Effect of teicoplanin on isolation of Staphylococcus aureus from blood culture media

Neutralization of antimicrobial substances in new BacT/Alert FA and FN Plus blood culture bottles

Time to detection (TTD) in automated blood culture systems is delayed for sensitive microorganisms in the presence of antimicrobial substances and has been associated with worse outcomes for sepsis patients on inadequate empirical therapy. While resin addition removes antimicrobial substances to various degrees from blood culture media, media formulations and the blend of resins may influence performance. The BacT/Alert 3D system (bioMérieux) was investigated using the new resin-containing medium types FA Plus (aerobic) and FN Plus (anaerobic). TTD was compared between control and test bottles containing relevant bacteria or Candida albicans, with and without defined concentrations of antimicrobials. Failure of neutralization was defined as a negative blood culture on day 3. In general, growth delay was nonlinear, concentration dependent, bottle type specific, and reciprocally associated with MICs. Substance-specific serum drug concentrations corresponding to a predefined, clinically relevant 3-h delay of TTD were calculated. Where appropriate, a time interval allowing for drug elimination below this critical level was obtained by pharmacokinetic modeling. Clarithromycin, clindamycin, gentamicin, linezolid, tigecycline, vancomycin, and fluconazole were neutralized. For ciprofloxacin and piperacillin-tazobactam, which were only incompletely neutralized in combination with the most sensitive test strains, a maximum waiting time for blood draw of 1 h was determined based on pharmacokinetics. One or more test strains did not grow in bottles containing either amoxicillin-clavulanate, cefepime, cefotaxime, meropenem, or metronidazole, and we thus recommend particular caution in timing of blood draws if patients have been pretreated with these agents.

Conazoles

This review provides a historical overview of the analog based drug discovery of miconazole and its congeners, and is focused on marketed azole antifungals bearing the generic suffix “conazole”. The antifungal activity of miconazole, one of the first broad-spectrum antimycotic agents has been mainly restricted to topical applications. The attractive in vitro antifungal spectrum was a starting point to design more potent and especially orally active antifungal agents such as ketoconazole, itraconazole, posaconazole, fluconazole and voriconazole. The chemistry, in vitro and in vivo antifungal activity, pharmacology, and clinical applications of these marketed conazoles has been described.

Management of fungal infections following allogeneic stem cell transplantation

Fungal infection remains an important complication in allogeneic stem cell transplantation (allo-SCT). Since the prognosis of fungal infection is poor, prophylaxis is critical for its management; owing to recent progression in allo-SCT management and widespread use of reduced-intensity regimens, the strategy of infectious prophylaxis has also changed. Various antifungals have recently been developed and applied to clinical use. A major change in antifungal management will probably occur in the next few years.

Posaconazole: a next-generation triazole antifungal

Posaconazole is a new drug in the triazole class that has recently been investigated in pivotal Phase III clinical trials. Its antifungal activity is based on the inhibition of the fungal ergosterol synthesis. As demonstrated in vitro, posaconazole exhibits fungicidal activity against Aspergillus spp., Candida spp. and zygomycetes. Currently, posaconazole is only available as an oral suspension. Food consumption affects the bioavailability of posaconazole, while the exposure to posaconazole increases in a dose-proportional manner with a saturation of absorption occurring with a daily dose over 800 mg. Posaconazole is well tolerated without an increase in risk of any treatment-related adverse events during prolonged treatment for 6 or more months (n = 108). Posaconazole has been recently approved by the US FDA and other regulatory bodies for the treatment of oropharyngeal candidiasis, and the prophylaxis of invasive Aspergillus and Candida infections in severely immunocompromised patients. As demonstrated in two pivotal Phase III trials, posaconazole prophylaxis of invasive fungal infection in patients severely immunocompromised by graft-versus-host disease (n = 600) or neutropenia (n = 602) is superior to fluconazole and/or itraconazole prophylaxis. Significantly more patients who received posaconazole, instead of fluconazole, as treatment for oropharyngeal candidiasis sustained clinical success after the treatment was stopped. Preliminary data from a subgroup analysis (n = 24) of two salvage therapy trials for invasive fungal infections, as well as single case reports and series and in vitro studies, suggest that posaconazole might be an attractive oral treatment alternative for zygomycosis.

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.

