Posaconazole vs. fluconazole or itraconazole prophylaxis in patients with neutropenia

Combination antifungal therapy: what can and should we expect?

Invasive fungal infections are associated with significant morbidity and mortality among immunocompromised patients. Recent advances in antifungal development have afforded us more pharmacologic compounds to choose from when managing these fungal infections. The role of combination antifungal therapy has been well established for fungal infections such as cryptococcal meningitis. The availability of new antifungals, increased incidence of mould infections and high mortality among certain affected populations, such as hematopoietic stem cell transplant recipients, has stimulated interest in the clinical use of combination antifungal therapy. In this paper, we review supporting evidence for the use of combination antifungals in the treatment of cryptococcal meningitis, invasive candidiasis, invasive aspergillosis and zygomycosis. Several controlled clinical trials have demonstrated benefits of combination antifungal approaches for patients with cryptococcal meningitis and invasive candidiasis, but variable effects when using different agents in combination have been reported. Randomized prospective studies of combination antifungal therapy in mould infections are lacking but some series provide supportive evidence for this approach. We also describe limitations of the data and these study designs, including the fact that we still need randomized controlled multicenter studies of combination antifungal therapy for mould infections. Trials in this area should be performed with efficiency and economics in mind, and could potentially use surrogate markers as end points. Therefore, we suggest future investigations of combination antifungal therapy should include a randomized, comparative trial of primary therapy for invasive aspergillosis.

Recent advances in antifungal chemotherapy

For over 50 years, amphotericin B deoxycholate (AmBD) has been the 'gold standard' in antifungal chemotherapy, despite its frequent toxicities. However, improved treatment options for invasive fungal infections (IFIs) have been developed during the last 15 years. Newer antifungal agents, including less toxic lipid preparations of AmBD, triazoles and the echinocandins, have been added to our armamentarium against IFIs. Some of these newer drugs can now replace AmBD as primary therapy (e.g. caspofungin for candidiasis, voriconazole for aspergillosis), whilst others offer new therapeutic options for difficult-to-treat IFIs (e.g. posaconazole for zygomycosis, fusariosis and chromoblastomycosis). It is interesting that extended use of newer antifungals such as fluconazole, despite decreasing the mortality attributed to candidiasis, resulted in selection of species resistant to several antifungals (Candida krusei, Candida glabrata); whilst several publications suggest that prolonged use of voriconazole may expose severely immunocompromised patients to the risk of zygomycosis (breakthrough). On the other hand, the differences in the mode of action of newer antifungals such as echinocandins raise the question whether combination antifungal therapy is more effective than monotherapy. Finally, the availability of an oral formulation with excellent biosafety of several newer antifungals (e.g. posaconazole) makes them candidates for prophylactic or prolonged maintenance therapy.

Fungal infections of the CNS: treatment strategies for the immunocompromised patient

Infections with fungi cause significant morbidity in the immunocompromised host and invasion of the CNS may lead to devastating consequences. Vulnerable individuals include those with haematological malignancies, transplant recipients, and those infected with HIV. Potential pathogens include yeasts, Aspergillus spp., other moulds of an increasing variety, and a range of dimorphic fungi, often associated with particular geographical locations. Antifungal treatments include polyenes such as amphotericin B and its lipid formulations, azoles such as fluconazole and itraconazole, and the more recent voriconazole and posaconazole. The new antifungal class of echinocandins, such as caspofungin, micafungin and anidulafungin, typically lack CNS penetration. Amphotericin B and flucytosine are used to initiate treatment for CNS yeast infections caused by Candida and Cryptococcus neoformans. Voriconazole is preferred for aspergillus, although amphotericin B, particularly in lipid formulation, is also useful. Reliable treatment data are lacking for CNS infections with most of the non-aspergillus moulds; posaconazole holds promise for the zygomycetes and perhaps some of the rarer pigmented fungi, but amphotericin B preparations are still recommended. Oral fluconazole is effective for the CNS manifestations of coccidioides, while histoplasmosis and blastomycoses typically require amphotericin B therapy. Effective treatment requires a definitive diagnosis, which is often challenging in the population at risk of CNS fungal infections.

Posaconazole: a new broad-spectrum antifungal agent

The rising incidence of invasive fungal infections and the emergence of broader fungal resistance have led to the need for novel antifungal agents. Posaconazole is a new member of the triazole class of antifungals. It is available as an oral suspension and has a favorable toxicity profile, has demonstrated clinical efficacy in the treatment of oropharyngeal candidiasis and has shown promise as salvage therapy for invasive aspergillosis, zygomycosis, cryptococcal meningitis and a variety of other fungal infections. In addition, data from randomized controlled studies support its efficacy for use in prophylaxis of invasive fungal infections in patients who are severely immunocompromised. The wide spectrum activity of posaconazole in in vitro studies, animal models and preliminary clinical studies suggest that posaconazole represents an important addition to the antifungal armamentarium.

