg/L. Conclusions: Voriconazole shows activity, in vitro, similar to that of itraconazole against a wide range of moulds. It is also active against some isolates not susceptible to itraconazole or amphotericin B, but not the Zygomycetes. The relationship between voriconazole MIC and clinical outcome requires further study.