Posaconazole: clinical pharmacology and potential for management of fungal infections

Posaconazole is a novel lipophilic antifungal triazole that inhibits cytochrome P450-dependent 14-alpha demethylase in the biosynthetic pathway of ergosterol. Inhibition of this enzyme leads to an accumulation of toxic 14-alpha methylsterols and a depletion of ergosterol, resulting in a perturbation of the function of the fungal cell membrane and blockage of cell growth and division. In vitro, posaconazole has potent and broad-spectrum activity against opportunistic, endemic and dermatophytic fungi. This activity extends to organisms that are often refractory to existing triazoles, amphotericin B or echinocandins, such as Candida glabrata, Candida krusei, Aspergillus terreus, Fusarium spp. and the Zygomycetes. A large variety of animal models of invasive fungal infections have provided consistent evidence of efficacy against these organisms in vivo, both in normal and immunocompromised animals. Posaconazole is available as an oral suspension and optimal exposure is achieved when the drug is administered in two to four divided doses along with food or a nutritional supplement. The compound has a large volume of distribution, in the order of 5 l/kg, and a half-life of approximately 20 h. Posaconazole is not metabolized to a significant extent through the cytochrome P450 enzyme system and is primarily excreted in an unchanged form in the feces. Although it is inhibitory, cytochrome P3A4 has no effect on 1A2, 2C8, 2C9, 2D6 and 2E1 isoenzymes, and therefore, a limited spectrum of drug-drug interactions can be expected. Pharmacokinetic studies in special populations revealed no necessity for dosage adjustment based on differences in age, gender, race, renal or hepatic function. Posaconazole has demonstrated strong antifungal efficacy in Phase II and III clinical trials in immunocompromised patients with oropharyngeal and esophageal candidiasis. Posaconazole also showed promising efficacy as salvage therapy in a large Phase II study including 330 patients with invasive fungal infections intolerant to or refractory to standard therapies. Posaconazole appears to be well tolerated in a manner comparable with that of fluconazole and it is currently under regulatory review in the USA and Europe for the treatment of refractory invasive fungal infections. This drug profile reviews the preclinical and clinical pharmacology of posaconazole and its potential role for prevention and treatment of invasive fungal infections.

Emerging azole antifungals

Systemic and superficial fungal infections have progressively emerged over the past few decades as an increasing cause of human disease, especially in the immunocompromised host. Control of fungal disease has proved difficult because few risk factors are potentially preventable; the population at highest risk for fungal disease, the immunocompromised patient, has been steadily increasing. There is a clear need for additional safe and effective therapeutic agents for the treatment of systemic fungal disease. A new generation of triazoles that includes voriconazole, posaconazole, ravuconazole and albaconazole has emerged and are presently in different phases of clinical investigation. These new triazoles have demonstrated a broad spectrum of activity, in particular against fungal pathogens previously resistant to previously available antifungals. This review highlights the emerging azole antifungals, both those available and in clinical development, and discusses their prospects for the future.

New agents for the treatment of systemic fungal infections – current status

Systemic antifungal chemotherapy is enjoying its most dynamic era. More antifungal agents are under development than ever before, including agents in entirely new classes. Major goals of current investigations are to identify compounds with a wide spectrum of activity, minimal toxicity and a high degree of target specificity. The antifungal drugs in development include new azoles {voriconazole, posaconazole (formerly SCH-56592), ravuconazole (formerly BMS-207147)}, lipid formulations of amphotericin B, a lipid formulation of nystatin, echinocandins {anidulafungin (formerly, LY-303366, VER-002), caspofungin (formerly MK-991), micafungin (formerly FK-463)}, antifungal peptides other than echinocandins, and sordarin derivatives. This discussion reviews the currently available antifungal agents and summarises the developmental issues that surround these new systemic antifungal drugs.

Management of rare fungal infections

PURPOSE OF REVIEW

Fungal infections caused by rare fungi have increased in recent years. This may be due to the increase in the number of immunocompromised patients. Some rare fungi are geographically restricted, but with globalization and travel these infections are seen worldwide. The aim of this review is to address recent advances in the management of some uncommon fungal infections.

RECENT FINDINGS

Dematiaceous fungi (Phaeohyphomycetes) have been reported in both immunocompromised and immunocompetent individuals. Cerebral involvement and disseminated disease are associated with high mortality rates. Surgical excision and broad-spectrum triazole antifungal therapy are associated with better outcomes. Mucormycosis in diabetic and immune-suppressed patients is associated with high mortality. Early radical surgical debridement and amphotericin B-based regimens are a key to success. Basidiobolomycosis has recently been reported to cause chronic granulomatous infection of the gastrointestinal tract. Treatment with itraconazole and surgical resection is associated with favourable outcomes. Invasive fusariosis in cancer patients is typically resistant to most antifungal agents, but recent data have suggested a response to voriconazole. Voriconazole also demonstrated activity against Scedosporium apiospermum, but was less active against Scedosporium prolificans. Amphotericin B and itraconazole are currently the treatments of choice for the southeast Asian fungus, Penicillium marneffie.

