Strategies for managing systemic fungal infection and the place of itraconazole *
Transcription
Strategies for managing systemic fungal infection and the place of itraconazole *
Journal of Antimicrobial Chemotherapy (2005) 56, Suppl. S1, i49–i54 doi:10.1093/jac/dki224 Strategies for managing systemic fungal infection and the place of itraconazole Michael Potter1* 1 Department of Haematology, Royal Marsden Hospital (London & Sutton), Downs Road, Sutton, Surrey SM2 5PT, UK Systemic fungal infections are an increasing cause of mortality and morbidity in patients with haematological malignancies and certain other conditions associated with profound immunosuppression. The majority of such infections are caused by Aspergillus and Candida species. In recent years, the number of available drugs effective in the therapy of these difficult infections has expanded. Large clinical trials have been performed in different settings such as prophylaxis, empirical and first-line therapy. For prophylaxis, the azoles fluconazole and itraconazole have been most widely studied. These azoles are available in both oral and intravenous formulations. Itraconazole has a wide spectrum of activity including Aspergillus, Candida albicans and non-albicans species. Two large studies comparing the use of itraconazole with fluconazole for primary prophylaxis in high-risk patients who were recipients of allogeneic stem cell transplants have recently been reported. These have confirmed that itraconazole is effective in this setting in reducing the rate of systemic fungal infections. However, there are concerns with regard to increased toxicity and the potential for drug interactions with itraconazole compared with fluconazole. In the empirical setting, large randomized studies support the use of caspofungin and liposomal amphotericin B. Voriconazole and lipid-associated amphotericin B have been shown to be effective in first-line therapy and caspofungin for salvage. New approaches to management include efforts at improving diagnosis, combination antifungal therapy and treatment strategies for emerging moulds. Keywords: azoles, prophylaxis, empirical, Aspergillus, Candida Introduction Systemic fungal infections (SFIs) are the leading cause of infection-related mortality in profoundly immunosuppressed patients treated for haematological malignancies. Within this area, two groups of patients are particularly at high risk of systemic fungal infections, of the order of 10–20%. These are recipients of allogeneic stem cell transplants and patients receiving intensive chemotherapy for de novo and relapsed acute leukaemias.1,2 In these patients, systemic fungal infections are predominantly caused by Aspergillus species. Invasive aspergillosis is also common amongst certain groups of patients receiving solid organ— especially lung—transplants.1,2 Patients with chronic granulomatous disease also have a high cumulative risk of invasive aspergillosis.1,2 Non-Aspergillus mould infections remain relatively rare. These include infections by Mucor, Fusarium and Scedosporium species. There is evidence from some large institutions in the USA and other countries that the incidence of these so-called ‘emerging’ SFIs is increasing, though the absolute rate remains low compared with aspergillosis.3 Systemic candidiasis occurs with less frequency and has a lower attributable mortality in haematology patients than mould infections.4 The relative importance of these infections is higher in other fields of medicine, such as intensive care, neonatology and patients undergoing major surgery. Two major problems with regard to invasive aspergillosis are the high associated mortality and the difficulty in diagnosing these infections. In immunosuppressed patients with invasive aspergillosis, mortality rates vary from 30% to over 90%.5 The highest mortality rates are seen in recipients of allogeneic stem cell transplants and in those patients where the Aspergillus infection is disseminated, affecting the central nervous system or with diffuse lung involvement.5 In terms of diagnosis, the majority of infections diagnosed clinically are not confirmed by tissue biopsy due to the practical difficulties and risks involved in obtaining deep tissue biopsies. Most infections are therefore categorized as probable or possible as defined by EORTC/MSG diagnostic criteria.6 Preemptive treatment strategies based on the early detection of a serum marker of infection with a method allowing both high sensitivity and specificity are not yet in routine clinical practice. The reasons ............................................................................................................................................................................................................................................................................................................................................................................................................................. *Tel: +44-20-8661-3670; Fax: +44-20-8642-9634; E-mail: Mike.potter@rmh.nhs.uk ............................................................................................................................................................................................................................................................................................................................................................................................................................. i49 Ó The Author 2005. