Isavuconazole (BAL4815) Pharmacodynamic Target Determination in an In Vivo Murine Model of Invasive Pulmonary Aspergillosis against Wild-Type and cyp51 Mutant Isolates of Aspergillus fumigatus

Alexander J Lepak; Karen Marchillo; Jamie VanHecker; David R Andes

doi:10.1128/AAC.01355-13

. 2013 Dec;57(12):6284–6289. doi: 10.1128/AAC.01355-13

Isavuconazole (BAL4815) Pharmacodynamic Target Determination in an In Vivo Murine Model of Invasive Pulmonary Aspergillosis against Wild-Type and cyp51 Mutant Isolates of Aspergillus fumigatus

Alexander J Lepak ¹, Karen Marchillo ¹, Jamie VanHecker ¹, David R Andes ^1,^✉

PMCID: PMC3837846 PMID: 24100500

Abstract

Invasive pulmonary aspergillosis (IPA) continues to rise in concert with increasing numbers of immune suppression techniques to treat other medical conditions and transplantation. Despite these advances, morbidity and mortality rates remain unacceptably high. One strategy used to optimize outcomes is antifungal pharmacodynamic (PD) examination. We explored the pharmacodynamics of a new triazole in development, isavuconazole, in a murine neutropenic IPA model. Ten A. fumigatus isolates were used, including four wild-type isolates and six cyp51 mutants. The MIC range was 0.125 to 8 mg/liter. Following infection, groups of mice were treated orally with the prodrug (BAL8557) at 40 to 640 mg/kg/12 h for 7 days. Efficacy was determined by quantitative PCR of lung homogenates. At the start of therapy, mice had 4.97 log₁₀ conidial equivalents (CE)/ml of lung homogenate, and this increased to 6.82 log₁₀ CE/ml of lung homogenate in untreated animals. The infection model was uniformly lethal in untreated control mice. The PD target endpoints examined included the static-dose AUC/MIC ratio and the 1-log₁₀ killing AUC/MIC ratio. A stasis endpoint was achieved for all isolates with an MIC of ≤1 mg/liter and 1-log₁₀ killing in all isolates with an MIC of ≤0.5 mg/liter, regardless of the presence or absence of the cyp51 mutation. The static-dose range was 65 to 617 mg/kg/12 h. The corresponding median free-drug AUC/MIC ratio was near 5. The 1-log₁₀ killing dose range was 147 to 455 mg/kg/12 h, and the corresponding median free-drug AUC/MIC ratio was 11.1. These values are similar to those previously reported for other triazoles.

INTRODUCTION

Invasive pulmonary aspergillosis (IPA) is a common cause of illness and death in immunocompromised patients (1–7). The development of Aspergillus-active triazoles was a major step forward in therapy; however, morbidity and mortality rates remain unacceptably high. Additionally, the emergence of cyp51 mutant isolates with decreased susceptibility to triazoles is a threat to the efficacy of this drug class (8–13). Therefore, development of novel compounds and examination of the pharmacodynamic (PD) relationships of drug exposure, MIC, and outcome are necessary for the optimal use of these drugs.

PD studies integrate the pharmacokinetic (PK) properties, in vitro potency (MIC), and treatment efficacy of a drug. Common goals of these PD studies are to maximize clinical outcomes through dosing optimization and assist in susceptibility breakpoint determination. These investigations have been integral in the optimal use of antibiotics for bacterial infections and antifungal agents for mucosal and invasive candidiasis (14–18). However, only recently have PD investigations been used for filamentous fungal infections such as IPA (19–23).

Isavuconazonium sulfate (BAL8557) is the water-soluble prodrug of isavuconazole (BAL4815), a novel triazole compound with potent activity against numerous fungal pathogens, including Aspergillus species (24–28). After intravenous or oral administration, the prodrug is rapidly cleaved by plasma esterases to form the active drug isavuconazole (BAL4815) and the inactive cleavage product BAL8728 (25, 29, 30). The drug is currently in clinical development, including two phase III trials examining its efficacy for patients with IPA (http://clinicaltrials.gov, NCT00634049 and NCT00412893). The PD relationships of isavuconazole have been examined in experimental models of invasive candidiasis; however, for IPA, no PD evaluation has been done and targets are unknown. The objectives of the present study were to (i) examine the PD relationship of isavuconazole in a murine model of IPA and (ii) define the optimal isavuconazole exposure for infection due to both wild-type and cyp51 mutant isolates.

