Isavuconazole: A New Broad-Spectrum Triazole Antifungal Agent

Practice Guidelines for the Diagnosis and Management of Aspergillosis: 2016 Update by the Infectious Diseases Society of America

It is important to realize that guidelines cannot always account for individual variation among patients. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations. IDSA considers adherence to these guidelines to be voluntary, with the ultimate determination regarding their application to be made by the physician in the light of each patient's individual circumstances.

Pediatric Invasive Aspergillosis

Invasive aspergillosis (IA) is a disease of increasing importance in pediatrics due to growth of the immunocompromised populations at risk and improvements in long-term survival for many of these groups. While general principles of diagnosis and therapy apply similarly across the age spectrum, there are unique considerations for clinicians who care for children and adolescents with IA. This review will highlight important differences in the epidemiology, clinical manifestations, diagnosis, and therapy of pediatric IA.

Chronic Pulmonary Aspergillosis-Where Are We? and Where Are We Going?

Chronic pulmonary aspergillosis (CPA) is estimated to affect 3 million people worldwide making it an under recognised, but significant health problem across the globe, conferring significant morbidity and mortality. With variable disease forms, high levels of associated respiratory co-morbidity, limited therapeutic options and prolonged treatment strategies, CPA is a challenging disease for both patients and healthcare professionals. CPA can mimic smear-negative tuberculosis (TB), pulmonary histoplasmosis or coccidioidomycosis. Cultures for Aspergillus are usually negative, however, the detection of Aspergillus IgG is a simple and sensitive test widely used in diagnosis. When a fungal ball/aspergilloma is visible radiologically, the diagnosis has been made late. Sometimes weight loss and fatigue are predominant symptoms; pyrexia is rare. Despite the efforts of the mycology community, and significant strides being taken in optimising the care of these patients, much remains to be learnt about this patient population, the disease itself and the best use of available therapies, with the development of new therapies being a key priority. Here, current knowledge and practices are reviewed, and areas of research priority highlighted.

Isavuconazole in the treatment of invasive aspergillosis and mucormycosis infections

We have a limited arsenal with which to treat invasive fungal infections caused by Aspergillus and Mucorales. The morbidity and mortality for both pathogens remains high. A triazole antifungal, isavuconazole, was recently granted approval by the US Food and Drug Administration and the European Medicines Agency for the treatment of invasive aspergillosis and mucormycosis. A randomized double-blind comparison trial for the treatment of invasive aspergillosis found isavuconazole noninferior to voriconazole. A separate, open-label study evaluating the efficacy of isavuconazole in the treatment of mucormycosis found comparable response rates to amphotericin B and posaconazole treated historical controls. The prodrug isavuconazonium sulfate is commercially available in both an oral and intravenous formulation and is generally well tolerated. Isavuconazole’s broad spectrum of activity, limited side effect profile, and favorable pharmacokinetics will likely solidify its place in therapy.

Aspergillus fumigatus-Related Species in Clinical Practice

Aspergillus fumigatus is the main etiologic agent of invasive aspergillosis (IA). Other Aspergillus species belonging to the section Fumigati (A. fumigatus complex) may occasionally be the cause of IA. These strains are often misidentified, as they cannot be distinguished from A. fumigatus by conventional morphological analysis and sequencing methods. This lack of recognition may have important consequences as these A. fumigatus-related species often display some level of intrinsic resistance to azoles and other antifungal drugs. A. lentulus, A. udagawae, A. viridinutans, and A. thermomutatus (Neosartorya pseudofischeri) have been associated with refractory cases of IA. Microbiologists should be able to suspect the presence of these cryptic species behind a putative A. fumigatus isolate on the basis of some simple characteristics, such as defect in sporulation and/or unusual antifungal susceptibility profile. However, definitive species identification requires specific sequencing analyses of the beta-tubulin or calmodulin genes, which are not available in most laboratories. Multiplex PCR assays or matrix-assisted laser desorption ionization - time-of-flight mass spectrometry (MALDI-TOF MS) gave promising results for rapid and accurate distinction between A. fumigatus and other Aspergillus spp. of the section Fumigati in clinical practice. Improved diagnostic procedures and antifungal susceptibility testing may be helpful for the early detection and management of these particular IA cases.

