In vitro susceptibilities of yeasts to a new antifungal triazole, SCH 39304: effects of test conditions and relation to in vivo efficacy

Abstract

We used six candidal strains (two Candida albicans and one each of four other species) to study the effects of test conditions on the activity of SCH 39304 compared with that of fluconazole in broth macro-and microdilution assays. Increasing the inoculum from 102 to 105 yeasts per ml raised the MICs for all isolates up to >512-fold. In contrast, results with a 50% turbidimetric endpoint (50% inhibitory concentration; IC,,2) varied no more than twofold. Similar effects were seen with fluconazole, and both drugs were found to have an associated delay in onset of action. Acidity was found to increase both MICs and IC1,2s. Other effects were observed among four synthetic media, but a consistent pattern was not identified. (1-6, 8, 10, 12, 15, 16, 20 [7,18,23]) and one each of C. glabrata (R87), C. tropicalis (F26), C. parapsilosis (3288), and C. lusitaniae * Corresponding author.(ATCC 64125). In addition, 39 isolates of C. albicans were used. These included 32 strains from a panel selected for their variable susceptibilities to an unrelated antifungal agent, flucytosine (18, 21), and 7 strains selected from among clinical isolates from our collection. Another strain was isolated from a patient whose ketoconazole treatment failed (strain K3, also identified by others as KB [9,10,18]). A final C. albicans isolate, strain F662, used previously with strain C17 to evaluate the effect of inoculum size on results obtained with fluconazole (18), was also used for inoculum studies. Locally isolated clinical isolates of C. glabrata (six strains), C. tropicalis (three strains), and C. parapsilosis (three strains) were tested with a single set of conditions. Isolates which had been stored in yeast nitrogen broth (YNB; Difco Laboratories, Detroit, Mich.) with 10% glycerol at -70°C were thawed and maintained on Sabouraud dextrose 3% agar plates (Sab-Dex broth, BBL Microbiology Systems, Cockeysville, Md.; Bacto-Agar, Difco). For studies, subcultures were inoculated into. 20 ml of YNB and incubated at 37°C overnight.Media and buffers. A 2 x concentration of unbuffered SAAMF was prepared as previously described (11), except that cystine was replaced with equimolar amounts of cysteine (14); filter sterilized (cellulose nitrate membrane; pore size, 0.20 pum; Nalge Co., Rochester, N.Y.); and stored at 4°C. This was the medium used for all of the experiments, except when specifically noted otherwise. YNB was prepared as recommended by the manufacturer to a lOx concentration, filter sterilized, and stored at 4°C. Minimal essential medium with Hanks balanced salt solution and RPMI 1640 medium (both from Sigma) were prepared on the day of use as recommended by the manufacturer. YNB and SAAMF were diluted to lx with deionized water, and all media were buffered, adjusted to the appropriate pH, and sterilized by filtration.

Effects of temperature on anti-Candida activities of antifungal antibiotics

“…Nevertheless, relative growth of a yeast in the presence of a single inhibitor concentration is a valid comparative measure of the inherent susceptibility of yeast strains and species at inhibitor concentrations below the MIC, and it may be therefore indicate more subtle potential differences in the response of isolates to low drug concentrations than can be detected or predicted with MIC endpoints. This might explain why much more substantial effects of temperature on yeast susceptibility were found in this study than in MICbased studies that found little or no influence of temperature on susceptibility in vitro (1,3,13,16,17).…”

“…Most studies have shown minor or no differences in MICs of various antifungal agents tested against yeasts at temperatures ranging from 22 to 37°C (1,3,13,16,17). However, Block et al (2) noted a considerable increase in the susceptibility of Cryptococcus neoformans to flucytosine at 37°C compared with that at 32°C, while precisely the opposite effect of temperature was noted by Johnson et al, working with nystatin (14), and Galgiani et al, working with flucytosine (11), both in tests with Candida spp.…”

Multicenter evaluation of a broth macrodilution antifungal susceptibility test for yeasts

“…The titration curve for the effect of amphotericin B is much sharper than exists with the other drugs studied. In addition, the onset of the effect of 5-FC and azoles is delayed, allowing growth to proceed for some period before inhibition is initiated (17,23). In antibacterial susceptibility testing, an analogous problem has been encountered for sulfa drugs tested by an agar diffusion test; in that circumstance an end point criterion of 80% inhibition has been adopted (2, 3).…”

Treatment of murine coccidioidal meningitis with SCH39304

“…Itraconazole is a new antifungal triazole which has been effective in a rabbit model of cryptococcal meningitis (8); in human coccidioidal meningitis, its use has been limited to a few cases (13). Clinical studies have concentrated on the more water soluble triazole fluconazole, which appears to be effective (12), SCH39304 is a new antifungal azole with great in vitro potency (7), similar to that of itraconazole, and increased penetration of the cerebrospinal fluid (6), similar to that of fluconazole. In the present work, we evaluated SCH39304 in the treatment of murine coccidioidal meningitis and compared its efficacy with those of itraconazole and fluconazole.…”