Efficacy of FK463, a new lipopeptide antifungal agent, in mouse models of pulmonary aspergillosis

Comparative Pharmacodynamics of Echinocandins against Aspergillus fumigatus Using an In Vitro Pharmacokinetic/Pharmacodynamic Model That Correlates with Clinical Response to Caspofungin Therapy: Is There a Place for Dose Optimization?

Echinocandins have been used as primary therapy of invasive aspergillosis (IA), with suboptimal results at standard dosing. Here, we explored the efficacy of dose escalation in a validated in vitro pharmacokinetic/pharmacodynamic (PK/PD) model. Six echinocandin wild-type (WT) and three non-WT A. fumigatus isolates were tested in an in vitro PK/PD model simulating anidulafungin, caspofungin, and micafungin exposures with a free drug maximum concentration (fCmax) of 0.01 to 16 mg/liter and a half-life (t1/2) of 8 to 22 h. The relationship between the area under the dosing interval time-free drug concentration curve (fAUC0-24)/minimum effective concentration (MEC) and % aberrant mycelium formation was analyzed. PK/PD indices associated with 50 to 99.99% maximal activity (EI50 to EI99.99) were correlated with the clinical outcome of a 50-mg/day standard dose of caspofungin. The probability of target attainment (PTA) was calculated for different dosing regimens of each echinocandin via Monte Carlo analysis. A sigmoidal PK/PD relationship was found for WT isolates with EI99 values of 766, 8.8, and 115 fAUC0-24/CLSI MEC for anidulafungin, caspofungin, and micafungin, respectively. No aberrant mycelia were observed for non-WT isolates, irrespective of their MEC and drug exposure. The EI99, EI99.9, and EI99.99 values corresponded to 2-, 3-, and 4-log10 formation of aberrant mycelia and correlated with survival, favorable, and complete response rates to caspofungin primary therapy in patients with IA. A very low PTA (<13%) was found for the standard doses of all echinocandins, whereas a PTA of ≥90% was found with 100 and 150 mg/day of caspofungin and 1,400 mg/day micafungin against WT isolates. For anidulafungin, the PTA for 1,500 mg/day was 10%. Among the three echinocandins, only caspofungin at 2 or 3 times the licensed dosing was associated with a high PTA. Caspofungin dose escalation might deserve clinical validation.

Antifungal drugs: An updated review of central nervous system pharmacokinetics

Invasive fungal infections (IFIs) in the central nervous system (CNS) are particularly hard to treat and are associated with high morbidity and mortality rates. Four chemical classes of systemic antifungal agents are used for the treatment of IFIs (eg meningitis), including polyenes, triazoles, pyrimidine analogues and echinocandins. This review will address all of these classes and discuss their penetration and accumulation in the CNS. Treatment of fungal meningitis is based on the antifungal that shows good penetration and accumulation in the CNS. Pharmacokinetic data concerning the entry of antifungal agents into the intracranial compartments are faulty. This review will provide an overview of the ability of systemic antifungals to penetrate the CNS, based on previously published drug physicochemical properties and pharmacokinetic data, for evaluation of the most promising antifungal drugs for the treatment of fungal CNS infections. The studies selected and discussed in this review are from 1990 to 2019.

ASP2397 Is a Novel Natural Compound That Exhibits Rapid and Potent Fungicidal Activity against Aspergillus Species through a Specific Transporter

Current therapies against invasive pulmonary aspergillosis (IPA) have a limited cure rate. Given that a delay in treatment initiation may be fatal, a new drug with rapid-onset and potent fungicidal activity is needed. The novel cyclic hexapeptide ASP2397 (currently known as VL-2397) exhibited antifungal activity against Aspergillus fumigatus (including azole-sensitive and azole-resistant isolates), A. terreus, and A. flavus at an MIC range of 1 to 4 μg/ml in human serum. Time-kill curve experiments showed that ASP2397 reduced germinated conidia of A. fumigatus by more than 1 log₁₀ CFU within 6 h. In addition, ASP2397 inhibited hyphal elongation from germinated conidia of A. fumigatus, A. terreus, and A. flavus more rapidly than voriconazole. Under conditions of delayed treatment initiation in an IPA mouse model, ASP2397 had efficacy superior to that of posaconazole, with 100% survival and over 1 log₁₀ CFU/g reduction in lung fungal burden. Histopathological investigation of lungs also showed that ASP2397 markedly suppressed disease progression. To clarify its mechanism of action, we generated a UV-induced mutant of A. fumigatus with low susceptibility to ASP2397. The mutant had a point mutation in the siderophore transporter gene sit1, which is absent in mammalian cells. These findings suggest that ASP2397 may improve clinical treatment options for IPA.

Echinocandins for the Treatment of Invasive Aspergillosis: from Laboratory to Bedside

Echinocandins (caspofungin, micafungin, anidulafungin), targeting β-1,3-glucan synthesis of the cell wall, represent one of the three currently available antifungal drug classes for the treatment of invasive fungal infections. Despite their limited antifungal activity against Aspergillus spp., echinocandins are considered an alternative option for the treatment of invasive aspergillosis (IA). This drug class exhibits several advantages, such as excellent tolerability and its potential for synergistic interactions with some other antifungals. The objective of this review is to discuss the in vitro and clinical efficacy of echinocandins against Aspergillus spp., considering the complex interactions between the drug, the mold, and the host. The antifungal effect of echinocandins is not limited to direct inhibition of hyphal growth but also induces an immunomodulatory effect on the host's response. Moreover, Aspergillus spp. have developed important adaptive mechanisms of tolerance to survive and overcome the action of echinocandins, such as paradoxical growth at increased concentrations. This stress response can be abolished by several compounds that potentiate the activity of echinocandins, such as drugs targeting the heat shock protein 90 (Hsp90)-calcineurin axis, opening perspectives for adjuvant therapies. Finally, the present and future places of echinocandins as prophylaxis, monotherapy, or combination therapy of IA are discussed in view of the emergence of pan-azole resistance among Aspergillus fumigatus isolates, the occurrence of breakthrough IA, and the advent of new long-lasting echinocandins (rezafungin) or other β-1,3-glucan synthase inhibitors (ibrexafungerp).