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oupjournals.org Potter for this relate to technical difficulties with assays and interpretation of the results and the lack of validated quality control systems.7 Therefore empirical treatment remains the standard clinical approach to the management of SFIs in neutropenic patients. In such patients, 80–90% of infections are pulmonary in origin.8 High-resolution pulmonary CT scanning has proved to be a highly effective clinical means of early detection of established Aspergillus infections.9,10 Certain radiographic features (for example, the halo sign and air crescent sign) have been shown to be highly specific in this regard.10 In terms of the treatment of established invasive Aspergillus infections there are a number of antifungal agents clinically available. These include amphotericin B and lipid associated products; the triazoles, itraconazole and voriconazole, and the echinocandin, caspofungin. Newer azoles (e.g. posaconazole) and echinocandins (e.g. micafungin and anidulafungin) are also being evaluated in clinical trials but are not yet licensed. The development of these newer antifungal agents has created much debate as to the optimal approach to the prophylaxis and treatment of SFIs in patients at risk of infection. recipients of chemotherapy. Significant benefits for systemic prophylaxis included reductions in the empirical use of parenteral antifungal therapy and more importantly reductions in the incidence of superficial and invasive fungal infection and attributable fungus-related mortality. Although systemic prophylaxis did not reduce overall mortality for the whole patient group, certain sub-groups showed benefits including those with prolonged neutropenia and recipients of stem cell transplantation. In conclusion, there appears to be evidence supporting the use of systemic antifungal drugs, particularly in patients with more severe/prolonged immune suppression. In the last decade, most attention has been focused on the azoles fluconazole and itraconazole in this regard. The use of conventional amphotericin B is limited by its highly toxic profile and need for intravenous administration. Lipid-associated amphotericin B usage is limited by its high cost and relative lack of clinical data in the prophylactic setting. Inhalation of nebulized amphotericin B was shown not to be effective in preventing aspergillosis in one randomized trial in neutropenic patients.13 Prophylaxis of SFIs Which azole should be used for prophylaxis? The rationale for adopting a prophylactic strategy for SFIs includes: (i) the risk of developing SFI may exceed 10% in certain patients groups; (ii) the high attributable mortality of such infections (especially moulds); (iii) the high cost of treating established and suspected infections; (iv) recurrent infection is common if the patient requires and receives further immunosuppressive therapy; (v) environmental control, e.g. by air filtration is only partially successful in reducing the incidence of invasive aspergillosis. Infections may still occur presumably as a result of transmission via other sources, e.g. water or food and possibly by colonization of sinuses/airways prior to admission for treatment.11 Environmental control may also be impractical or impossible in recipients of allogeneic stem cell transplant and in whom T cell-based immune suppression is very prolonged, far exceeding the initial neutropenic episode. Fluconazole fulfils some of the criteria for an ideal prophylactic agent including availability in oral and intravenous formulations, high bioavailability in oral administration, few side effects and relatively low cost of administration. A recent pharmacy-based survey of major centres in the USA showed that this drug is widely used in the prophylactic setting in haematology patients.14 Its use is supported by two randomized studies against placebo.15,16 An updated report of the Slavin study,17 which focused on recipients of allogeneic stem cell transplantation, shows a long-term benefit in terms of survival for patients receiving fluconazole. However, the main limitation of fluconazole prophylaxis is its limited spectrum of activity. The clinical benefit is limited to a reduction in infection by Candida albicans. Furthermore, there is evidence that the use of fluconazole in this setting may lead to an increase in colonization and infection rates by Candida species other than C. albicans.4,18 Fluconazole has little or no activity against Aspergillus and other mould infections. Itraconazole is available in three formulations: oral capsule, oral solution and intravenous. Clinical use of the oral capsule formulation is limited by relatively poor absorption and bioavailability. To a large extent, these problems have been overcome with the introduction of the oral solution formulation which is cyclodextrin based. There is, however, a potential for increased side effects with