DISCREPANCIES BETWEEN MIC AND MLC VALUES OF AMPHOTERICIN-B AGAINST ISOLATES OF ASPERGILLUS SPECIES

There is little information addressing the phenomena of discrepancy be tween minimal inhibitory concentrations (MIG) and minimal lethal conce ntrations (MLC) values of amphotericin B (AMB) to clinical isolates of fungi. This study assessed in vitro activity of AMB against 70 clinic al isolates of aspergilli: 30 strains of Aspergillus fumigatus, 20 str ains of Aspergillus flavus and 20 strains of Aspergillus niger. Suscep tibility tests were accomplished using a macro broth dilution procedur e, with special emphasis on ascertainment of MLCs. AMB exhibited low M IC values against all clinical isolates. While we did not identify any AMB resistant isolates among 70 Aspergillus spp. studied as judged by MIC levels, analysis of the data demonstrated a clear discrepancy bet ween the MIC and MLC levels of AMB obtained against clinical isolates of Aspergillus spp. The MLC values of AMB were significantly higher th an the MIC values with MIC 50 and MIC 90 of 0.29 and 0.5 mu g/ml, resp ectively, at the second reading time, and MLC 50 and MLC 90 of 2.31 an d 9.24 mu g/ml respectively (p < 0.001). Additionally, minimal lethal concentrations in 36/70 (51%) of aspergillal isolates studied produced drug concentrations above those which can usually be sustained in pat ient plasma or tissue.