Itraconazole susceptibilities of fluconazole susceptible and resistant isolates of five Candida species

Epidemiology and prevalence of oropharyngeal candidiasis in Spanish patients with head and neck tumors undergoing radiotherapy treatment alone or in combination with chemotherapy

OBJECTIVE

To describe the oropharyngeal candidiasis (OPC) prevalence in Spanish patients with head and neck cancer undergoing radiotherapy, alone or combined with chemotherapy. Secondary objectives were to determine the prevalence of Candida species colonization, and to explore whether different Candida species colonizing the oral cavity and the treatment were associated with a higher prevalence of OPC.

METHODS

This is an observational, cross-sectional, multicentre study, conducted in Spanish radiation oncology units. Patients were diagnosed with head and neck cancer and started a radiotherapy treatment alone or combined with chemotherapy at the moment of their inclusion (N = 92).

RESULTS

The OPC prevalence was 26 %. The identification of colonizing pathogens was performed in 49 patients, and Candida albicans was the dominant yeast (69 %), while non-albicans Candida was only found in 15 patients (31 %). Patients with C. albicans colonization had a significant higher prevalence of OPC compared to patients colonized by non-albicans Candida (p = 0.0273), but no difference was found regarding the OPC prevalence in patients receiving only radiotherapy compared to patients with both radiotherapy and chemotherapy treatments.

CONCLUSIONS

Our data represent a step further in the knowledge of Candida species present in Spanish patients with head and neck tumors under radiation therapy. This is an essential step to manage the prophylaxis and treatment of OPC, since it might lead to severe clinical complications causing treatment interruption and, thus, representing a reduction in anti-tumor efficacy.

Candida tropicalis in human disease

Candida tropicalis is one of the more common Candida causing human disease in tropical countries; the frequency of invasive disease varies by geography causing 3--66% of candidaemia. C. tropicalis is taxonomically close to C. albicans and shares many pathogenic traits. C. tropicalis is particularly virulent in neutropenic hosts commonly with hematogenous seeding to peripheral organs. For candidaemia and invasive candidiasis amphotericin B or an echinocandin are recommended as first-line treatment, with extended-spectrum triazoles acceptable alternatives. Primary fluconazole resistance is uncommon but may be induced on exposure. Physicians in regions where C. tropicalis is common need to be mindful of this lesser-described pathogen.

High incidence of antifungal drug resistance in Candida tropicalis

Drug resistance among yeasts is an increasing problem. Isolates of Candida krusei and Candida glabrata are recognized as having reduced susceptibility to fluconazole and resistance to this drug has also arisen in Candida albicans isolated from AIDS patients on long term azole therapy. Candida tropicalis (CT) is being increasingly isolated from human disease and is associated with invasive infection, however, data regarding this organism's drug susceptibility is limited. We report our findings on 60 isolates of CT isolated from patients with serious infection in the North West of England. Over 60% of isolates were from adult Intensive Care Unit (ICU) patients, and almost half were from the respiratory tract. Susceptibility to fluconazole, flucytosine, itraconazole and ketoconazole were tested by standardised methods - 48% of the isolates were resistant to fluconazole (MIC > 12.5 mg/l), and 10% had intermediate susceptibility (MIC 6.25-12.5 mg/l). For flucytosine 17% of isolates were resistant (MIC > 8 mg/l) and 22% had intermediate susceptibility (MIC 2-8 mg/l). Three isolates were resistant to both drugs. For itraconazole 17% of isolates were resistant (MIC > 1 mg/l), and 12% showed intermediate susceptibility (MIC 0.5-1 mg/l). Resistance to ketoconazole was seen in 33% of isolates (MIC > 1 mg/l) and 10% showed intermediate susceptibility (MIC 0.5-1 mg/l). Differences in the degree of cross resistance between the azole drugs was observed. Candida tropicalis should be added to the list of yeasts in which drug resistance is commonly found. Given the high invasiveness of Candida tropicalis, its affinity for patients on ICU and the high incidence of drug resistance in this species, identification and susceptibility tests should be performed on all yeast isolates from patients on ICU.