this formulation including nausea and diarrhoea, which may influence compliance. There is also the potential for more drug interactions with itraconazole compared with fluconazole. The overriding advantage of itraconazole over fluconazole is its broader spectrum of activity, which includes Aspergillus species and nonalbicans Candida. Early studies of itraconazole in a prophylactic setting focused mainly on patients who received chemotherapy for haematological malignancies with short periods of neutropenia. Itraconazole has been compared against placebo, polyenes and fluconazole in this regard.19–21 The conclusions from these studies have been hampered by the low absolute incidences of SFIs, particularly aspergillosis in these patient groups. Recently however, itraconazole has been compared with fluconazole in two trials focusing on patients at highest risk for Aspergillus infections, i.e. recipients of allogeneic stem cell transplantation. In the Which drug should be used for prophylaxis? Characteristics of the ideal drug for prophylaxis against SFIs would include: (i) a broad spectrum of cover including Candida albicans and non-albicans, Aspergillus species and other moulds; (ii) proven efficacy in this setting; (iii) available orally with high bioavailability; (iv) available in intravenous formulation especially if problems with compliance or bioavailability are anticipated following oral administration; (iv) acceptable toxicity profile; (v) few drug interactions; (vi) low cost. Although there is no drug currently available which fulfils all of these criteria, recent evidence does support the use of systemically active agents in this setting. Which class of drug should be used for prophylaxis? The meta-analysis by Bow et al.12 included randomized controlled trials of the azoles fluconazole, itraconazole, ketoconazole and miconazole or intravenous amphotericin B formulations compared with placebo, no treatment or oral polyenes in severely neutropenic i50 Itraconazole and systemic fungal infection study by Winston et al.,22 itraconazole was compared with fluconazole from day 1 until day 100 after transplantation. Both drugs were allowed to be given intravenously and/or orally. Both were well tolerated though the incidence of gastrointestinal side effects was higher in the itraconazole group. Importantly, whilst the overall mortality was similar in each group of patients, there were fewer invasive fungal infections caused by yeasts and moulds in the itraconazole arm and this translated into a reduced fungusattributable mortality. Discontinuations due to adverse events or death were higher in the itraconazole arm. In a larger study of allogeneic stem cell transplant recipients randomized to receive fluconazole or itraconazole (oral solution/intravenous) for 180 days post-transplant,23 an intention-to-treat analysis showed that fewer patients in the itraconazole arm developed invasive fungal infections during the treatment period (15% fluconazole versus 7% itraconazole; P = 0.03). The benefit was confined to invasive mould infections. There was no difference in overall or fungus-free survival in this study. There was more toxicity including gastrointestinal and hepatic in the itraconazole arm and this led to a higher rate of discontinuation from treatment (36% versus 16%; P < 0.001). Further evidence supporting itraconazole in the prophylactic setting is provided by the meta-analysis by Glasmacher et al.24 Importantly, this study showed that itraconazole was only active in doses equivalent to at least 200 mg per day of bioavailable drug (i.e. at least 400 mg per day oral solution or 200 mg per day intravenous solution). At this bioavailable dose, the rate of fungal infection mortality was reduced by 42% and invasive aspergillosis by 48% on average. Voriconazole shares with itraconazole a broad spectrum of activity against a wide range of Candida and Aspergillus species. Like itraconazole, it is also available in intravenous, oral capsule and oral solution formulations. Bioavailability following oral administration is excellent and compliance good, though a proportion of patients develop visual side effects which are reversible following discontinuation of the drug. Drug interactions are similar to those seen with itraconazole, though more data are required with regard to certain drugs, e.g. vincristine, cyclophosphamide and other cancer chemotherapy agents. It is generally considered that measurement of plasma levels of voriconazole is not required on a routine clinical basis. However, few pharmacokinetic data are available compared with itraconazole and further studies are required examining possible associations between voriconazole levels, toxicity and efficacy. Clinical studies of voriconazole for primary or secondary prophylaxis of invasive fungal infections are under way. Which patients require azole prophylaxis? There have been several attempts at risk stratification of patients (reviewed in Ref. 25). Clearly, the risk of infection increases with both the severity and duration of neutropenia following chemotherapy. The situation in recipients of allogeneic stem cell transplantation is more complex, however. Late SFIs are common in