Antifungal activity of a new triazole, D0870, compared with four other antifungal agents tested against clinical isolates of Candida and Torulopsis glabrata

Recent developments in pradimicin-benanomicin and triazole antibiotics

Fungal infections are on the rise as the number of patients with compromised immune systems continues to increase. The need for safer and more effective antifungals has resulted in the search for novel drug classes and for modifications to existing classes, with the aim of enhancing their antifungal spectra and potency. In this review, two classes of antifungals are discussed: the pradimicin-benanomicin antibiotics and the newer triazole derivatives. These have activity against Candida spp., Cryptococcus neoformans and Aspergillus spp., as well as variable activity against other less commonly encountered fungi including Pneumocystis carinii. Pradimicins-benanomicins are generally fungicidal, whereas the newer azoles appear to be selectively fungicidal to Cryptococcus neoformans and Aspergillus spp. Pradimicin-benanomicin acts by binding to mannan and alters membrane integrity. One water-soluble pradimicin candidate, BMS-181184, has been selected for clinical development. The triazoles act by inhibiting cytochrome P450 sterol 14a-demethylase. Four triazoles either currently in clinical development (voriconazole and D0870) or being considered as clinical candidates (ER-30346 and Sch 56592) will be discussed. The antifungal spectra, pharmacokinetic and toxicologic data in animals, and efficacy results in experimental infection models will be reviewed for BMS-181184 and the four newer triazoles. Results from the early clinical trials for voriconazole and D0870 will also be discussed.

Practice guidelines for the treatment of candidiasis. Infectious Diseases Society of America

Infections due to Candida species are the most common of the fungal infections. Candida species produce a broad range of infections, ranging from nonlife-threatening mucocutaneous illnesses to invasive process that may involve virtually any organ. Such a broad range of infections requires an equally broad range of diagnostic and therapeutic strategies. This document summarizes current knowledge about treatment of multiple forms of candidiasis and is the guideline of the Infectious Diseases Society of America (IDSA) for the treatment of candidiasis. Throughout this document, treatment recommendations are scored according to the standard scoring scheme used in other IDSA guidelines to illustrate the strength of the underlying data. The document covers 4 major topical areas. The role of the microbiology laboratory. To a greater extent than for other fungi, treatment of candidiasis can now be guided by in vitro susceptibility testing. The guidelines review the available information supporting current testing procedures and interpretive breakpoints and place these data into clinical context. Susceptibility testing is most helpful in dealing with infection due to non-albicans species of Candida. In this setting, especially if the patient has been treated previously with an azole antifungal agent, the possibility of microbiological resistance must be considered. Treatment of invasive candidiasis. In addition to acute hematogenous candidiasis, the guidelines review strategies for treatment of 15 other forms of invasive candidiasis. Extensive data from randomized trials are really available only for therapy of acute hematogenous candidiasis in the nonneutropenic adult. Choice of therapy for other forms of candidiasis is based on case series and anecdotal reports. In general, both amphotericin B and the azoles have a role to play in treatment. Choice of therapy is guided by weighing the greater activity of amphotericin B for some non-albicans species (e.g., Candida krusei) against the lesser toxicity and ease of administration of the azole antifungal agents. Flucytosine has activity against many isolates of Candida but is not often used. Treatment of mucocutaneous candidiasis. Therapy for mucosal infections is dominated by the azole antifungal agents. These drugs may be used topically or systemically and have been proven safe and efficacious. A significant problem with mucosal disease is the propensity for a small proportion of patients to suffer repeated relapses. In some situations, the explanation for such a relapse is obvious (e.g., relapsing oropharyngeal candidiasis in an individual with advanced and uncontrolled HIV infection), but in other patients the cause is cryptic (e.g., relapsing vaginitis in a healthy woman). Rational strategies for these situations are discussed in the guidelines and must consider the possibility of induction of resistance over time. Prevention of invasive candidiasis. Prophylactic strategies are useful if the risk of a target disease is sharply elevated in a readily identified group of patients. Selected patient groups undergoing therapy that produces prolonged neutropenia (e.g., some bone-marrow transplant recipients) or who receive a solid-organ transplant (e.g., some liver transplant recipients) have a sufficient risk of invasive candidiasis to warrant prophylaxis.