Echinocandins in antifungal pharmacotherapy

Objectives

Echinocandins are the newest addition of the last decade to the antifungal armamentarium, which, owing to their unique mechanism of action, selectively target the fungal cells without affecting mammalian cells. Since the time of their introduction, they have come to occupy an important niche in the antifungal pharmacotherapy, due to their efficacy, safety, tolerability and favourable pharmacokinetic profiles. This review deals with the varying facets of echinocandins such as their chemistry, in-vitro and in-vivo evaluations, clinical utility and indications, pharmacokinetic and pharmacodynamic profiles, and pharmacoeconomic considerations.

Key findings

Clinical studies have demonstrated that the echinocandins – caspofungin, micafungin and anidulafungin – are equivalent, if not superior, to the mainstay antifungal therapies involving amphotericin B and fluconazole. Moreover, echinocandin regimen has been shown to be more cost-effective and economical. Hence, the echinocandins have found favour in the management of invasive systemic fungal infections.

Conclusions

The subtle differences in echinocandins with respect to their pharmacology, clinical therapy and the mechanisms of resistance are emerging at a rapid pace from the current pool of research which could potentially aid in extending their utility in the fungal infections of the eye, heart and nervous system.

Altered Micafungin Pharmacokinetics in Intensive Care Unit Patients

Micafungin is considered an important agent for the treatment of invasive fungal infections in the intensive care unit (ICU). Little is known on the pharmacokinetics of micafungin. We investigated micafungin pharmacokinetics (PK) in ICU patients and set out to explore the parameters that influence micafungin plasma concentrations. ICU patients receiving 100 mg of intravenous micafungin once daily for suspected or proven fungal infection or as prophylaxis were eligible. Daily trough concentrations and PK curves (days 3 and 7) were collected. Pharmacokinetic analysis was performed using a standard two-stage approach. Twenty patients from the ICUs of four hospitals were evaluated. On day 3 (n = 20), the median (interquartile range [IQR]) area under the concentration-time curve from 0 to 24 h (AUC0-24) was 78.6 (65.3 to 94.1) mg · h/liter, the maximum concentration of drug in serum (Cmax) was 7.2 (5.4 to 9.2) mg/liter, the concentration 24 h after dosing (C24) was 1.55 (1.4 to 3.1) mg/liter, the volume of distribution (V) was 25.6 (21.3 to 29.1) liters, the clearance (CL) was 1.3 (1.1 to 1.5) liters/h, and the elimination half-life (t1/2) was 13.7 (12.2 to 15.5) h. The pharmacokinetic parameters on day 7 (n = 12) were not significantly different from those on day 3. Daily trough concentrations (day 3 to the end of therapy) showed moderate interindividual (57.9%) and limited intraindividual variability (12.9%). No covariates of the influence on micafungin exposure were identified. Micafungin was considered safe and well tolerated. We performed the first PK study with very intensive sampling on multiple occasions in ICU patients, which aided in resolving micafungin PK. Strikingly, micafungin exposure in our cohort of ICU patients was lower than that in healthy volunteers but not significantly different from that of other reference populations. The clinical consequence of these findings must be investigated in a pharmacokinetic-pharmacodynamic (PK-PD) study incorporating outcome in a larger cohort. (This study is registered at ClinicalTrials.gov under registration no. NCT01783379.).

Echinocandin antifungals: review and update

The echinocandins are a new and unique class of antifungal agents that act on the fungal cell wall by way of noncompetitive inhibition of the synthesis of 1,3-beta-glucans. All agents of this class are of parenteral formulation, with no oral preparations available. Caspofungin (Cancidas) was the first approved echinocandin, followed recently by micafungin (Mycamine) and anidulafungin (Eraxis). The precise role of the echinocandins in the antifungal armamentarium is still unfolding. Caspofungin is approved for the treatment of candidal esophagitis and candidemia, salvage therapy of Aspergillus infections and for empirical therapy of febrile neutropenia. Micafungin is likewise approved for candidal esophagitis, in addition to antifungal prophylaxis for hematopoietic stem cell transplant recipients. Anidulafungin is also approved for treatment of candidal esophagitis, as well as therapy of candidemia. There has been anecdotal use of these agents to treat less common fungal pathogens, as well as limited use as a component of combination antifungal therapy. The echinocandins are an important addition to the antifungal armamentarium in the treatment of fungal infections in both immunocompromised patients and those with normal immunity.

Regulation of expression, activity and localization of fungal chitin synthases

The fungal cell wall represents an attractive target for pharmacologic inhibition, as many of the components are fungal-specific. Though targeted inhibition of β-glucan synthesis is effective treatment for certain fungal infections, the ability of the cell wall to dynamically compensate via the cell wall integrity pathway may limit overall efficacy. To date, chitin synthesis inhibitors have not been successfully deployed in the clinical setting. Fungal chitin synthesis is a complex and highly regulated process. Regulation of chitin synthesis occurs on multiple levels, thus targeting of these regulatory pathways may represent an exciting alternative approach. A variety of signaling pathways have been implicated in chitin synthase regulation, at both transcriptional and post-transcriptional levels. Recent research suggests that localization of chitin synthases likely represents a major regulatory mechanism. However, much of the regulatory machinery is not necessarily shared among different chitin synthases. Thus, an in-depth understanding of the precise roles of each protein in cell wall maintenance and repair will be essential to identifying the most likely therapeutic targets.