non-neutropenic patients and are associated with the development of graft versus host disease (GVHD) and the use of corticosteroids.26,27 Therefore it is difficult to define exact patient groups who may benefit from prophylaxis and in part this may depend on perceptions of the cost-effectiveness of this approach. One pragmatic solution would be to suggest prophylaxis to patient groups with an expected incidence of SFI of greater than 5%. This would include patients requiring intensive chemotherapy for the treatment of acute leukaemias and those undergoing allogeneic stem cell transplantation but may exclude patients receiving less intense chemotherapy with short durations in neutropenia and recipients of autologous transplantation. Patients who have recovered from an initial SFI but require further chemotherapy/transplantation have a high incidence of reactivation of infection.28 Secondary prophylaxis using systemic antifungal drugs has become a common clinical approach in these patients.29,30 How long should prophylaxis continue for? There are few specific data that address this issue. For patients receiving intensive chemotherapy, it would seem logical to continue prophylaxis for the duration of neutropenia. Invasive fungal infections commonly occur beyond this period in allogeneic stem cell recipients and recent studies have focused on continuing prophylaxis for between 150 and 180 days.22,23 However, patients may require prophylaxis beyond this period should they develop GVHD, especially if prolonged periods of corticosteroid therapy are required. Is loading required when prophylaxis commences? It would seem logical to adopt a loading strategy in high-risk patients. With itraconazole oral suspension, the use of high doses orally is difficult because the cyclodextrin induces nausea and diarrhoea. Two strategies have been shown to be effective. The first includes the use of itraconazole capsules with itraconazole oral suspension for the first few days of prophylaxis.31 The second involves the use of intravenous itraconazole with switching to oral suspension following a short loading period.32 In either case, it is recommended that loading commences following completion of conditioning chemotherapy in the transplant setting due to potential interactions between this azole and chemotherapy agents such as cyclophosphamide.23,33 Intravenous voriconazole may also be used for rapid loading prior to prolonged oral administration.34 Is it important to measure plasma levels of azoles on a routine basis? This would seem to be particularly important with itraconazole and evidence would support improved efficacy in patients obtaining a plasma level of greater than 500 ng/mL.35 High-risk patients in whom such levels are not attained may be offered intravenous itraconazole (e.g. in period of mucositis) or an alternative agent. Available data support switching between intravenous and oral suspension formulations of itraconazole to maintain adequate levels of this drug and its active metabolite.36 Which drug interactions are clinically important in the haematology setting? The main interactions involve the use of itraconazole and voriconazole with rifampicin, ciclosporin A, tacrolimus and certain chemotherapy drugs including vincristine and cyclophosphamide. Rifampicin and other agents which are potent inducers of hepatic i51 Potter microsomal enzymes result in markedly suboptimal levels of itraconazole and in patients receiving these drugs, an alternative antifungal agent would be recommended.37 The effect of rifampicin on itraconazole metabolism is particularly profound and may persist for several weeks after discontinuation. Itraconazole and voriconazole inhibit the metabolism of ciclosporin A and tacrolimus.38,39 Clinicians should be aware of this interaction and reduce the dose accordingly and be guided by regular plasma levels of these medications. A number of reports have indicated that itraconazole may potentiate vincristine-induced neuropathies including severe autonomic neuropathy.40,41 Although specific recommendations have yet to be defined, caution should be exercised in the use of itraconazole prophylaxis in patients receiving protocols where vincristine is administered regularly, e.g. children and adults with acute lymphoblastic leukaemia and certain types of lymphoma. If itraconazole is used in such patients, a wash-out period of several days may be required prior to administration of a vinca alkaloid in order to prevent severe neurotoxicity. Itraconazole has also been implicated in enhancing hepatic toxicity in patients receiving high-dose cyclophosphamide, e.g. stem cell transplant recipients following conditioning treatment. This has been shown to be a result of increased plasma levels of toxic cyclophosphamide metabolites.23,33 Further data are required with respect to voriconazole in this regard. Until further data are available on possible interactions between both azoles and other chemotherapy drugs, particularly those used at high dose, it may be advisable to commence prophylaxis following completion of this treatment, e.g. by a rapid loading strategy. Are there any other concerns with regard to azole prophylaxis? Azoles have limited