An open multicentre comparative study of the efficacy, safety and tolerance of fluconazole and itraconazole in the treatment of cancer patients with oropharyngeal candidiasis

Oropharyngeal candidiasis is a frequent infection in cancer patients who receive cytotoxic drugs. In this study, the efficacy, safety and tolerance of fluconazole and itraconazole were compared in non-neutropenic cancer patients with oropharyngeal candidiasis. Of 279 patients who were randomised between the two treatment groups, 252 patients were considered to be eligible (126 in each group). The clinical cure rate was 74% for fluconazole and 62% for itraconazole (P=0.04, 95% Confidence Interval (CI): 0.5-23.3%). The mycological cure rate was 80% for fluconazole and 68% for itraconazole (P=0.03, 95% CI: 1.2-22.6%). The safety and tolerance profile of both drugs were comparable. This study has shown that in patients with cancer and oropharyngeal candidiasis, fluconazole has a significantly better clinical and mycological cure rate compared with itraconazole.

Antifungal therapy--state of the art at the beginning of the 21st century

The most relevant information on the present state of the art of antifungal chemotherapy is reviewed in this chapter. For dermatomycoses a variety of topical antifungals are available, and safe and efficacious systemic treatment, especially with the fungicidal drug terbinafine, is possible. The duration of treatment can be drastically reduced. Substantial progress in the armamentarium of drugs for invasive fungal infections has been made, and a new class of antifungals, echinocandins, is now in clinical use. The following drugs in oral and/or intravenous formulations are available: the broad spectrum polyene amphotericin B with its new "clothes"; the sterol biosynthesis inhibitors fluconazole, itraconazole, and voriconazole; the glucan synthase inhibitor caspofungin; and the combination partner flucytosine. New therapy schedules have been studied; combination therapy has found a significant place in the treatment of severely compromised patients, and the field of prevention and empiric therapy is fast moving. Guidelines exist nowadays for the treatment of various fungal diseases and maintenance therapy. New approaches interfering with host defenses or pathogenicity of fungal cells are being investigated, and molecular biologists are looking for new targets studying the genomics of pathogenic fungi.

Antifungal drug resistance

The increasing incidence of invasive fungal infections is the result of many factors, including an increasing number of patients with severe immunosuppression. Although new drugs have been introduced to combat this problem, the development of resistance to antifungal drugs has become increasingly apparent, especially in patients who require long-term treatment or who are receiving antifungal prophylaxis, and there is growing awareness of shifts of flora to more-resistant species. The frequency, interpretation, and, in particular, mechanism of resistance to current classes of antifungal agents, particularly the azoles (where resistance has climbed most prominently) are discussed in this review.

Epidemiology of clinical isolates of Candida albicans and their susceptibility to triazoles

The study comprised strains of Candida albicans isolated from patients hospitalised in a tertiary care hospital during a 2-year period. In total 851 strains were cultured, including 379 (44.5%) strains from internal medicine patients, 243 (28.6%) from surgical patients and 229 (26.9%) from patients in the surgical intensive care unit. The strains were tested for susceptibility to the triazoles: fluconazole and itraconazole. There were 523 (61.5%) strains susceptible, 11 strains (1.3%) showed intermediate susceptibility and 317 (37.2%) were resistant to fluconazole, while 403 (47.3%) strains were susceptible, 43 (5.1%) intermediately susceptible and 405 (47.6%) resistant to itraconazole. Regular surveillance of fungal resistance patterns should be carried out and there should be prudent use of hospital triazole usage.

Decrease in Candida albicans strains with reduced susceptibility to fluconazole following changes in prescribing policies

This study was undertaken to identify prescribing policies likely to favour or limit fluconazole resistance within a clinical department. Fluconazole exposure within the infectious diseases and clinical haematology units was investigated, and data were compared with in vitro susceptibility of Candida albicans isolates obtained in these units. Fluconazole utilization was determined by the number of fluconazole treatment-days per 100 hospitalization days (penetration index). In the infectious diseases unit, separate evaluations for low-dose fluconazole (50 mg) prescribed as intermittent or prolonged treatment, and for higher-dosing schedules (fluconazole 200 mg) were made. Susceptibility of C. albicans isolates was surveyed in a broth microdilution assay by measuring the inhibitory concentration 50% (IC50). The penetration index (PI) for fluconazole 50mg declined from 1992 to 1977 in infectious diseases (P= 0.0048). In the meantime, total usage of fluconazole increased, due to increased prescribing of fluconazole 200 mg (P = 0.0724). The IC50 of C. albicans isolates tested in infectious diseases decreased between 1994 and 1996 from 7.33 mg/ml to 1.64 mg/ml (P = 0.0075). In clinical haematology, declines in C. albicans IC50 and fluconazole PI were not significant (P = 0.35 and P = 0.07, respectively). These data suggest that prolonged or repeated exposure to low-dose fluconazole, rather than total cumulative use, was associated with fluconazole resistance in the infectious diseases unit. Moreover, restoration of a normal ecology was observed when low-dose prolonged or intermittent prescriptions were reduced.