Intravenous micafungin versus voriconazole for chronic pulmonary aspergillosis: a multicenter trial in Japan

Chronic pulmonary aspergillosis (CPA) is slowly progressive inflammatory pulmonary syndrome due to Aspergillus spp. The evidence regarding CPA treatment is limited. We conducted a randomized, multicenter, open-label trial comparing intravenous micafungin (MCFG) of 150-300 mg once daily with intravenous voriconazole (VRCZ) of 6 mg/kg twice on Day 1 followed by 4 mg/kg twice daily for the treatment of 107 in patients with CPA to compare the efficacy and safety of both drugs as initial treatment in Japan. Treatment effectiveness was defined by clinical, mycological, radiological and serological responses 2 weeks after the initial administration and at the end of therapy. The total of 50 and 47 patients were assigned to the MCFG and VRCZ groups, respectively. The difference in efficacy rates between MCFG and VRCZ was not significant, either after 2 weeks [68.0% vs. 58.7%; the absolute difference, 9.3% with a 95% confidence interval (CI), -9.97 to 28.58, P = 0.344] or at the end of therapy (60.0% vs. 53.2%; the absolute difference, 6.8% with a 95% CI, -12.92 to 26.54, P = 0.499). In the safety evaluation, fewer adverse events occurred in the MCFG than VRCZ group (26.4% vs. 61.1%, P = 0.0004). MCFG was as effective as VRCZ and significantly safer than as an initial treatment of CPA. (UMIN Clinical Trials Registry number, UMIN000001786.).

Clinical effects of micafungin, a novel echinocandin antifungal agent, on systemic fungal infections in surgery, emergency, and intensive-care medicine: evaluation using the AKOTT algorithm

The clinical efficacy of micafungin (MCFG) in surgery, emergency, and intensive-care medicine has been studied in only a limited number of cases. We conducted a multicenter postmarketing study to evaluate MCFG efficacy and safety in Japan. MCFG was given to patients with a temperature exceeding 37.5 degrees C, either with a proven fungal infection based on mycological or histopathological examination, or those who were regarded as having probable or possible fungal infections (patients who had at least one high-risk factor for the development of a systemic fungal infection and for whom fungi had been detected at multiple sites by surveillance culture or a positive beta-D-glucan test). Efficacy was evaluated using the AKOTT algorithm created by our group (AKOTT is an acronym created from the first letter of the surname of each of the five members of the evaluation committee). Of the 180 patients enrolled, 68 were excluded by exclusion criteria or for other reasons, and 112 (58 with proven candidiasis, 1 with proven aspergillosis, and 53 with suspected fungal infection) were evaluated for efficacy. MCFG was administered at a mean daily dose of 104 mg for a mean duration of 14.2 days. It was effective in 72 p 72 patients, ineffective in 28, and the effect was undeterminable in 12, for an overall clinical efficacy 72.0%. MCFG was effective in 78.6% of those with proven candidiasis and in 65.1% with suspected fungal infection, but it was ineffective in the 1 patient with aspergillosis. MCFG eradicated 77.6% (52/67) of fungi isolated. There were 69 drug-related adverse reactions, mainly abnormal hepatic function tests, in 37 of 178 patients evaluated for safety. One adverse reaction, skin eruption, had a probable causal relationship with drug treatment. In conclusion, MCFG had high clinical efficacy and safety in the treatment of deep-seated fungal infections in surgery, emergency, and intensive-care medicine, indicating good potential as a firstline drug for both targeted and empirical therapies.

A Multicenter, Open-Label Clinical Study of Micafungin (FK463) in the Treatment of Deep-seated Mycosis in Japan

The efficacy and safety of micafungin (FK463), which is a new lipopeptide antifungal agent of the echinocandin class and is active against both Aspergillus and Candida species, were investigated in patients with deep-seated mycosis in this study. 70 patients were treated with micafungin 12.5-150 mg/d intravenously for up to 56 d. The overall clinical response rates were 60% (6/10) in invasive pulmonary aspergillosis, 67% (6/9) in chronic necrotizing pulmonary aspergillosis, 55% (12/22) in pulmonary aspergilloma, 100% (6/6) in candidemia, and 71% (5/7) in esophageal candidiasis. The response rates for patients with prior antifungal treatment which was considered ineffective or toxic, were similar to rates for patients without prior treatment. Mycological eradication was observed in patients infected with Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus, Aspergillus niger, Candida albicans, Candida glabrata, or Candida krusei. Adverse events related to micafungin were reported in 21 patients (30%), and there was no dose-related occurrence of any adverse event. It is concluded that treatment with micafungin as monotherapy seems to be effective and safe in patients with deep-seated mycosis.

[Anidulafungin: a new therapeutic approach in antifungal therapy. Pharmacology of anidulafungin]

Anidulafungin is a new echinocandin antifungal agent which inhibits beta-1,3-D-glucan synthase and disrupts fungal cell-wall synthesis. It has marked antifungal activity against Candida spp. and Aspergillus spp., including amphotericin B and triazole resistant strains. Due to the limited oral availability, anidulafungin in clinical use is available for parenteral administration only. Elimination of anidulafungin takes place via slow non-enzymatic degradation to inactive metabolites. Less than 10% and 1% of the initially administered drug is excreted unchanged into feces and urine, respectively. It does not require dosage adjustment in subjects with hepatic or renal impairment established. Anidulafungin is generally well tolerated. Adverse events appear not to be dose or infusion related. The most common treatment related adverse events are phlebitis, headache, nausea, vomiting and pyrexia. The lack of interactions with tacrolimus, cyclosporine and corticosteroids and its limited toxicity profile places anidulafungin as an attractive new option for the treatment of invasive fungal infections especially in transplant patients.

Efficacy of SPK-843, a novel polyene antifungal, in comparison with amphotericin B, liposomal amphotericin B, and micafungin against murine pulmonary aspergillosis

SPK-843, a new polyene antifungal, exhibited dose-dependent efficacy on murine pulmonary aspergillosis models. SPK-843 doses of higher than 1.0 mg/kg of body weight exhibited no renal toxicities and a tendency toward better survival prolongation than the estimated maximum tolerated doses of amphotericin B (Fungizone) (1.0 mg/kg) and liposomal amphotericin B (AmBisome) (8.0 mg/kg).