activity against most non-Aspergillus moulds. Recent reports indicate that the use of azole prophylaxis, particularly voriconazole, may be associated with an increase in the incidence of non-Aspergillus mould infections including species of zygomycete, Fusarium and Scedosporium.42 The exact mechanism whereby azoles may increase the incidences of non-Aspergillus moulds is unknown. One possible explanation is that these infections have occurred in patients with the most prolonged and profound immune suppression who may have succumbed to Aspergillus infections prior to the era of azole prophylaxis. Treatment of invasive fungal infection Evidence is available supporting the use of several agents in this setting, including conventional and lipid-associated amphotericin B, azoles and echinocandins. Few data are available from randomized comparative studies though two such trials have supported the use of voriconazole34 and liposomal amphotericin B46 both against conventional amphotericin B in terms of efficacy in this setting. Central nervous system aspergillosis carries a high mortality. Voriconazole may be the preferred agent in this setting due to its relatively good CNS penetration.47 Caspofungin is a licensed therapy for second-line or salvage therapy of invasive Aspergillus infections.48 Response rates of around 40% have been reported in this difficult group of patients. Conventional and lipidassociated amphotericin B, voriconazole, itraconazole and the echinocandins have a broad spectrum of activity against Candida albicans and non-albicans species. Zygomycoses including Mucor are difficult to treat but amphotericin B/AmBisome may be the preferred agents for these infections.49 Fusarium infections and those caused by certain Scedosporium species may respond to voriconazole treatment.50–52 New approaches to the treatment of fungal infection Although there are a small number of new agents in clinical development, it is likely that most progress will be achieved by novel approaches using existing antifungal agents. Carefully designed clinical trials are required in several areas including: (i) defining optimal approaches to primary and secondary prophylaxis of invasive fungal infections in patients at risk; (ii) evaluating early diagnosis and ‘pre-emptive therapy’ as an alternative to the empirical approach, e.g. by the use of serum PCR or galactomannan detection and/or the early use of high-resolution pulmonary CT scanning; (iii) the use of combination antifungal therapy using agents acting by different mechanisms. The greatest clinical need is in aspergillosis and other mould infections. Early data are encouraging with regard to tolerability and possibly efficacy,53–55 though data from randomized trials are currently lacking for these SFIs; (iv) the modulation of host defences, e.g. the use of growth factors, lymphokines and neutrophil transfusions. Data from well-designed clinical trials in these areas will provide a platform for the development of novel therapeutic strategies in future years. Empirical antifungal therapy This is the setting in which the largest trials of antifungal therapy have been assessed. In recent years, analysis has been based upon a composite end point response with the assessment of both efficacy and toxicity. Available evidence most strongly supports the use of liposomal amphotericin B or caspofungin in this setting.43,44 The use of amphotericin B is hampered by a high incidence of toxic side effects and necessary discontinuations.43 Voriconazole failed to meet the primary end point of non-inferiority in a large randomized trial when compared with liposomal amphotericin B.45 This agent was, however, more effective in reducing the incidences of breakthrough fungal infections. Itraconazole has been compared with amphotericin B in one large randomized study.32 It was found to be equally efficacious and associated with a superior toxicity profile. In patients receiving this agent for prophylaxis however, it would seem logical to change to a different agent in the empirical setting. Transparency declaration M. P. has received fees for speaking on behalf of MSD, Pfizer, Gilead and Ortho Biotech/Janssen-Cilag. He has participated as a member of advisory boards for MSD (caspofungin), Pfizer (voriconazole), Gilead (AmBisome), Elan (Abelcet) and Ortho Biotech/Janssen-Cilag (itraconazole). Further support for research projects has been provided by MSD and Gilead. References 1. Denning DW. Invasive aspergillosis. Clin Infect Dis 1998; 26: 781–803. 2. Martino R, Subira M. Invasive fungal infections in haematology: new trends. Ann Hematol 2002; 81: 233–43. i52 Itraconazole and systemic fungal infection 3. Marr KA, Carter RA, Crippa F et al. Epidemiology and outcome of mould infections in haematopoietic stem cell transplant recipients. Clin Infect Dis 2002; 7: 909–17. 4. Kibbler CC, Seaton S, Barnes RA et al. Management and outcome of bloodstream infections due to Candida species in England and Wales. J Hosp Infect 2003; 54: 18–24. 5. Lin SJ, Schranz J, Teutsch SM. Aspergillosis case-fatality rate: systematic review of the literature. Clin Infect Dis 2001; 32: 358–66. 6. 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