Comparative sensitivity of Naegleria fowleri to amphotericin B and amphotericin B methyl ester.

Data presented showed that Naegleria fowleri is much more sensitive to amphotericin B (AmB) than to amphotericin B methyl ester (AME). In vitro, AME was effective at concentrations of 1.0 microgram/ml whereas the parent antibiotic, AmB, was effective at concentrations of 0.0125 to 0.025 microgram/ml. In vivo, AmB, at a concentration of 2.5 mg/kg/day, produced 100% survival in mice infected with N. fowleri, but AME failed to protect infected mice even at concentrations of 30 mg/kg/day. The results support previous observations with fungi which have shown that AmB is a more potent antimicrobial agent than AME.