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Voriconazole against fluconazole-susceptible and resistant candida isolates: in-vitro efficacy compared with that of itraconazole and ketoconazole.

Nguyen MH, Yu CY.

Department of Medicine, University of Florida College of Medicine, Gainesville 32610, USA. nguyemt medicine.ufl.edu

We compared the in-vitro activity of fluconazole, itraconazole, ketoconazole and voriconazole against 67 blood isolates of Candida spp. exhibiting a wide range of fluconazole MICs (0.125 to >64 mg/L). Voriconazole was the most potent in vitro, followed by itraconazole, ketoconazole and fluconazole. Itraconazole and voriconazole had in-vitro activity against fluconazole-susceptible and -resistant candida isolates. Higher itraconazole and voriconazole MICs were observed in isolates exhibiting higher fluconazole MICs, suggesting cross-resistance. Itraconazole and voriconazole MICs of > or =16 mg/L were observed only in Candida albicans and Candida tropicalis. Candida krusei and Candida glabrata exhibited itraconazole MICs of 0.5-1 mg/L and voriconazole MICs of 0.25-0.5 mg/L.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9738846&dopt=Abstract fluconazole Diflucan



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Rapid, transient fluconazole resistance in Candida albicans is associated with increased mRNA levels of CDR.

Marr KA, Lyons CN, Rustad TR, Bowden RA, White TC.

Department of Medicine, University of Washington, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA. kmarr u.washington.edu

Fluconazole-resistant Candida albicans, a cause of recurrent oropharyngeal candidiasis in patients with human immunodeficiency virus infection, has recently emerged as a cause of candidiasis in patients receiving cancer chemotherapy and marrow transplantation (MT). In this study, we performed detailed molecular analyses of a series of C. albicans isolates from an MT patient who developed disseminated candidiasis caused by an azole-resistant strain 2 weeks after initiation of fluconazole prophylaxis (K. A. Marr, T. C. White, J. A. H. vanBurik, and R. A. Bowden, Clin. Infect. Dis. 25:908-910, 1997). DNA sequence analysis of the gene (ERG11) for the azole target enzyme, lanosterol demethylase, revealed no difference between sensitive and resistant isolates. A sterol biosynthesis assay revealed no difference in sterol intermediates between the sensitive and resistant isolates. Northern blotting, performed to quantify mRNA levels of genes encoding enzymes in the ergosterol biosynthesis pathway (ERG7, ERG9, and ERG11) and genes encoding efflux pumps (MDR1, ABC1, YCF, and CDR), revealed that azole resistance in this series is associated with increased mRNA levels for members of the ATP binding cassette (ABC) transporter superfamily, CDR genes. Serial growth of resistant isolates in azole-free media resulted in an increased susceptibility to azole drugs and corresponding decreased mRNA levels for the CDR genes. These results suggest that C. albicans can become transiently resistant to azole drugs rapidly after exposure to fluconazole, in association with increased expression of ABC transporter efflux pumps.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9756759&dopt=Abstract fluconazole Diflucan



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Mechanism of fluconazole resistance in Candida krusei.

Orozco AS, Higginbotham LM, Hitchcock CA, Parkinson T, Falconer D, Ibrahim AS, Ghannoum MA, Filler SG.

St. John's Cardiovascular Research Center, Division of Infectious Diseases, Harbor-UCLA Research and Education Institute, Torrance, California 90502, USA.

The mechanisms of fluconazole resistance in three clinical isolates of Candida krusei were investigated. Analysis of sterols of organisms grown in the absence and presence of fluconazole demonstrated that the predominant sterol of C. krusei is ergosterol and that fluconazole inhibits 14alpha-demethylase in this organism. The 14alpha-demethylase activity in cell extracts of C. krusei was 16- to 46-fold more resistant to inhibition by fluconazole than was 14alpha-demethylase activity in cell extracts of two fluconazole-susceptible strains of Candida albicans. Comparing the carbon monoxide difference spectra of microsomes from C. krusei with those of microsomes from C. albicans indicated that the total cytochrome P-450 content of C. krusei is similar to that of C. albicans. The Soret absorption maximum in these spectra was located at 448 nm for C. krusei and at 450 nm for C. albicans. Finally, the fluconazole accumulation of two of the C. krusei isolates was similar to if not greater than that of C. albicans. Thus, there are significant qualitative differences between the 14alpha-demethylase of C. albicans and C. krusei. In addition, fluconazole resistance in these strains of C. krusei appears to be mediated predominantly by a reduced susceptibility of 14alpha-demethylase to inhibition by this drug.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9756770&dopt=Abstract fluconazole Diflucan



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Analysis of fluconazole effect on Candida albicans viability during extended incubations.