SUMMARY

Parallel to the increased number of patients susceptible to invasive infections has been an increase in the number of broad-spectrum antifungal agents allowing for better therapeutic options. High-quality data are lacking because of the rarity of such infections. In future, new triazoles and echinocandins will probably replace amphotericin B as the first therapeutic choice for many uncommon fungal infections.

Cutaneous infection by Fusarium species in healthy and immunocompromised hosts: implications for diagnosis and management

Infections by Fusarium species frequently involve the skin, either as the primary or the metastatic site. To better understand the pathophysiology of these infections, 43 new patients with fusariosis were evaluated, and the literature was reviewed. A total of 259 patients (232 immunocompromised and 27 immunocompetent) were identified. Skin involvement was present in 70% of patients, particularly in immunocompromised patients (72% vs. 52%; P=.03). In immunocompetent patients, cutaneous infections were characterized by preceding skin breakdown, localized involvement, slow pace of progression, and good response to therapy. In contrast, skin involvement in immunocompromised patients was only occasionally preceded by skin breakdown and typically was presented as rapidly progressive disseminated lesions at various stages of evolution. Metastatic skin lesions were associated with fungemia, neutropenia, and death. Skin was the single source of diagnosis for the majority of immunocompromised and immunocompetent patients. Recommendations for the prevention of fatal fusariosis originating from skin are presented.

Novel triazole antifungal agents

The risk of opportunistic infections is greatly increased in patients who are immunocompromised due to AIDS, cancer chemotherapy and organ or bone marrow transplantation. Candida albicans is often associated with serious systemic fungal infections, however other Candida species such as Candida krusei, Candida tropicalis and Candida glabrata, as well as Cryptococcus neoformans and filamentous fungi such as Aspergillus, have also emerged as clinically significant fungal pathogens. Two triazole antifungal agents, fluconazole and itraconazole, were introduced over a decade ago and since then have been used extensively for the prophylaxis and treatment of a variety of fungal infections. Although both drugs are effective and have their place in therapy, limitations regarding the utility of these agents do exist. For example, fluconazole is not effective for the prophylaxis or treatment of Aspergillus species and has limited activity against C. krusei and C. glabrata. The use of itraconazole has been limited secondary to concerns regarding unpredictable bioavailability. The rising incidence of fungal infections and the reported increase of non-albicans candidal infections noted over the past two decades highlight the need for new antifungal agents with improved spectra of activity. Several new triazole agents are in various phases of preclinical and clinical trials and may be available for human use in the near future. Three such agents voriconazole, posaconazole and ravuconazole are reviewed and compared with existing agents.

Emerging fungal pathogens: evolving challenges to immunocompromised patients for the twenty-first century

Opportunistic fungi have emerged during the past decade as important causes of morbidity and mortality in immunocompromised patients. Candida species constitute the third to fourth most common causes of nosocomial blood stream infections, and Aspergillus species have emerged as the most common infectious cause of pneumonic mortality in bone marrow/stem cell transplant recipients. Among HIV-infected patients, meningoencephalitis due to Cryptococcus neoformans ranks among the most common AIDS-defining infections. Hyaline septated filamentous fungi, such as Fusarium species, Acremonium species, Paecilomyces species, and Trichoderma species, are increasingly reported as causing invasive mycoses refractory to conventional therapy. Dematiaceous septated filamentous fungi, such as Pseudallescheria boydii, Bipolaris species, and Cladophialophora bantiana cause pneumonia, sinusitis, and CNS infection unresponsive to current therapy. An increasing number of different members of the class of Zygomycetes are reported as causing lethal infections, despite aggressive medical and surgical interventions. Yet the treatment for zygomycosis has not changed in approximately 40 years. The prevalence of the endemic mycoses, such as those due to Penicillium marneffei, Coccidioides immitis, and Histoplasma capsulatum, has been reported to expand rapidly in response to environmental exposures and increased numbers of vulnerable hosts in endemic regions of the world. Dermatophytoses are occurring with increasing prevalence and morbidity in elderly and immunocompromised patients. As we enter the next millennium, we may anticipate that emergent fungal infections will continue to develop in the settings of permissive environmental conditions, selective antifungal pressure, and an expanding population of immunocompromised hosts.