Invasive aspergillosis in the intensive care unit

Data regarding the incidence of invasive aspergillosis (IA) in the intensive care unit (ICU) are scarce, and the incidence varies. An incidence of 5.8% in a medical ICU has been reported. The majority of patients did not have a hematological malignancy, and conditions such as chronic obstructive pulmonary disease and liver failure became recognized as risk factors. Diagnosis of IA remains difficult. Mechanical ventilation makes it difficult to interpret clinical signs, and radiological diagnoses are clouded by underlying lung pathologies. The significance of a positive respiratory culture result is greatly uncertain, because cultures of respiratory specimens have low sensitivity (50%) and specificity (20%-70%, depending on whether the patient is immunocompromised). The use of serologic markers has never been validated in an ICU population. Limited experience with the detection of galactomannan in bronchoalveolar lavage fluid specimens has yielded promising results. Because of a delay in the diagnosis of IA, the mortality rate exceeds 50%. Recently, our therapeutic armamentarium against IA has improved. Data concerning the safety and efficacy of new antifungal agents in the ICU setting, however, are lacking.

Effects of dosing regimen on accumulation, retention and prophylactic efficacy of liposomal amphotericin B

OBJECTIVES

We hypothesized that effective prophylactic treatment of fungal infections would require adequate drug penetration and retention at potential infection sites. Using a mouse model, we examined liposomal amphotericin B (L-AmB) biodistribution, cell localization and retention in kidneys, lungs, liver and spleen to evaluate effective dosing regimens for prophylaxis of Candida glabrata and Candida albicans infections.

METHODS

Following treatment of mice with cumulative doses of L-AmB (60-225 mg/kg), a bioassay was done to determine tissue drug concentrations 12 h to 6 weeks post-treatment. Immunohistochemical staining with anti-amphotericin B antibodies was used for cellular drug localization. Mice were treated prophylactically with 15-90 mg/kg L-AmB and challenged intravenously 1-7 days later with C. glabrata or they were given a total of 60 mg/kg as daily or intermittent dosing followed by intravenous challenge with C. albicans 3 or 6 weeks later.

RESULTS

On the basis of microg/g tissue, the relative amount of drug was in the order spleen > liver > kidneys > lungs. Amphotericin B levels were maintained above the MIC for many fungi for 1 week in lungs and for as long as 6 weeks in kidneys and spleen. Drug localized in kidney tubular epithelial cells and in macrophages of liver and spleen. In prophylactic models, fungal burden was reduced by several 1000-fold or was undetectable within target tissues (kidneys, spleen).

CONCLUSIONS

These observations underscore the importance of including drug tissue levels to obtain a better understanding of L-AmB efficacy. The sustained concentrations of bioactive AmB in many tissues provide a further rationale for investigating L-AmB prophylactic regimens.

Changing Epidemiology of Rare Mould Infections

There has been an increase in rare mould infections in recent decades. These infections have been reported primarily in severely immunocompromised patients. The emergence of these organisms is multifactorial and can be related to more intense immunosuppression, the prolonged survival of patients who have what were previously fatal diseases, and the selective pressure of broad spectrum antifungal agents used for prophylaxis or therapy. Among these rare mould infections, the Zygomycetes are the most commonly encountered, and in some institutions the increase in these organisms appears to be associated with the use of voriconazole. Aspergillus terreus, a species that is resistant to amphotericin B, and less frequently, A. ustus and A. lentulus, have been noted increasingly as causes of invasive aspergillosis in tertiary care centres in the US. Several species of Scedosporium with innate resistance to many antifungal agents have emerged as major causes of disseminated mould infections that are frequently very difficult to treat. Among patients who have haematological malignancies, are neutropenic or have received a haematopoietic stem cell transplant, infections due to Fusarium species respond poorly to many antifungal agents. Dematiaceous, or brown-black, fungi, most often associated with chronic localised infections, are now increasingly reported as a cause of disseminated infection in immunosuppressed hosts. Concomitant with the increased number of infections with these rare moulds, several new mould-active antifungal agents have been developed. The new expanded spectrum azole, voriconazole, has changed our approach to moulds such as S.apiospermum, Fusarium species and A. terreus that are amphotericin B resistant. Posaconazole, the most recently approved expanded spectrum azole, is the first drug in the azole class to show activity against the Zygomycetes and has proven extremely useful for step-down therapy after initial treatment with amphotericin B. It is not known whether posaconazole is effective as primary therapy for zygomycosis; the use of this agent for that purpose awaits clinical trials with the recently developed intravenous formulation of posaconazole.