[Fluconazole-resistant Candida species from HIV infected patients with recurrent Candida stomatitis: cross resistance to itraconazole and ketoconazole]

In vitro susceptibility to fluconazole of Candida species isolated from 83 HIV-infected patients treated with fluconazole because of recurrent Candida stomatitis was monitored over a period of two years. A microdilution assay with high-resolution antifungal assay (HR) medium and RPMI 1640-medium were compared. In vitro less susceptible and fluconazole resistant C. species were observed in 23 patient at the end of the study. The Candida isolates recovered from oral rinsing fluids at the beginning and the end of study were tested for crossresistance to itraconazole and ketoconazole. Susceptibility to ketoconazole and to itraconazole was reduced using RPMI 1640-medium. Susceptibility of the isolates to fluconazole was not influenced by the assay medium. In 21 patients in vitro fluconazole resistant or less susceptible C. albicans were observed. 9 of 21 isolates showed crossresistance to itroconazole and ketoconazole, in 10 isolates only crossresistance to itraconazole was observed. During fluconazole treatment double infections due to combination of C. albicans and C. glabrata or C. krusei increased from 20% to 78% C. krusei was resistant to the three azoles. C. glabrata was less susceptible (4-8 mg/l) or resistant (> 8 mg/l) to fluconazole and resistant to itraconazole and ketoconazole High dosed intravenous fluconazole treatment with 400 to 600 mg daily failed in 11 patients with fluconazole resistant C. albicans and in 3 (3/10) patients with les susceptible C. albicans isolates.

Efficacy of D0870 treatment of experimental Candida vaginitis

In this study, oral administration of the triazole D0870 was compared to oral administration of fluconazole in the treatment of experimental vaginal candidiasis. With an estrogen-dependent murine model of Candida albicans vaginal infection, the effects of D0870 on several isolates, including fluconazole-susceptible and -resistant isolates, were tested. D0870, at doses of 0.5 and 2.5 mg/kg of body weight given once over the course of a 10-day infection, was effective in eradicating vaginitis caused by fluconazole-susceptible laboratory and clinical isolates, respectively. In contrast, a stricter treatment regimen (every 24 to 48 h) with 10 and 25 mg of fluconazole per kg was required to achieve similar reductions in vaginal fungal titers induced by the same isolates. Whereas fluconazole was consistently ineffective in infections induced by fluconazole-resistant isolates, as predicted by in vitro susceptibility tests, D0870 was effective, although a daily regimen of 25 mg/kg was required. Additional studies showed that despite the in vitro activity of D0870 against two clinical Candida glabrata isolates, neither D0870 nor fluconazole was effective at daily doses as high as 100 and 125 mg/kg, respectively. Taken together, although D0870 failed to show efficacy against experimental C. glabrata vaginitis, D0870 was superior to fluconazole in the treatment of experimental C. albicans vaginitis caused by isolates that were either susceptible or resistant to fluconazole.

Azole resistance in Candida

Resistance of Candida to azoles is an increasing problem. Susceptibility testing of Candida against fluconazole and ketoconazole is now feasible and desirable. Good correlation of resistance in vitro with clinical failure of fluconazole therapy has now been shown in mucosal candidiasis. The relationship, if any, between resistance and clinical failure in the context of invasive candidiasis is not clear at present and additional correlative work needs to be done. Monitoring of resistance trends in Candida is clearly important now.

Variations in DNA subtype and antifungal susceptibility among clinical isolates of Candida tropicalis

Candida tropicalis has been known to be a major cause of invasive Candida infection. Numerous reports have documented C. tropicalis as the most common species of Candida other than C. albicans. The epidemiology and antifungal susceptibility of C. tropicalis are poorly defined. A series of 89 clinical isolates of C. tropicalis from 56 patients hospitalized at seven different U.S. medical centers were analyzed by restriction endonuclease analysis of genomic DNA (REAG) using the restriction enzymes Sfil and BssHII followed by pulsed-field gel electrophoresis (PFGE). The MICs of the isolates for amphotericin B, 5-fluorocytosine (5FC), fluconazole, itraconazole, and D0870 were determined by microbroth dilution testing. A total of 49 different DNA types were identified among the 89 isolates. Generally, each DNA type represented an individual patient, and serial isolates from the same patient were the same DNA type. Small clusters of patients infected with the same DNA type of C. tropicalis suggested possible nosocomial transmission. The MICs of the various antifungal agents were amphotericin B 0.5 to 2.0 micrograms/ml (MIC90 = 2.0 micrograms/ml), 5FC 0.25 to 1.0 microgram/ml (MIC90 = 0.5 microgram/ml), fluconazole 0.25 to 8.0 micrograms/ml (MIC90 = 1.0 microgram/ml), itraconazole 0.03 to 1.0 microgram/ml (MIC90 = 0.5 microgram/ml), and D0870 0.007 to 0.12 microgram/ml (MIC90 = 0.03 microgram/ml). These data support previous observations that infections caused by C. tropicalis frequently originate from the patient's own endogenous flora. Clusters of a single strain in individual hospitals also suggests that limited nosocomial transmission may occur.