Resistance of Candida species to antifungal agents used in the treatment of onychomycosis: a review of current problems

Treatment of Candida infections with fluconazole has resulted in the emergence of drug resistance, a problem particularly apparent in HIV-infected patients. Frequently, the yeast is also cross-resistant to itraconazole and other azoles. In neutropenic patients fluconazole therapy or prophylaxis has caused overgrowth and infection by inherently less susceptible species of Candida, principally C. glabrata and C. krusei. Consequently, the use of intermittent long-term azole therapy to treat onychomycosis could result in changes in the commensal yeast flora of patients--either resistance or pathogen shift. An 'off-study' investigation undertaken in patients receiving either continuous terbinafine or intermittent itraconazole for toenail onychomycosis (L.I.ON. study) showed no evidence of changes in the yeast species present, nor in their sensitivity to itraconazole or fluconazole. Although intermittent itraconazole seems unlikely to cause problems in this respect, the situation with regard to intermittent fluconazole therapy of onychomycosis needs further study.

The use of fluconazole and itraconazole in the treatment of Candida albicans infections: a review

Candida albicans is responsible for most fungal infections in humans. Fluconazole is well established as a first-line management option for the treatment and prophylaxis of localized and systemic C. albicans infections. Fluconazole exhibits predictable pharmacokinetics and is effective, well tolerated and suitable for use in most patients with C. albicans infections, including children, the elderly and those with impaired immunity. Prophylactic administration of fluconazole can help to prevent fungal infections in patients receiving cytotoxic cancer therapy. The increasing use of fluconazole for the long-term prophylaxis and treatment of recurrent oral candidosis in AIDS patients has led to the emergence of C. albicans infections that are not responsive to conventional doses. Second-line therapy with a wider spectrum antifungal, such as itraconazole, should be sought if treatment with fluconazole fails. A solution formulation of itraconazole has recently been introduced to overcome the poor and variable absorption of its original capsule formulation. Efficacy and tolerability studies in HIV-positive or immunocompromised patients with C. albicans infections have shown that, although itraconazole solution is as effective as fluconazole, it is less well tolerated as first-line therapy. Itraconazole solution can be effective in AIDS patients with C. albicans infections that are non-responsive to fluconazole. No efficacy or tolerability data are available on the use of itraconazole solution in children or the elderly.

The management of superficial candidiasis

Superficial Candida infection includes several common conditions, most often related to some underlying local or systemic predisposition. Appropriate identification of the pathogen is important in the management of candidiasis as the result of differences in susceptibility among species and strains of Candida to different antifungal drugs. Treatment options are reviewed for oropharyngeal candidiasis, vaginal candidiasis, cutaneous candidiasis, paronychia and onychomycosis, and chronic mucocutaneous candidiasis. Because of the importance of predisposing conditions for candidiasis, adjunctive measures to abate these may be useful, although they are seldom effective in immunocompromised patients.

Comparison of the API Candida system with the AUXACOLOR system for identification of common yeast pathogens

Two commercial systems for the identification of yeasts were evaluated by using 159 clinical isolates that had also been identified by conventional biochemical and morphological methods. The API Candida system correctly identified 146 isolates (91.8%), and the AUXACOLOR system correctly identified 145 isolates (91.2%). However, of the 146 isolates identified by the API Candida system, 23 required supplemental biochemical tests or morphological assessment to obtain the correct identification. The AUXACOLOR system gave no identification in 13 cases (8.2%), while the API Candida system gave an unreadable profile in only one case. Incorrect identifications were more common with the API Candida system (12 isolates; 7.5%) than with the AUXACOLOR system (1 isolate; 0.6%).

