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The sordarins are a new class of antifungal drugs with a novel and unusual mode of action in antifungal therapies. These compounds interfere with protein synthesis through inhibition of protein elongation factor 2 (2, 3). The sordarins have shown in vitro activity against Candida species, Pneumocystis carinii, and some filamentous fungi (5). They have demonstrated synergy or additive effects against yeasts, Aspergillus spp., and Scedosporium apiospermum when combined with other systemic antifungal agents (M. E. Alvarez, E. Herreros, A. Sanchez-Sousa, D. Gargallo-Viola, and F. Baquero, Abstr. 38th Intersci. Conf. Antimicrob. Agents Chemother., abstr. J-12, p. 454). In vivo, these compounds have shown efficacy in murine models of candidosis, and a recent report has pointed out activities of sordarins in murine histoplasmosis (1, 4). In addition, sordarins display good bioavailability and low toxicity in murine models (1).

The azasordarins are a new family of sordarins characterized by the presence of a 6-methylmorpholin-2-yl group with different N-4 substituents instead of the sugar moiety and show an improved profile of biological properties. GW 471558 is an azasordarin that shows in vitro activity against clinical isolates of yeasts and filamentous fungi (E. Herreros, M. J. Almela, S. Lozano., and D. Gargallo-Viola, Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. J-202, p. 353; E. Herreros, M. J. Almela, S. Lozano, C. M. Martinez, and D. Gargallo-Viola, Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. J-201, p. 353; M. Lozano-Chiu, V. L. Paetznich, J. R. Rodriguez, and J. Rex, Abstr. 40th Intersci. Conf. Antimicrob. Agents Chemother., abstr. J-292, p. 351). However, the number of clinical isolates included in previous studies has been limited. This work evaluated the in vitro activity of GW 471558 against 177 isolates of Candida spp. (123 fluconazole [FLZ] susceptible and 54 with decreased susceptibility to FLZ) and compared the results obtained with those obtained with amphotericin B (AMB), itraconazole (ITZ), ketoconazole (KTZ), and flucytosine (5FC).

Organisms. A collection of 177 clinical isolates were tested. Isolates were recovered during 1998 and 1999 from 62 Spanish hospitals. Tables 1 and 2 display the species distribution. Sixty-four strains were recovered from oropharyngeal exudates, 58 were from blood cultures, 15 were from vaginal samples, and 40 were from other specimens. Each strain represented a unique isolate from a patient and was sent to our laboratory for identification or antifungal susceptibility testing. Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 were included as quality control strains in each set of experiments.

Antifungal susceptibility testing. A broth microdilution test was performed by using the National Committee for Clinical Laboratory Standards (NCCLS) reference method (6), with minor modifications (RPMI-2% glucose) (7). GW 471558 (Glaxo-Wellcome S.A., Madrid, Spain), AMB (Squibb, Madrid, Spain), FLZ (Pfizer, Madrid, Spain), ITZ (Janssen Farmaceútica, Madrid, Spain), KTZ (Janssen Farmaceútica), and 5FC (Sigma Aldrich Química, Madrid, Spain) were obtained as standard powders. Stock solutions were prepared in 100% dimethyl sulfoxide (Sigma Aldrich Química), except for 5FC, which was dissolved in sterile distilled water. Sterile flat-bottom microtitration trays were prepared with the antifungal agents and were inoculated with 100 µl into each well (final inocula, 0.5 × 10⁵ to 2.5 × 10⁵ CFU/ml). Spectrophotometric readings were performed with a Labsystems IEMS Reader MF (Labsystems, Madrid, Spain) at 540 nm. The MIC of GW 471558 was defined as the lowest concentration resulting in 95% inhibition of growth compared to that of a drug-free control (Lozano-Chiu et al., 40th ICAAC). The MIC of AMB was defined as 80% inhibition, and the MICs of 5FC, FLZ, ITZ, and KTZ were defined as 50% inhibition.

Statistical analysis. Data are reported as the MIC ranges and the MICs of each antifungal agent necessary to inhibit 50% (MIC₅₀) and 90% (MIC₉₀) of the isolates tested. The significance of the differences in the distribution of MICs of GW 471558 and the other antifungal agents between isolates was determined by the unpaired Student t test; P < 0.01 was considered to show a statistically significant difference. The correlation among the MICs of the antifungal agents was determined by Pearson's r coefficient that was expressed over a maximum value of 1. MICs were transformed on log₂ data. Control limits for quality control strains were defined as ranges which included 1 doubling concentration on either side of the mode. All statistical analyses were done with the Statistical Package for the Social Sciences, version 10.0 (SPSS S.L., Madrid, Spain).