Activities of fluconazole (UK 49,858) and ketoconazole against ketoconazole-susceptible and -resistant Candida albicans.

We have compared the activities of fluconazole and ketoconazole against ketoconazole-susceptible and -resistant strains of Candida albicans in a neutropenic-site rabbit model. Oral treatment with fluconazole resulted in much higher serum and extravascular concentrations of this antifungal agent than did comparable doses of ketoconazole. Fluconazole had no additional in vivo activity against the ketoconazole-susceptible strains; no fungicidal activity was observed with peak drug levels as high as approximately 75 micrograms/ml in the infection sites. Significant fungistatic activity against the ketoconazole-resistant strains was observed with fluconazole treatment (80 mg/kg), but not with less fluconazole (20 mg/kg) or with ketoconazole (approximately 67 mg/kg). In vitro susceptibility tests separated the ketoconazole-susceptible strains from the ketoconazole-resistant strains, but the results were variable when the resistant strains were tested with fluconazole.