Comparison of Micafungin and Fluconazole for Experimental Candida Keratitis in Rabbits

PURPOSE

To evaluate the efficacy of subconjunctival injection of micafungin in the treatment of experimental Candida albicans keratitis in rabbits compared with fluconazole.

METHODS

In 1 eye of 24 New Zealand white rabbits, C. albicans (5 x 10 yeast cells) was inoculated in the corneal stroma. The animals were randomly assigned to 3 groups and received subconjunctival injection of 0.5 mL of 0.1% micafungin, 0.2% fluconazole, or physiologic saline once a day for 3 weeks. The eyes were examined slit-lamp biomicroscopically and histopathologically. The clinical course of fungal keratitis was compared among the 3 groups. In another 36 rabbits, a microbiological examination was performed using a quantitative isolate recovery technique, and the numbers of colony-forming units were compared among groups.

RESULTS

The clinical scores were significantly lower in the micafungin group than in the other 2 groups throughout the study period (P < 0.0001 approximately P = 0.0027, Bonferroni multiple comparison). The fluconazole group showed significantly lower clinical scores than the saline group on day 18 (P = 0.0343). At the end of the study period, there were significant differences between the saline and micafungin groups (P < 0.0001), the saline and fluconazole groups (P = 0.0072), and the fluconazole and micafungin groups (P = 0.0013). Histopathologically, similar results were obtained. Moreover, the results of the microbiological examination nearly matched the clinical and histopathologic findings.

CONCLUSIONS

Subconjunctival administration of micafungin was effective in the treatment of experimental Candida keratitis. Local application of micafungin to the eye would be a feasible treatment option for clinical fungal keratitis.

Clinical efficacy of micafungin for chronic pulmonary aspergillosis

The rising incidence of pulmonary aspergillosis is a major clinical concern. However, only a limited number of antifungal drugs are available in Japan that are effective for pulmonary Aspergillus infections. Micafungin (MCFG), a newly developed echinocandin family antifungal drug, has potent antifungal activity in vitro, but few reports detailing its clinical effectiveness have been published to date. A retrospective study was performed using data from nine patients (seven males and two females) with chronic invasive forms of pulmonary aspergillosis, who were treated with either MCFG alone or together with other antifungal drugs between April 2003 and March 2004. The overall efficacy of the treatments was evaluated in the terms of clinical, mycological, serological and radiological responses. The average age of the patients was 61.9 (20-83) years old. Four patients received only MCFG and the remaining five patients were treated with MCFG in combination with amphotericin B (AMB) only (1 patient), itraconazole (ITC) only (2 patients) or AMB backed up by ITC during AMB discontinuation periods (2 patients). The mean duration of MCFG administration was 59.2 (28-96) days. Overall, the treatment was judged to have been effective for seven of nine patients. No patient's condition deteriorated in response to treatment. Administration of MCFG alone was judged to have been effective in three of four patients. No notable adverse effects were documented during MCFG administration. These data suggest that MCFG may be an effective and safe antifungal drug for the treatment of chronic invasive forms of pulmonary aspergillosis.

Antifungal prophylaxis following reduced-intensity stem cell transplantation

Reduced-intensity stem cell transplantation (RIST) has been developed to be a novel curative option for advanced hematologic diseases. Its minimal toxicity allows for transplantation in patients with advanced age or with organ dysfunction. Young patients without comorbidity can undergo RIST as outpatients. However, fungal infection remains an important complication in RIST. Given the poor prognosis of fungal infection, prophylaxis is critical in its management. The prophylactic strategy is recently changing with the development of RIST. Hospital equipment is important for fungal prophylaxis; however, the median day for the development of fungal infection is day 100, when most RIST patients are followed as outpatients. The focus of fungal management after RIST needs to shift from in-hospital equipment to oral antifungals. Various antifungals have recently been developed and introduced for clinical use. A major change in antifungal management will probably occur within several years.

Steady-state pharmacokinetics of micafungin and voriconazole after separate and concomitant dosing in healthy adults

We assessed the pharmacokinetics and interactions of steady-state micafungin (Mycamine) or placebo with steady-state voriconazole in 35 volunteers. The 90% confidence intervals around the least-squares mean ratios for micafungin pharmacokinetic parameters and placebo-corrected voriconazole pharmacokinetic parameters were within the 80%-to-125% limits, indicating an absence of drug interaction.

The echinocandins: comparison of their pharmacokinetics, pharmacodynamics and clinical applications

Caspofungin, micafungin and anidulafungin are three drugs of the echinocandin class of antifungals available for intravenous treatment of invasive candidiasis and aspergillosis. They exhibit high in vitro and in vivo activities against Candida spp. and Aspergillus spp. In various clinical studies investigating candidemia and invasive candidiasis, Candida esophagitis, and fever in neutropenia, the clinical efficacy of the echinocandin tested was similar to that of established antifungals. Antifungal activity against strains no longer susceptible to conventional antifungal agents, such as fluconazole and amphotericin B suggests that echinocandins can be used as salvage therapy in life-threatening fungal infections. There is no cross-resistance to other antifungals. Excellent safety and tolerability of treatment with caspofungin has been documented over a total of 4.3 million patient days. Echinocandins are poor substrates of the cytochrome P450 enzyme family and can be safely co-administered with most drugs without the need for dosage adaptation. No dose reduction is required in renal impairment. A reduction in the daily maintenance dose has been recommended for caspofungin, but not for micafungin and anidulafungin in patients presenting with mild to moderate hepatic failure.

[Fungal infection following reduced-intensity stem cell transplantation (RIST)]

Hematopoietic stem cell transplantation has been established as a curative treatment for advanced hematologic malignancies. Transplantation with a reduced-intensity conditioning regimen has been developed, and the minimal toxicity of reduced-intensity stem cell transplantation (RIST) has made this procedure available for patients of advanced age or with organ dysfunction. The response of malignant lymphoma and some solid tumors to RIST has been observed. RIST with unrelated donors and umbilical cord blood has been studied. Fungal infection is an important complication of RIST. Since the prognosis of fungal infection is poor, the management has been focused on its prophylaxis. Given recent progression in RIST management, the strategy of infectious prophylaxis has also changed. Equipment in the hospital is important for fungal infection; however, the median day of the development of fungal infection is day 100, when most patients are followed as outpatients. The focus of fungal management after RIST is oral antifungal agents rather than in-hospital equipment. Various antifungal agents have recently been developed and applied for clinical use, and many of these have been developed simultaneously for the first time. A major change in antifungal management will probably occur in the next several years.

