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.

After intravenous Candida albicans infection, rats received ornithyl amphotericin methyl ester, amphotericin B, or diluent intravenously. At doses of 0.1 and 0.5 mg/kg, the drugs were equally effective in preventing deaths. However, at doses of 2.0 mg/kg, mortality after treatment with amphotericin B was greater than that after placebo, whereas ornithyl amphotericin methyl ester was fully protective.The usefulness of amphotericin B (AMB) as an antifungal agent is limited principally by its toxicity (1). However, greater water solubility after methyl esterification of the carboxyl group of amphotericin appears to lessen nephrotoxicity without altering antifungal activity (4-6). One recently developed methylated congener is ornithyl amphotericin methyl ester (OME) (J. J. Wright, J. Albarella, L. R. Krepski, and D. Loebenberg. Abstr. Intersci. Conf. Antimicrob. Agents Chemother. 20th, New Orleans, La., abstr. no. 472, 1980). We measured survival of candida-infected rats after treatment with OME or AMB. The results of these studies are the subject of this report. OME and AMB (Fungizone intravenous; E. R. Squibb & Sons, Inc., Princeton, N.J.) were supplied by Schering Corp., Bloomfield, N.J. Candida albicans B113 was used in our studies and was kindly provided by E. Balish, University of Wisconsin, Madison. In vitro susceptibility by a broth dilution technique (3) demonstrated the MIC of both antifungal agents to be 0.31 to 0.63 p.g/ml for strain B113 and for two other isolates of C. albicans. Systemic infection of anesthetized male, outbred, cesarean-delivered adult (200 to 250 g) Sprague-Dawley rats (Hilltop Laboratories, Chatsworth, Calif.) was carried out as previously reported (7). After being thoroughly washed, overnight growths of C. albicans were diluted in sterile water so that each animal received 1.3 x 106 These results in rats with experimental candidiasis demonstrate that OME and AMB afford equal protection at doses similar to those recommended for treatment of humans. At these doses, equivalent in vivo efficacy parallels in vitro activity. However, high-dose toxicity was seen after treatment with AMB but not OME. Whether the more rapid rate of animal deaths in the AMB group is related to the effects of this agent alone or in concert with the candidal infection cannot be determined from our data as we did not study the mortality of AMB in uninfected animals. Rats received treatment by rapid intravenous infusion, and in this regard, mode of administration differed from that usually used in the treatment of humans. Thus, the greater acute toxicity of AMB found in these studies may not be directly applicable to differences expected in humans. The lack of similar toxicity after OME treatment may be related to enhanced water solubility contributed by methyl esterification. Our studies only examined the effect of treatment on survival. Had histological examinations or quantitative organ cultures also been performed, other differences between the treatments might have been detected.In summary, OME showed in vit...