Sohnle PG, Hahn BL, Fassel TA, Kushnaryov VM.

Division of Infectious Diseases, Department of Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, USa. psohnle post.its.mcw.edu

Fluconazole is an azole agent with primarily fungistatic activity in standard in vitro susceptibility tests. However, recent work has demonstrated that this drug can reduce Candida albicans viability during prolonged incubations under non-growing conditions. The present study was undertaken to examine more closely some of the parameters of this killing activity. Fungicidal effects of 1.0 microg ml-1 of fluconazole were found during 7-14-day exposures in each of two media that prevented proliferation, distilled water and metal-depleted RPMI 1640 tissue-culture medium. Fluconazole appeared to be stable after being incubated at 37 degreesC for either 7 or 14 days. Strains of C. albicans resistant to fluconazole in standard short-term growth-inhibition assays were also found to be resistant to fluconazole's effect on viability in prolonged culture, suggesting similar mechanisms of action for these effects. C. albicans yeast cells pre-incubated for 7 days in distilled water were not more sensitive to the drug in short-term susceptibility assays. Although all proliferation of the organisms in distilled water cultures appeared to cease after 3 days, fluconazole added at 7 days still reduced C. albicans viability. Therefore, the drug appeared to kill the non-proliferating organisms directly rather than preventing growth and thereby the emergence of younger organisms that would live longer. Transmission electron microscopy demonstrated damage to the cell wall-cell membrane complex and interior contents of yeast cells incubated in distilled water alone; fluconazole appeared to increase the percentages of cells so affected. In summary, extended-incubation susceptibility tests demonstrated that fluconazole has direct fungicidal activity of non-proliferating C. albicans yeast cells. These results may be relevant to the manner in which this drug promotes clearance of chronic fungal infections.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9776809&dopt=Abstract fluconazole Diflucan



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Distinct patterns of gene expression associated with development of fluconazole resistance in serial candida albicans isolates from human immunodeficiency virus-infected patients with oropharyngeal candidiasis.

Lopez-Ribot JL, McAtee RK, Lee LN, Kirkpatrick WR, White TC, Sanglard D, Patterson TF.

Department of Medicine, Division of Infectious Diseases, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284-7881, USA. ribot uthscsa.edu

Resistance to fluconazole is becoming an increasing problem in the management of oropharyngeal candidiasis in human immunodeficiency virus-infected patients. Strains obtained from five patients developed decreased fluconazole susceptibility over time. DNA strain typing confirmed the high degree of relatedness among isolates from one patient and the variability among isolates from different patients. Expression of genes involved in development of fluconazole resistance was monitored in each isolate using probes specific for ERG11 (lanosterol 14alpha-demethylase), MDR1 (a major facilitator), and CDR (ATP-binding cassette or ABC transporter) genes. Increased expression of CDR genes was detected in the series of isolates from two patients. Isolates from one of the two patients also demonstrated increased ERG11 expression, whereas isolates from the other patient did not. Increased levels of MDR1 mRNA correlated with increased resistance in sequential isolates from another patient. Initial overexpression of MDR1 with subsequent overexpression of CDR genes and a final isolate again overexpressing MDR1 were detected in serial isolates from another patient. In another patient, overexpression of these genes was not detected despite an eightfold increase in fluconazole MIC. In this patient, sequence data of the ERG11 gene revealed no point mutations associated with decreased susceptibility. Five different patterns of gene expression were observed in isolates recovered from five patients who developed resistance. Therefore, these experiments demonstrate that a variety of mechanisms or combinations of mechanisms are associated with the development of fluconazole drug resistance. Additional studies are needed to estimate the frequency and clinical impact of these mechanisms of resistance.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9797228&dopt=Abstract fluconazole Diflucan



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Fluconazole versus Candida albicans: a complex relationship.

