Resistance to amphotericin B does not emerge during treatment for invasive aspergillosis

Emergence of resistance to antifungal drugs during therapy for invasive aspergillosis has received scant attention. We recovered Aspergillus isolates from six patients with invasive aspergillosis, who were receiving amphotericin B before fungal isolation. Although isolates were susceptible to amphotericin B in vitro, none of the patients survived. The MIC of amphotericin B for isolates was similar to that for isolates from 35 patients with no prior exposure to amphotericin B. Laboratory attempts to produce amphotericin B resistance in Aspergillus were unsuccessful. These data indicate that emergence of resistance to amphotericin B is uncommon during therapy for invasive aspergillosis.