A study to determine the safety profile and maximum tolerated dose of micafungin (FK463) in patients undergoing haematopoietic stem cell transplantation

This open-label, dose-escalation study assessed the maximum tolerated dose (MTD) of the new antifungal micafungin in patients undergoing haematopoietic stem cell transplantation (HSCT). Participants received 3, 4, 6 or 8 mg/kg/day micafungin intravenously from 7 days to a maximum of 28 days or until neutropaenia resolved. The MTD was defined as the highest dose not causing the same Grade 3 or 4 adverse event in three or more patients. All 36 participants received >/=8 days treatment for a median of 18 days (range: 8-28); 1 patient withdrew consent and a further 11 discontinued to receive another systemic antifungal agent for a suspected infection. No case of confirmed invasive fungal infection occurred. Adverse events were those expected for patients undergoing HSCT and showed no evidence of dose-related toxicity. Criteria for MTD were not met; no patient had a Grade 3 or 4 adverse event considered causally related to micafungin. Thus, the MTD of micafungin can be inferred to be 8 mg/kg/day or higher.

Micafungin (FK463), alone or in combination with other systemic antifungal agents, for the treatment of acute invasive aspergillosis

BACKGROUND

Micafungin (FK463) is a new lipopeptide compound (echinocandin) with activity against Aspergillus and Candida species. This study evaluated the safety and efficacy of micafungin in patients with proven or probable invasive aspergillosis (IA).

METHODS

A multinational, non-comparative study was conducted to examine proven or probable (pulmonary only) Aspergillus species infection in a wide variety of patient populations. The study employed an open-label design utilizing micafungin alone or in combination with another systemic antifungal agent. Criteria for IA and therapeutic responses were judged by an independent panel.

RESULTS

Of the 331 patients enrolled, only 225 met diagnostic criteria for IA as determined by the independent panel and received at least one dose of micafungin. Patients included 98/225 who had undergone hematopoietic stem cell transplantation (HSCT) (88/98 allogeneic), 48 with graft versus host disease (GVHD), and 83/225 who had received chemotherapy for hematologic malignancy. A favorable response rate at the end of therapy was seen in 35.6% (80/225) of patients. Of those only treated with micafungin, favorable responses were seen in 6/12 (50%) of the primary and 9/22 (40.9%) of the salvage therapy group, with corresponding numbers in the combination treatment groups of 5/17 (29.4%) and 60/174 (34.5%) of the primary and salvage treatment groups, respectively. Of the 326 micafungin-treated patients, 183 (56.1%) died during therapy or in the 6-week follow-up phase; 107 (58.5%) deaths were attributable to IA.

CONCLUSIONS

Micafungin as primary or salvage therapy proved efficacious and safe in high-risk patients with IA, although patient numbers are small in the micafungin-only groups.

Micafungin: a new echinocandin

Micafungin, a potent inhibitor of 1,3-beta-D-glucan synthase, has become the second available agent in the echinocandins class that is approved for use in clinical practice. This agent shares with caspofungin an identical spectrum of in vitro activity against Candida albicans, non-albicans species of Candida, and Aspergillus species, as well as several but not all pathogenic molds. If anything, its in vitro activity appears to be superior to that of caspofungin, although the clinical relevance of this observation is unclear. The clinical role of micafungin appears to be similar to that of caspofungin, although clinical data are still lacking at this stage, with initial approval only for treatment of esophageal candidiasis and prophylaxis in subjects with neutropenia. Pharmacokinetic and pharmacodynamic studies and reports of adverse effects and safety have reported similar but not identical results to those of other agents in the echinocandin class. Factors such as acquisition costs and the potential for resistance development may be more relevant to its widespread use than in vitro and in vivo data comparisons with caspofungin.

Comparative efficacies of conventional amphotericin b, liposomal amphotericin B (AmBisome), caspofungin, micafungin, and voriconazole alone and in combination against experimental murine central nervous system aspergillosis

Central nervous system (CNS) aspergillosis is a severe disease that responds poorly to current therapies. The current studies examined the efficacies of several antifungal agents alone or in combination with a murine model of CNS aspergillosis. Immunosuppressed mice were infected intracerebrally with Aspergillus fumigatus and treated with an amphotericin B preparation, an echinocandin, or voriconazole (VCZ) given alone or in combination. Monotherapy studies showed that micafungin (MICA), caspofungin (CAS), VCZ, conventional amphotericin B (AMB), Abelcet (ABLC) (a lipid-carried AMB formulation; Enzon Pharmaceuticals, Inc.), and AmBisome (AmBi) (liposomal AMB; Gilead Sciences, Inc.) were efficacious. However, doses of AmBi above 15 mg/kg of body weight showed reduced efficacy. Neither MICA nor CAS showed dose responsiveness at the doses tested (1, 5, or 10 mg/kg). Only the 40-mg/kg dose of VCZ was effective. AmBi and ABLC showed dose responsiveness, with 10-mg/kg doses causing a significant reduction in fungal burden; they had equivalent activities at the 10-mg/kg dose. Suboptimal dosages of AmBi in combination with MICA, CAS, or VCZ were effective in prolonging survival. However, significantly enhanced activity was demonstrated only with AmBi and VCZ in combination. AmBi in combination with MICA or CAS showed a trend toward enhanced activity, but the combination was not significantly superior to monotherapy. The use of AmBi with CAS or VCZ at optimal doses did not improve efficacy. Cure was not attained with any dosage combinations. These results indicate that AmBi in combination with VCZ may be superior for treatment of CNS aspergillosis; combinations of AmBi and MICA or CAS were not antagonistic and may have a slight benefit.