In vitro studies of activities of the antifungal triazoles SCH56592 and itraconazole against Candida albicans, Cryptococcus neoformans, and other pathogenic yeasts

We investigated the effects of various assay conditions on the activities of two antifungal drugs, SCH56592 and itraconazole, against seven species of fungi by the broth macrodilution testing procedure proposed by the National Committee for Clinical Laboratory Standards (NCCLS). For both drugs, which are insoluble in water, the concentration and type of solubilizing agent produced differences in drug activity. Starting inoculum size differences from 10(2) to 10(5) yeast cells per ml resulted in approximately a fourfold effect on the MIC of both drugs, but other significant differences were not observed with variations in synthetic medium composition, pH, buffering reagent, or incubation temperature. Under standardized conditions of reference method M27-T with 1% polyethylene glycol as the solubilizing agent, median MICs of SCH56592 and itraconazole of 60 and 125 mg/ml, respectively, were demonstrated for 110 strains (12 to 23 strains for each of seven species). Broth microdilution results were typically severalfold higher than broth macrodilution results. We conclude that the NCCLS standard reference method can be applied without modification to the testing of SCH56592 and itraconazole, but particular attention to solubilizing the agents is critical to obtaining consistent results.

Clinical evaluation of a dried commercially-prepared microdilution panel for antifungal susceptibility testing

A commercially-prepared dried broth microdilution panel (Sensititre) was compared with a reference microdilution method for antifungal susceptibility testing of two reference yeast strains and 98 clinical isolates of Candida spp. The antifungal agents tested include 5-fluorocytosine (5FC), fluconazole, itraconazole, and D0870. Microdilution testing was performed according to National Committee for Clinical Laboratory Standards (NCCLS) recommendations. Minimum inhibitory concentration (MIC) endpoints were read visually after 48 hours of incubation and were assessed independently for each microdilution panel. The MICs for the reference strains were within published control limits for both reference and Sensititre microdilution panels. Discrepancies among MIC endpoints of no more than two dilutions (two wells) were used to calculate the percent agreement. An acceptable level of agreement between Sensititre and reference panels was observed for all antifungal agents when tested against the 98 clinical isolates. Agreement ranged from 83% for itraconazole to 93% for 5FC. The Sensititre dried microdilution panel appears to be a viable alternative to inhouse prepared microdilution panels and to the NCCLS microdilution reference method.

Fluconazole. An update of its antimicrobial activity, pharmacokinetic properties, and therapeutic use in vaginal candidiasis

Fluconazole is a bis-triazole antifungal drug which has a pharmacokinetic profile characterised by its high water solubility, low affinity for plasma proteins, and metabolic stability. After a single 150 mg oral dose, therapeutic concentrations in vaginal secretions are rapidly achieved and are sustained for a duration sufficient to produce high clinical and mycological responses in nonimmunocompromised patients with vaginal candidiasis (candidosis). At this dosage, clinical and mycological responses have compared favourably with responses achieved after multiple dose regimens of other oral and intravaginal antifungal agents. Clinical efficacy rates have ranged between 92 and 99% at short term evaluation (5 days post-treatment). At 80 to 100 days post-treatment clinical efficacy rates of 91% have been reported. In addition, limited data indicate that fluconazole is more effective than placebo as prophylactic treatment of frequently recurring vaginal candidiasis. Single oral doses of fluconazole 150 mg are well tolerated. Most frequently observed adverse events are gastrointestinal symptoms, which are generally mild and transient in nature. Thus, fluconazole is a valuable alternative to established systemic and intravaginal azole antifungal drugs which are used to treat vaginal candidiasis. Moreover, in view of its favourable patient acceptability and compliance profile compared with alternative treatments, single-dose oral fluconazole should be considered as a first-line therapeutic choice for the treatment of women with vaginal candidiasis.

Comparison of visual and spectrophotometric methods of MIC endpoint determinations by using broth microdilution methods to test five antifungal agents, including the new triazole D0870

A study to compare three different methods for reading MIC endpoints tested by the broth microdilution modification of the National Committee for Clinical Laboratory Standards (Villanova, Pa.) reference method was conducted. MICs of amphotericin B, flucytosine, fluconazole, itraconazole, and a new triazole, D0870, were determined for five reference yeast strains and 100 clinical isolates of Candida spp. MICs were read visually according to National Committee for Clinical Laboratory Standards guidelines from microdilution trays that had been (VS) and had not been (V) shaken. MICs were also determined spectrophotometrically (SP) at 492 nm. SP endpoints were determined as the concentrations resulting in a > or = 50% inhibition of growth (flucytosine and azoles) and a > or = 90% inhibition of growth (amphotericin B) relative to control growth. The five reference strains were tested nine times each against all five antifungal agents, and the MIC results for each reading method were compared with a 3-log2 dilution reference range determined by the macrodilution (M27-P) method. Overall, 84 to 100% of the MICs determined by V, 93 to 100% of those determined by VS, and 89 to 100% of those determined by SP fell within the 3-log2 dilution reference range for each reference strain and antifungal agent. Reproducibility was 99% for V and SP and 98% for VS. Agreement among the three methods of reading ranged from 97 to 99%. Excellent agreement among reading methods was also observed for all antifungal agents when tested against 100 clinical isolates. Agreement between the standard V method (no agitation) and VS ranged from 99 to 100%, and that between V and SP ranged from 89 to 99%. The VS and SP reading methods provided more definitive endpoints than the V method, which does not involve shaking.