This study was undertaken to identify prescribing policies likely to favour or limit fluconazole resistance within a clinical department. Fluconazole exposure within the infectious diseases and clinical haematology units was investigated, and data were compared with in vitro susceptibility of Candida albicans isolates obtained in these units. Fluconazole utilization was determined by the number of fluconazole treatment-days per 100 hospitalization days (penetration index). In the infectious diseases unit, separate evaluations for low-dose fluconazole (50 mg) prescribed as intermittent or prolonged treatment, and for higher-dosing schedules (fluconazole 200 mg) were made. Susceptibility of C. albicans isolates was surveyed in a broth microdilution assay by measuring the inhibitory concentration 50% (IC50). The penetration index (PI) for fluconazole 50mg declined from 1992 to 1977 in infectious diseases (P= 0.0048). In the meantime, total usage of fluconazole increased, due to increased prescribing of fluconazole 200 mg (P = 0.0724). The IC50 of C. albicans isolates tested in infectious diseases decreased between 1994 and 1996 from 7.33 mg/ml to 1.64 mg/ml (P = 0.0075). In clinical haematology, declines in C. albicans IC50 and fluconazole PI were not significant (P = 0.35 and P = 0.07, respectively). These data suggest that prolonged or repeated exposure to low-dose fluconazole, rather than total cumulative use, was associated with fluconazole resistance in the infectious diseases unit. Moreover, restoration of a normal ecology was observed when low-dose prolonged or intermittent prescriptions were reduced.
Copyright 2001 The Hospital Infection Society.