MATERIALS AND METHODS

Organisms.

Ten Aspergillus fumigatus isolates were chosen, including nine clinical isolates with and without cyp51 mutations and one laboratory isolate with an Fks1 mutation. Organisms were grown and subcultured on potato dextrose agar (PDA; Difco Laboratories, Detroit, MI). The organisms were chosen on the basis of similar fitness as determined by growth in lungs and mortality rates of untreated animals.

Drug.

Prodrug isavuconazonium sulfate (BAL8557) and isavuconazole (BAL4815) powders were provided by the sponsor (Astellas) for in vivo and in vitro studies, respectively. The prodrug was dissolved in sterile water and buffered to a pH of 4.0 prior to oral administration. Isavuconazole powder was dissolved in dimethyl sulfoxide in accordance with the sponsor's instructions prior to in vitro susceptibility testing. All of the dosages in used this study were administered by the oral route and based upon the oral prodrug dose. All concentration measurements (i.e., PK data and calculated pharmacokinetics) are based upon the active drug. A conversion factor is necessary to compare equivalent prodrug and active-drug amounts on a milligram-per-kilogram basis. This conversion factor was determined on the basis of a prodrug-to-drug equivalency rating of 1.863 (provided by the sponsor) and the 89% purity of the prodrug powder. Thus, the conversion factor for determining the equivalent isavuconazole dose from the prodrug dose was 0.48 (i.e., for every 1 mg/kg of prodrug administered orally, the equivalent in vivo isavuconazole dose would be 0.48 mg/kg). The purity of isavuconazole powder for in vitro susceptibility testing was >99%.

In vitro susceptibility testing.

All isolates were tested by broth microdilution in accordance with CLSI document M38-A2 (31). MICs were determined in duplicate three times. Median values are reported (see Table 1).

Table 1.

In vitro susceptibilities and in vivo fitness of selected A. fumigatus isolates

A. fumigatus isolate	MIC (mg/liter)		In vivo fitness^a	Comment
A. fumigatus isolate	Isavuconazole (BAL4815)	Posaconazole	In vivo fitness^a	Comment
AF41	0.25	0.25	1.85	Wild type
AF293	1	0.5	2.20	Wild type
DPL EC S 1	0.5	0.25	2.63	Wild type
EMFR S678P	0.25	0.25	2.42	Fks1 S678P (echinocandin MIC, >16 mg/liter)
F11628	8	8	2.80	cyp51 G138C
F14403	0.125	8	1.92	cyp51 G54R
F16216	8	2	2.55	cyp51 L98H + TR
AF72	2	2	2.32	cyp51 G54E
F14532	1	1	2.52	cyp51 M220T
F13737	4	2	2.45	cyp51 G434C

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In vivo fitness is defined as the growth, measured in log₁₀ CE/ml of lung homogenate, of the isolate in untreated animals until the time of death or sacrifice.

Animals.

Six-week-old Swiss/ICR specific-pathogen-free female mice weighing 23 to 27 g were used for all experiments (Harlan Sprague-Dawley, Indianapolis, IN). Animals were housed in groups of five and allowed access to food and water ad libitum. Animals were maintained in accordance with the American Association for Accreditation of Laboratory Care criteria (32). Moribund animals showing distress were sacrificed prior to the study endpoint (7 days) in accordance with the recommendations for the humane treatment of laboratory animals. The animal research committee of the William S. Middleton Memorial VA Hospital and the University of Wisconsin—Madison approved the animal studies.

Infection model.

