In vitro susceptibility studies of Cryptococcus neoformans isolated from patients with no clinical response to amphotericin B therapy

The in vitro activities of three antifungal drugs alone and in combination were evaluated against five isolates of Cryptococcus neoformans using time-kill curves (TKC). The isolates were from AIDS patients who had either died or had failed to show a clinical response during amphotericin B (AMB) treatment. AMB, fluconazole (FCZ) and flucytosine (5FC), and combinations of the drugs (AMB plus 5FC, AMB plus rifampicin (RIF) and FCZ plus 5FC), were evaluated. With all five isolates AMB did not show fungicidal activity; instead, a persistent or tolerant effect was observed. Combinations of AMB plus 5FC and AMB plus RIF showed a clear synergic effect, except for one isolate tested with AMB plus RIF. In contrast, the FCZ plus 5FC combination did not inhibit growth of any isolate.