Pharmacokinetics and Concentration-Dependent Efficacy of Isavuconazole for Treatment of Experimental Invasive Pulmonary Aspergillosis

We studied the pharmacokinetics and efficacy of the broad-spectrum triazole isavuconazole for the treatment of experimental invasive pulmonary aspergillosis (IPA) in persistently neutropenic rabbits. Treatment started 24 h after endotracheal administration of Aspergillus fumigatus inoculum; study subjects included rabbits receiving orally administered prodrug isavuconazonium sulfate (BAL8557) equivalent to active moiety isavuconazole (ISA; BAL4815) at 20 (ISA20), 40 (ISA40), and 60 (ISA60) mg/kg (of body weight)/day, with an initial loading dose of 90 mg/kg (ISA90), and untreated rabbits (UC). There were significant concentration-dependent reductions of residual fungal burden (log CFU/gram) and of organism-mediated pulmonary injury, lung weights, and pulmonary infarct scores in ISA40- and ISA60-treated rabbits in comparison to those of UC (P < 0.001). ISA20-treated (P < 0.05), ISA40-treated, and ISA60-treated (P < 0.001) rabbits demonstrated significantly prolonged survival in comparison to that of UC. ISA40- and ISA60-treated animals demonstrated a significant decline of serum (1→3)-β-d-glucan levels (P < 0.05) and galactomannan indices (GMIs) during therapy following day 4 in comparison to progressive GMIs of UC (P < 0.01). There also were significantly lower concentration-dependent GMIs in bronchoalveolar lavage (BAL) fluid from ISA40- and ISA60-treated rabbits (P < 0.001). There was a direct correlation between isavuconazole plasma area under the concentration-time curve from 0 to 24 h (AUC0-24) and residual fungal burdens in lung tissues, pulmonary infarct scores, and total lung weights. In summary, rabbits treated with isavuconazole at 40 and 60 mg/kg/day demonstrated significant dose-dependent reduction of residual fungal burden, decreased pulmonary injury, prolonged survival, lower GMIs in serum and BAL fluid, and lower serum (1→3)-β-d-glucan levels.

Azole Resistance in Aspergillus fumigatus: Can We Retain the Clinical Use of Mold-Active Antifungal Azoles?

Azole resistance in Aspergillus fumigatus has emerged as a global health problem. Although the number of cases of azole-resistant aspergillosis is still limited, resistance mechanisms continue to emerge, thereby threatening the role of the azole class in the management of diseases caused by Aspergillus. The majority of cases of azole-resistant disease are due to resistant A. fumigatus originating from the environment. Patient management is difficult due to the absence of patient risk factors, delayed diagnosis, and limited treatment options, resulting in poor treatment outcome. International and collaborative efforts are required to understand how resistance develops in the environment to allow effective measures to be implemented aimed at retaining the use of azoles both for food production and human medicine.

In Vitro Activity of Isavuconazole and Comparators against Clinical Isolates of the Mucorales Order

The in vitro activity of isavuconazole against Mucorales isolates measured by EUCAST E.Def 9.2 and CLSI M38-A2 methodologies was investigated in comparison with those of amphotericin B, posaconazole, and voriconazole. Seventy-two isolates were included: 12 of Lichtheimia corymbifera, 5 of Lichtheimia ramosa, 5 of group I and 9 of group II of Mucor circinelloides, 9 of Rhizomucor pusillus, 26 of Rhizopus microsporus, and 6 of Rhizopus oryzae. Species identification was confirmed by internal transcribed spacer (ITS) sequencing. EUCAST MICs were read on day 1 (EUCAST-d1) and day 2 (EUCAST-d2), and CLSI MICs were read on day 2 (CLSI-d2). Isavuconazole MIC50s (range) (mg/liter) by EUCAST-d1, CLSI-d2, and EUCAST-d2 were 1 (0.125 to 16), 1 (0.125 to 2), and 4 (0.5 to >16), respectively, across all isolates. The similar values for comparator drugs were as follows: posaconazole, 0.25 (≤ 0.03 to >16), 0.25 (0.06 to >16), and 1 (0.06 to >16); amphotericin, 0.06 (≤ 0.03 to 0.5), 0.06 (≤ 0.03 to 0.25), and 0.125 (≤ 0.03 to 1); voriconazole, 16 (2 to >16), 8 (1 to >16), and >16 (8 to >16), respectively. Isavuconazole activity varied by species: Lichtheimia corymbifera, 1 (0.5 to 2), 1 (1 to 2), and 2 (1 to 4); Lichtheimia ramosa, 0.25 (0.125 to 0.5), 1 (0.5 to 2), and 2 (0.5 to 4); Rhizomucor pusillus, 0.5 (0.5 to 1), 1 (0.125 to 1), and 2 (1 to 2); Rhizopus microsporus, 1 (0.5 to 4), 0.5 (0.125 to 1), and 4 (1 to 8); and Rhizopus oryzae, 1 (0.5 to 4), 1 (0.125 to 2), and 4 (0.5 to 8), respectively, were more susceptible than Mucor circinelloides: group I, 8 (4 to 8), 4 (2 to 4), and 16 (2 to 16), respectively, and group II, 8 (1 to 16), 8 (1 to 8), and 16 (4 to >16), respectively. This was also observed for posaconazole. The essential agreement was best between EUCAST-d1 and CLSI-d2 (75% to 83%). Isavuconazole displayed in vitro activity against Mucorales isolates with the exception of Mucor circinelloides. The MICs were in general 1 to 3 steps higher than those for posaconazole. However, in the clinical setting this may be compensated for by the higher exposure at standard dosing.