Mice were rendered neutropenic (polymorphonuclear cell counts, <100/mm³) by the subcutaneous (s.c.) injection of 150 mg/kg cyclophosphamide on days −4 and −1. Prior studies have shown that this maintains neutropenia for 4 days; therefore, an additional injection (150 mg/kg) was administered on day +3 to ensure the maintenance of neutropenia throughout the 7-day experiment (20, 33, 34). Additionally, cortisone acetate was administered at 250 mg/kg s.c. on day −1 as previously described (20). Throughout the 7-day experiment, mice were also given ceftazidime at 50 mg/kg/day s.c. to prevent opportunistic bacterial infection. We have previously shown that 100% of the uninfected control animals given the above-described immune suppression and antibiotic prophylaxis survived to the study endpoint, whereas 100% of the infected controls that were left untreated died prior to the study endpoint (20).

Organisms were subcultured on PDA 5 days prior to infection and incubated at 37°C. On the day of infection, the inoculum was prepared by flooding the culture plate with 5 ml of normal saline and 0.05% Tween 20. Gentle agitation was used to release the conidia. The conidial suspension was collected and quantified by hemocytometer (Bright-Line, Hausser Scientific, Horsham, PA). The suspension was diluted to a final concentration of 1.2 × 10⁷ conidia/ml. Viability was confirmed by plating the suspension and performing CFU counts.

An aspiration pneumonia model was used as previously described (20). Briefly, mice were anesthetized with a combination of ketamine and xylazine. Fifty microliters of the suspension of 1 × 10⁷ to 2 × 10⁷ conidia/ml was pipetted into the anterior nares with mice held upright to allow aspiration into the lungs. As previously shown and confirmed in the present study (data not shown), this results in invasive aspergillosis in over 90% of the animals and 100% mortality in untreated infected mice prior to the study endpoint (20). Drug treatment commenced 2 h after the initiation of infection.

Lung processing and organism quantitation.

Lung processing and quantitation of the Aspergillus burdens in the lungs of mice were performed as previously described (35, 36). Briefly, at the time of sacrifice of moribund animals or at the end of therapy (7 days), lungs were aseptically harvested and placed in a 2-oz sterile polyethylene Whirl-Pak bag (Nasco, Fort Atkinson, WI) containing 2 ml of sterile 0.85% NaCl. The lungs were manually homogenized by using direct pressure (37) to produce a primary homogenate. One milliliter of this primary homogenate was then placed in a sterile bead-beating tube (Sarstedt, Newton, NC) with 700 μl of 425- to 600-μm acid-washed glass beads (Sigma-Aldrich, St. Louis, MO). The primary homogenate was bead beaten in a BioSpec BeadBeater (BioSpec, Bartlesville, OK) for 90 s at 4,200 rpm to yield a secondary homogenate. One hundred microliters of this secondary homogenate was mixed with 100 μl Buffer ATL (Qiagen, Valencia, CA) and 20 μl proteinase K (Qiagen, Valencia, CA) and incubated overnight at 56°C with gentle agitation. DNA was then isolated in accordance with the DNeasy Blood and Tissue protocol (Qiagen, Valencia, CA). A final DNA elution step was performed with 100 μl elution buffer (Qiagen, Valencia, CA). The DNA was stored at −20°C until the day of PCR.

Quantitative PCR (qPCR) plates were prepared on the day of assay. Standard quantities of conidia were prepared by hemacytometer counting and used to generate standard curves. The results are reported as conidial equivalents (CE) per milliliter of lung homogenate. Samples were assayed in triplicate with a CFX96 real-time system (Bio-Rad, Hercules, CA). A single-copy gene, Fks1, was chosen for quantitation (38). The primer sequences used included forward primer 5′-GCCTGGTAGTGAAGCTGAGCGT-3′, reverse primer 5′-CGGTGAATGTAGGCATGTTGTCC-3′, and probe 5′–6-carboxyfluorescein–AGCCAGCGGCCCGCAAATG-MGB-3′ (Integrated DNA Technologies, Coralville, IA). The Fks1 mutation (EMFR S678P) was not located in the primer-probe area of the genome. All isolates have been previously studied in an experiment in which known quantities of conidia were used to spike lung homogenate to ensure that the primer-probe set performs similarly for all of the isolates over the dynamic range of interest (10² to 10⁸) (20).