Efficacy of micafungin alone or in combination against experimental pulmonary aspergillosis

Mortality from invasive pulmonary aspergillosis approaches 80% with few useful therapeutic options available. In these studies, we examined the efficacy of micafungin (MICA) alone or in combination with other antifungals in a model of pulmonary aspergillosis in immunosuppressed DBA/2 mice infected intranasally with conidia of Aspergillus fumigatus 10AF. In the initial study, groups of mice were given saline, or 1, 3 or 10 mg kg(-1) of MICA b.i.d., s.c. All saline controls, and 90% of untreated mice succumbed to infection. The efficacy of MICA was difficult to assess because of an apparent toxicity at 10 mg kg(-1). MICA given at 1 mg/kg significantly prolonged survival over the saline controls (P = 0.008). MICA at 3 or 10 mg kg(-1) versus the saline controls approached significance. No treatment regimen differed in efficacy. The efficacy of combination therapy was assessed, with mice given either no treatment, MICA at 1 mg/kg/dose, 0.8 mg kg(-1) of intravenous amphotericin B (AMB), 100 mg kg(-1) of oral itraconazole (ICZ), or 100 mg/kg/dose of twice-daily subcutaneous nikkomycin Z (NIK). AMB alone and MICA + AMB or MICA +NIK significantly prolonged survival (P < 0.05 - 0.02) over that of the controls. ICZ alone, ICZ+MICA and NIK alone did not significantly prolong survival. MICA alone at 1 mg/kg approached significance in prolonging survival. The combination of MICA and ICZ appeared to be potentially antagonistic. Although AMB+MICA was efficacious, no synergistic activity was noted for any of the regimens. Overall, these results indicate that MICA has moderate activity against pulmonary aspergillosis and might be useful in combination with conventional AMB.

Glucan-associated protein modulations and ultrastructural changes of the cell wall in Candida albicans treated with micafungin, a water-soluble, lipopeptide antimycotic

The composition of glucan-associated proteins (GAP) in the cell wall of Candida albicans was strongly affected by treatment with a sub-MIC yet beta-glucan synthesis inhibitory concentration (0.01 microg/ml) of FK463 (micafungin). Namely, a decrease in enzymes of glucose metabolism (mostly enolase and a novel 40 kDaltons component, here identified as the enzyme fructose-1,6-biphosphate aldolase) was observed, and this was coupled with an increase in two beta1-3 exo-glucanase isoforms (34 and 44 kDa, respectively). No GAP changes were detected in the same strain of the fungus made resistant to the drug, attesting to the specificity of the observed cell wall protein modulation. In addition, GAP changes were accompanied by marked ultrastructural alterations upon treatment with the sub-MIC dose of the drug, the majority of which was an aberrant cell surface morphology and a derangement of the normal layering of the cell wall. Our data demonstrate that sub-MIC doses of micafungin do critically affect not only the beta-glucan synthetic machinery but also protein composition and the whole cell wall structure of Candida albicans.

Electron microscopic findings for micafungin-treated experimental pulmonary aspergillosis in mice

We performed a scanning and transmission electron microscopic study on the efficacy of micafungin (MCFG) to understand what kind of damage MCFG causes to Aspergillus and to confirm its previously reported in vitro killing activity against Aspergillus in a mouse model of pulmonary aspergillosis. Aspergillus hyphae in MCFG-treated mice displayed hyphal burst, evidenced as either flattened or atrophied appearance and leakage of cellular contents after collapse of the cell wall. Thus, MCFG can induce the destruction of Aspergillus hyphae at the focus of infection. The results of the present study indicate that MCFG improves pulmonary aspergillosis due to lethal damage to Aspergillus hyphae. This action can effectively reduce the invasive ability of Aspergillus even though MCFG does not sterilize the fungal burden.

Safety, tolerability, and pharmacokinetics of Micafungin (FK463) in febrile neutropenic pediatric patients

Micafungin (FK463) is a new parenteral echinocandin. A multicenter, phase I, open-label, sequential-group dose escalation study was conducted to assess the safety, tolerability, and pharmacokinetics of micafungin in neutropenic pediatric patients. A total of 77 patients stratified by age (2 to 12 and 13 to 17 years) received micafungin. Therapy was initiated at 0.5 mg/kg per day and escalated to higher dose levels of 1.0, 1.5, 2.0, 3.0, and 4.0 mg/kg per day. Micafungin was administered within 24 h of initiating broad-spectrum antibacterial antibiotics for the new onset of fever and neutropenia. The most common overall adverse events in the study population were diarrhea (19.5%), epistaxis (18.2%), abdominal pain (16.9%), and headache (16.9%). Nine patients (12%) experienced adverse events considered by the investigator to be possibly related to the study drug. The most common related events were diarrhea, vomiting, and headache, all occurring in two patients each. There was no evidence of a dose-limiting toxicity as defined within the prespecified criteria of this clinical protocol. There was one death during the study due to septic shock. The pharmacokinetic profiles for micafungin over the 0.5- to 4.0-mg/kg dose range demonstrated dose linearity. Clearance, volume of distribution, and half-life remained relatively constant over the dose range and did not change with repeated administration. The overall plasma pharmacokinetic profile was similar to that observed in adults. However, there was an inverse relation between age and clearance. For patients 2 to 8 years old, clearance was approximately 1.35 times that of patients >/=9 years of age. In summary, micafungin over a dosage range between 0.5 and 4.0 mg/kg/day in 77 febrile neutropenic pediatric patients displayed linear pharmacokinetics and increased clearance as a function of decreasing age.