Fungal infection in the intensive care unit

Fungal infection in critically ill patients is an increasingly prevalent problem. Candida spp. cause the majority of these infections in ICU. They occur most commonly in patients with severe underlying illness, multiple courses of antibiotics and intravascular catheters. Clinical diagnosis is difficult due to nonspecific signs and the frequent occurrence of widespread superficial colonization with Candida spp. in ventilated patients. Most patients are diagnosed using inferential evidence of infection, such as persistent pyrexia despite antibiotics, raised serum C-reactive protein and the presence of individual risk factors. Amphotericin B and fluconazole are the most commonly used anti-fungals dependent on the identity of the fungus. Most of these infections are endogenous; however, a proportion may be caused via the hands of healthcare staff or contaminated medical equipment.

Activity of SCH 56592 compared with those of fluconazole and itraconazole against Candida spp

The in vitro activity of Schering 56592, a new azole drug, was compared with those of fluconazole and itraconazole against 103 isolates of Candida comprising 10 different species. Schering 56592 was more active than itraconazole and fluconazole, and it was active against many fluconazole-resistant isolates.

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.

Cloning of Candida albicans genes conferring resistance to azole antifungal agents: characterization of CDR2, a new multidrug ABC transporter gene

Resistance to azole antifungal agents in Candida albicans can be mediated by multidrug efflux transporters. In a previous study, we identified at least two such transporters, Cdr1p and Benp, which belong to the class of ATP-binding cassette (ABC) transporters and of major facilitators, respectively. To isolate additional factors potentially responsible for resistance to azole antifungal agents in C. albicans, the hypersusceptibility of a Saccharomyces cerevisiae multidrug transporter mutant, delta pdr5, to these agents was complemented with a C. albicans genomic library. Several new genes were isolated, one of which was a new ABC transporter gene called CDR2 (Candida drug resistance). The protein Cdr2p encoded by this gene exhibited 84% identity with Cdr1p and could confer resistance to azole antifungal agents, to other antifungals (terbinafine, amorolfine) and to a variety of metabolic inhibitors. The disruption of CDR2 in the C. albicans strain CAF4-2 did not render cells more susceptible to these substances. When the disruption of CDR2 was performed in the background of a mutant in which CDR1 was deleted, the resulting double delta cdr1 delta cdr2 mutant was more susceptible to these agents than the single delta cdr1 mutant. The absence of hypersusceptibility of the single delta cdr2 mutant could be explained by the absence of CDR2 mRNA in azole-susceptible C. albicans strains. CDR2 was overexpressed, however, in clinical C. albicans isolates resistant to azole antifungal agents as described previously for CDR1, but to levels exceeding or equal to those reached by CDR1. Interestingly, CDR2 expression was restored in delta cdr1 mutants reverting spontaneously to wild-type levels of susceptibility to azole antifungal agents. These data demonstrate that CDR2 plays an important role in mediating the resistance of C. albicans to azole antifungal agents.

Multiple efflux mechanisms are involved in Candida albicans fluconazole resistance

Fluconazole-susceptible Candida albicans strains accumulated [3H]fluconazole at a rate of approximately 2 pmol/min per 10(9) cells. Fluconazole accumulation was not affected by the pretreatment of cells with sodium azide or with 2-deoxyglucose. The rate of fluconazole accumulation became saturated at high fluconazole concentrations and was not affected by the addition of ketoconazole, and there was no fluconazole accumulation in cells incubated at 4 degrees C. A fluconazole-resistant mutant of C. albicans SGY-243 was isolated following growth enrichment in fluconazole-containing medium. Cells of the mutant strain, designated FR2, showed a reduced rate of fluconazole accumulation compared with SGY-243 and were not resistant to other azole antifungal agents. The rates of fluconazole accumulation by C. albicans FR2 and the other azole-resistant strains, B59630, AD, and KB, were increased in the presence of sodium azide, suggesting that fluconazole resistance in these strains may be associated with an energy-dependent drug efflux. Fluconazole-resistant C. albicans strains all contained elevated amounts (2- to 17-fold) of mRNA encoding Cdr1, and an ATP-binding cassette-type transporter. In addition, C. albicans FR2 also contained increased amounts of mRNA encoding Benr, a major facilitator superfamily transporter. These results suggest that fluconazole enters C. albicans cells by facilitated diffusion and that fluconazole resistance may involve energy-dependent drug efflux associated with increased expression of Benr and/or Cdr1.