Pharmacokinetics.

The single-dose pharmacokinetics of isavuconazole (BAL4815) were determined in individual ICR/Swiss mice following the administration of the prodrug (BAL8557) at 10, 40, 160, and 640 mg/kg in a 0.2-ml volume by oral-gastric (OG) gavage. Plasma was collected from groups of three isoflurane-anesthetized mice at each of seven time points (0.5, 1, 2, 4, 8, 12, and 24 h). The plasma was stored at −80°C until the day of the drug assay. Drug concentration measurements were performed by the sponsor by liquid chromatography-mass spectrometry as previously described.

A noncompartmental model was used in the PK analysis. PK parameters, including the elimination half-life and the drug concentration at time zero, were calculated via nonlinear least-squares techniques. The area under the concentration-time curve (AUC) was calculated by the trapezoidal rule. For treatment doses in which kinetics were not directly determined, PK parameters were estimated by linear interpolation for those doses between two measured doses and by linear extrapolation for doses above or below the highest and lowest measured doses. Protein binding (99%) was based on previous studies of mice by the sponsor (personal communication).

PD index and magnitude.

The AUC/MIC ratio was used as the PD index for exploration of exposure-response relationships based upon previous PK/PD investigations with triazoles (19–22). Both total- and free (non-protein-bound)-drug concentrations were considered. Neutropenic mice were infected as described above. Treatment consisted of 2-fold increases in the prodrug (BAL8557) concentration (range, 40 to 640 mg/kg) administered every 12 h by OG gavage for 7 days. The doses were selected to vary the effect from maximal to no efficacy and included exposures expected to be achieved with regimens under study in clinical trials. Controls were used for each isolate and included 0-h and untreated controls. Four mice were included in each treatment and control group.

Data analysis.

The qPCR data were modeled according to the Hill-type dose-response equation log₁₀ D = log₁₀ (E/E_max − E)/N + log₁₀ ED₅₀, where D is the drug dose, E is the growth over the study period as measured by qPCR and represented as CE per milliliter of lung homogenate in untreated control mice, E_max is the maximal drug effect, N is the slope of the dose-response curve, and ED₅₀ is the dose needed to achieve a 50% maximal effect. The AUC/MIC ratios of the total- and free-drug concentrations were determined for each isolate. The coefficient of determination (R²) was used to estimate the percent variance in the change in log₁₀ CE per milliliter of lung homogenate over the treatment period for the different dosing regimens that could be attributed to the PD index (AUC/MIC ratio). The dose necessary for net stasis (static dose) and 1-log killing were determined when these endpoints were achieved. Additionally, the PD target total- and free-drug AUC/MIC ratios associated with these endpoints were calculated. The static dose and PD target total- and free-drug AUC/MIC ratios for wild-type and cyp51 mutant isolates were compared by t test for normally distributed data and by Mann-Whitney rank sum test for nonnormally distributed data.

RESULTS

Organism susceptibility and in vivo fitness.

The isavuconazole (BAL4815) susceptibility, genotype, and relative fitness in the in vivo murine model of each isolate are shown in Table 1. The MICs ranged from 0.25 to 1 mg/liter for wild-type isolates and from 0.125 to 8 mg/liter for cyp51 mutants. The organisms exhibited similar in vivo fitness levels on the basis of burden increases in untreated animals until the time of death or sacrifice. At the start of therapy, mice had 4.97 ± 0.33 log₁₀ CE/ml of lung homogenate and the burden increased to 6.82 ± 0.51 log₁₀ CE/ml of lung homogenate in untreated animals. Each isolate produced 100% mortality prior to the study endpoint in untreated animals, with death occurring between days 3 and 6 in all untreated animals.

Pharmacokinetics.