Toxicological evaluation of micafungin ophthalmic solution in rabbit eyes

There have been no reports of the topical application of micafungin to the eye. The aim of this study was to evaluate the safety of topical instillation of 0.1% micafungin ophthalmic solution in rabbit eyes. In New Zealand white rabbits (n = 6), 50 microL of 0.1% micafungin solution was topically instilled to 1 eye, and 50 microL of sterile saline was applied to the other eye. Both eyedrops were administered hourly from 7 A.M. for 7 days. Measurements were conducted on corneal thickness, intraocular pressure, endothelial cell density, and lactate dehydrogenase (LDH) activity of tear samples. The eyes were examined slit-lamp biomicroscopically and histopathologically. Topical micafungin application for 1 week did not induce any changes in intraocular pressure, endothelial cell density, and tear LDH. Corneal thickness after instillation was slightly, but significantly, smaller in the micafungin group than in the control group (P = 0.0156, paired t test), but this difference disappeared within 24 hours after the final instillation. Biomicroscopy and histopathology revealed no significant toxic influence of micafungin application on the cornea. Topical instillation of micafungin solution had no apparent toxicity to the cornea. These results warrant future studies on the efficacy of micafungin ophthalmic solution against corneal fungal infection.

Pharmacokinetic and maximum tolerated dose study of micafungin in combination with fluconazole versus fluconazole alone for prophylaxis of fungal infections in adult patients undergoing a bone marrow or peripheral stem cell transplant

In this dose escalation study, 74 adult cancer patients undergoing bone marrow or peripheral blood stem cell transplantation received fluconazole (400 mg/day) and either normal saline (control) (12 subjects) or micafungin (12.5 to 200 mg/day) (62 subjects) for up to 4 weeks. The maximum tolerated dose (MTD) of micafungin was not reached, based on the development of Southwest Oncology Group criteria for grade 3 toxicity; drug-related toxicities were rare. Commonly occurring adverse events considered related to micafungin were headache (6.8%), arthralgia (6.8%), hypophosphatemia (4.1%), insomnia (4.1%), maculopapular rash (4.1%), and rash (4.1%). Pharmacokinetic profiles for micafungin on days 1 and 7 were similar. The mean half-life was approximately 13 h, with little variance after repeated or increasing doses. Mean maximum concentrations of the drug in serum and areas under the concentration-time curve from 0 to 24 h were approximately proportional to dose. There was no clinical or kinetic evidence of interaction between micafungin and fluconazole. Five of 12 patients (42%) in the control group and 14 of 62 (23%) in the micafungin-plus-fluconazole groups had a suspected fungal infection during treatment which resulted in empirical treatment with amphotericin B. The combination of micafungin and fluconazole was found to be safe in this high-risk patient population. The MTD of micafungin was not reached even at doses up to 200 mg/day for 4 weeks. The pharmacokinetic profile of micafungin in adult cancer patients with blood or marrow transplants is consistent with the profile in healthy volunteers, and the area under the curve is proportional to dose.

Micafungin: pharmacology, experimental therapeutics and clinical applications

Invasive fungal infections are important causes of morbidity and mortality in hospitalised patients. Current therapy with amphotericin B and antifungal triazoles has overlapping targets and is limited by toxicity and resistance. Echinocandins are a new class of antifungal drugs, which inhibit the synthesis of 1,3-beta-D-glucan. This homopolysaccharide is an important component of the cell wall of many pathogenic fungi, providing osmotic stability and functioning in cell growth and cell division. Micafungin, which is a member of the echinocandin class, exhibits in vitro fungicidal or fungistatic activity against a variety of fungal pathogens which include Candida and Aspergillus species but not Cryptococcus, Fusarium or Zygomycetes. Micafungin demonstrates linear pharmacokinetics, which are not altered by drugs metabolised through the P450 enzyme system. The preclinical and clinical data strongly support the development of micafungin for treatment of proven or suspected mucosal and invasive Candida infections in immunocompetent and immunocompromised patients. This paper reviews the preclinical and clinical pharmacology of micafungin and its potential role for treatment of fungal invasive infections in patients.

Pharmacological agents in development for invasive aspergillosis

The urgent medical need for new potent antifungal agents in the management of invasive aspergillosis (IA) has resulted in the development of several compounds which may be of value in the future for the treatment or prophylaxis of IA. In the past years, several novel types of drugs have been discovered and developed, some of which are already in late-stage clinical trials and ready to enter the market. This paper discusses the antifungal agents, classified by their mode of action, that are currently available and the agents which are still in development for treatment or prevention of IA.

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.

Value of an inhalational model of invasive aspergillosis

Animal models of invasive aspergillosis have been used for virulence studies and antifungal efficacy evaluations but results have been inconsistent. In an attempt to reproduce human infection, many Aspergillus animal models have utilized a 'pulmonary route' for delivery of conidia, largely through intranasal instillation. However, several radiolabeled particle studies have shown that aerosol delivery is preferable to intranasal instillation to create a more homogenous delivery to the lungs. We hypothesized that an inhalational model would be more robust for studies of invasive aspergillosis pathogenesis and antifungal therapy. We developed an inhalational model of Aspergillus fumigatus infection using a Hinners inhalation chamber and demonstrated by quantitative polymerase chain reaction that this new inhalational model creates a more homogenous murine pneumonia, facilitating analysis of mutant strains and treatment regimens.

Optimal prophylactic dosage and disposition of micafungin in living donor liver recipients

Micafungin, a new candin antifungal drug, has a good safety profile and a significant therapeutic effect against Candida and Aspergillus. Little is known, however, about the optimal prophylactic dosage and the disposition of micafungin in liver transplant recipients, or about the effect of continuous venovenous hemodialysis (CVVH) on the pharmacokinetics of micafungin. Six living donor liver transplant patients were enrolled in this study. The mean C(max) and C(min) (trough) values of micafungin in plasma were 6.31 +/- 1.08 and 1.65 +/- 0.54 microg/mL, respectively. The mean elimination half-life (t(1/2)) and mean area under the curve up to 12 h post-dosing (AUC 0-12 h) were 13.63 +/- 2.77 h and 50.04 +/- 6.48 microg.h/mL, respectively. The concentrations of micafungin at the inlet and outlet of the dialyzer were very similar. The mean (+/-SD) ratio of micafungin concentrations at the inlet and outlet of the dialyzer (coutlet/cinlet) and the clearance of micafungin were 0.96 +/- 0.04 and 0.054 +/- 0.04 mL/min/kg, respectively. The amount in the ultrafiltrate was 1.0 mg. Micafungin effectively prevents systemic fungal infection in patients who have undergone liver transplantation. No significant differences were observed in the disposition of micafungin in recipients, and the therapeutic drug level can be achieved by administration of micafungin at a dosage of 40-50 mg/d. The CVVH had little effect on micafungin kinetics, and no dose adjustment or modification of dosing interval was needed during CVVH.