Graybill JR, Montalbo E, Kirkpatrick WR, Luther MF, Revankar SG, Patterson TF.

Division of Infectious Diseases, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284, USA. GRAYBILL UTHSCSA.EDU

A murine model of systemic candidiasis was used to assess the virulence of serial Candida albicans strains for which fluconazole MICs were increasing. Serial isolates from five patients with 17 episodes of oropharyngeal candidiasis were evaluated. The MICs for these isolates exhibited at least an eightfold progressive increase from susceptible (MIC < 8 microg/ml; range, 0.25 to 4 microg/ml) to resistant (MIC >/= 16 microg/ml; range, 16 to >/=128 microg/ml). Virulence of the serial isolates from three of five patients showed a more than fivefold progressive decrease in the dose accounting for 50% mortality and was associated with development of fluconazole resistance. Low doses of fluconazole prolonged survival of mice infected with susceptible yeasts but failed to prolong survival following challenge with a resistant strain. In addition, a decreased burden of renal infection was noted in mice challenged with two of the three resistant strains. This was consistent with reduced virulence. Fluconazole did not further decrease the level of infection. In the isolates with a decrease in virulence, two exhibited overexpression of CDR, which encodes an ABC drug efflux pump. In contrast, serial isolates from the remaining two patients with the development of resistance did not demonstrate a change in virulence and fluconazole remained effective in prolonging survival, although significantly higher doses of fluconazole were required for efficacy. Resistant isolates from both of these patients exhibited overexpression of MDR. This study demonstrates that decreased virulence of serial C. albicans isolates is associated with increasing fluconazole MICs in some cases but not in others and shows that these low-virulence strains may not consistently cause infection.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9797229&dopt=Abstract fluconazole Diflucan



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An evaluation of the safety and efficacy of fluconazole in the treatment of onychomycosis.

Smith SW, Sealy DP, Schneider E, Lackland D.

Montgomery Center for Family Medicine, Self Memorial Hospital, Greenwood, SC 29646, USA.

Sixteen subjects were enrolled in this open-label noncomparative study to evaluate the safety and efficacy of fluconazole as a single daily dose for a period of 6 months. Liver function enzymes were monitored to assess safety. An adverse function questionnaire was used on a monthly basis to assess patient tolerance. A visual analogue scale was used to assess efficacy of treatment. After 6 months of fluconazole, all subjects experienced improvement in the appearance of their nails. None of the subjects evidenced any elevation in liver function enzymes. Adverse reactions were limited and consistent with other studies involving fluconazole. Fluconazole proved to be safe and efficacious in the treatment of onychomycosis. Further studies are needed to determine a cost-effective dosing regimen for the treatment of onychomycosis with fluconazole.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7502113&dopt=Abstract fluconazole Diflucan



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Synergy of fluconazole with human monocytes or monocyte-derived macrophages for killing of Candida species.

Garcha UK, Brummer E, Stevens DA.

Department of Medicine, Santa Clara Valley Medical Center, San Jose, CA 95128-2699, USA.

Possible synergy between fluconazole and monocyte-derived macrophages (MDM) for significant killing of Candida species and between fluconazole and monocytes for increased candidacidal activity were studied. Human serum in test medium (RPMI 1640 with 10% fresh autologous human serum) was highly fungistatic for Candida species. Fluconazole in test medium, even at high concentrations, was not fungicidal. Monocytes alone were fungicidal for all Candida species and synergized with fluconazole for increased killing of a fluconazole-sensitive and a fluconazole-resistant Candida albicans isolate. MDM obtained by culturing for 3 or 5 days were not significantly fungicidal for C. albicans but could synergize with fungistatic fluconazole for significant killing. MDM alone killed Candida krusei and Candida glabrata but did not synergize with fluconazole for significantly increased killing. These results, which demonstrate synergy of fluconazole and mononuclear phagocytes for killing, help explain the in vivo efficacy of fluconazole against candidiasis.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7594731&dopt=Abstract fluconazole Diflucan