Micafungin

Micafungin, an echinocandin antifungal agent with a novel mechanism of action, inhibits beta-(1,3)-D-glucan synthase interfering with fungal cell wall synthesis. It shows excellent antifungal activity against a broad range of Candida spp., including azole-resistant strains, and Aspergillus spp. in in vitro and animal studies. In HIV-positive patients, intravenous micafungin 50-150 mg/day dose-dependently eradicated endoscopically confirmed oesophageal candidiasis, with micafungin 100 and 150 mg/day being more effective than micafungin 50 mg/day and as effective as fluconazole 200 mg/day in a double-blind trial. In nonblind trials, micafungin (monotherapy or combination therapy) was effective against invasive aspergillosis, candidiasis and candidaemia in paediatric and adult patients with newly diagnosed or refractory infections. Micafungin 50 mg/day provided significantly better antifungal prophylaxis than fluconazole 400 mg/day in 882 haematopoietic stem cell transplant recipients in a randomised, double-blind trial. Respective overall success rates were 80% and 73.5%. Micafungin is generally well tolerated. Adverse events were not dose- or infusion-related with micafungin 12.5-900 mg/day; no histamine-like reactions occurred. Micafungin was as well tolerated as fluconazole, with numerically fewer micafungin recipients discontinuing treatment (4.2% vs 7.2%).

Successful Micafungin (FK463) Treatment of Invasive Pulmonary Aspergillosis in a Patient with Acute Lymphoblastic Leukemia in a Phase II Study

We treated a 52-year-old woman with acute lymphoblastic leukemia (ALL) who developed invasive pulmonary aspergillosis (IPA) as a result of neutropenia following remission-induction chemotherapy. Although serological test results, such as those for platelia and pastrex, were all negative and the serum level of beta-D-glucan was low, Aspergillus DNA was detected in blood by the polymerase chain reaction method. A clinically documented diagnosis of IPA was made on the basis of chest x-rays, computed tomography scan findings, and the detection of Aspergillus DNA. Micafungin (FK463), a candin class antifungal agent, was administered at a dose of 75 to 150 mg/day, because other antifungal agents were not effective. The increase in serum concentration of micafungin was dose-dependent and was accompanied by improvement of symptoms and objective findings. Micafungin was effective for the treatment of IPA in this patient with ALL.

Combined action of micafungin, a new echinocandin, and human phagocytes for antifungal activity against Aspergillus fumigatus

Micafungin, a new echinocandin, inhibits fungal cell wall beta-glucan synthesis. We postulated micafungin and host phagocytic cells could act together in damaging fungi. Using the metabolic XTT assay, micafungin alone (0.01 and 0.10 microg/ml) inhibited Aspergillus fumigatus germlings by 48% and 61%, respectively. Polymorphonuclear neutrophils (PMNs) inhibited germlings by 53%. Micafungin at 0.01 or 0.10 microg/ml and PMNs resulted in additive inhibition, 82% and 99%, respectively. Monocyte-derived macrophage (MDM) monolayers inhibited germling growth by 66%; micafungin (0.01 or 0.10 microg/ml) alone inhibited by 32% and 42%, respectively. MDMs and micafungin (0.01 or 0.10 microg/ml) caused an additive inhibition of growth, 85% and 95%, respectively. Hyphae were generated by incubation of conidia for 24 h with or without micafungin. PMNs alone, added to hyphae, inhibited growth by 19% in the subsequent 20 h. Hyphae generated in the presence of micafungin (0.10 microg/ml) and subsequently cultured with micafungin for 24 h inhibited growth by 64%. PMNs plus micafungin resulted in 82% inhibition. Monocytes alone inhibited hyphal growth by only 5%. Hyphae produced in the presence of micafungin (0.01 microg/ml) and incubated again with micafungin for 24 h inhibited growth by 47%; combination with monocytes resulted in 62% inhibition. These data indicate that micafungin inhibits growth of tissue forms of A. fumigatus, and phagocytes and micafungin together have an additive effect. These findings support the thesis that the greater efficacy of micafungin in vivo compared with in vitro could be due to combined effect of phagocytic cells and micafungin.

New and emerging antifungal agents: impact on respiratory infections

Fungal pathogens are increasingly important causes of respiratory disease, yet the number of antifungal agents available for clinical use is limited. Use of amphotericin B deoxycholate is hampered by severe toxicity. Triazole agents currently available have significant drug interactions; fluconazole has a limited spectrum of activity and itraconazole was, until recently, available only in oral formulations with limited bioavailability. The development of resistance to all three agents is increasingly being recognized and some filamentous fungi are resistant to the action of all of these agents. In the past few years, new antifungal agents and new formulations of existing agents have become available.The use of liposomal amphotericin B preparations is associated with reduced, but still substantial, rates of nephrotoxicity and infusion-related reactions. An intravenous formulation of itraconazole has been introduced, and several new triazole agents have been developed, with the view of identifying agents that have enhanced potency, broader spectra of action and improved pharmacodynamic properties. One of these, voriconazole, has completed large-scale clinical trials. In addition, caspofungin, the first of a new class of agents, the echinocandins, which inhibit cell wall glucan synthesis, was approved for use in the US in 2001 as salvage therapy for invasive aspergillosis. It is hoped that the availability of these agents will have a significant impact on the morbidity and mortality of fungal respiratory infections. However, at the present time, our ability to assess their impact is limited by the problematic nature of conducting trials for antifungal therapy.