The time courses of isavuconazole (BAL4815) in the plasma of mice following OG doses of 640, 160, 40, and 10 mg/kg of the prodrug (BAL8557) are shown in Fig. 1. Peak levels were achieved within 2 h with each dosing regimen and ranged from 0.51 to 25.4 mg/liter. The elimination half-life in serum increased in a dose-dependent fashion from 1 to 5 h. The AUC from 0 h to infinity (AUC_0-∞), as determined by the trapezoidal rule, ranged from 0.9 to 287 mg · h/liter. The AUC was relatively linear over the dose range (R², 0.98).

Fig 1 — Plasma isavuconazole (BAL4815) concentrations after oral prodrug (BAL8557) administration at 640, 160, 40, and 10 mg/kg. Each symbol represents the geometric mean ± the standard deviation from three mice. The peak concentration (C_max), 24-h AUC_0-∞ (AUC), and elimination half-life (T1/2) are shown for each dose.

Dose-response curves.

A dose-response relationship was observed for each isolate, with higher doses of isavuconazole achieving a larger microbiologic effect (Fig. 2). However, higher doses were necessary to achieve similar microbiologic effects against isolates with elevated isavuconazole MICs. A net static outcome and fungicidal activity were achieved for all wild-type isolates, as well as two of six cyp51 mutants. The maximal effect against wild-type isolates was an approximately 2-log₁₀ reduction in the organism burden compared to that in the lungs at the start of therapy and a nearly 4-log₁₀ reduction compared to untreated controls at the end of therapy.

PD index and target magnitude.

The doses needed to produce net growth suppression (i.e., the static dose) and to produce 1-log₁₀ killing are shown in Table 2. Net stasis was achieved in all isolates that exhibited an MIC of ≤1 mg/liter, whereas 1-log₁₀ killing was observed in all isolates with an MIC of ≤0.5 mg/liter. Therefore, we were able to estimate the static-dose AUC/MIC ratio target for all four wild-type isolates and two of six cyp51 mutants, with the latter two (F14403 and F14532) exhibiting lower MICs than the other four mutant isolates. The static doses for wild-type isolates ranged from 212 to 617 mg/kg/12 h. In comparison, the static doses for the two mutant isolates, F14403 and F14532, were 65 and 515 mg/kg/12 h, respectively. The 1-log₁₀ killing PD target was achieved with three of four wild-type isolates and only a single mutant isolate. The 1-log₁₀ killing doses for wild-type isolates ranged from 302 to 455 mg/kg/12 h, whereas the 1-log₁₀ killing dose was 147 mg/kg/12 h for the single mutant isolate (F14403) with which this endpoint was achieved.

Table 2.

In vivo PD efficacy of isavuconazole in an immunocompromised murine pulmonary aspergillosis model^a

Isolate or parameter	MIC (mg/liter)	Static dose (mg/kg/12 h)	Static-dose 24-h AUC (mg · h/liter	Static-dose 24-h AUC/MIC ratio	Static-dose 24-h free-drug AUC/MIC ratio	1-Log killing dose (mg/kg/12 h)	1-Log killing 24-h AUC (mg · h/liter)	1-Log killing 24-h AUC/MIC ratio	1-Log killing 24-h free-drug AUC/MIC ratio
AF41	0.25	360	278	1,111	11.1	421	311	1,242	12.4
AF293	1	617	415	415	4.15
DPL EC S 1	0.5	393	295	591	5.91	455	328	657	6.57
EMFR S678P	0.25	212	199	794	7.94	302	247	988	9.88
F11628	8
F14403	0.125	65.0	45.9	367	3.67	147	154	1,235	12.4
F16216	8
AF72	2
F14532	1	515	361	361	3.61
F13747	4
Median		376	287	503	5.03	362	279	1,111	11.1
SD		200	131	298	2.98	139	78.7	276	2.76

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Blank cells represent strains for which the endpoint was not achieved.

Total- and free-drug AUC/MIC ratio PD targets are shown in Table 2. The free-drug AUC/MIC ratios associated with net stasis in the wild-type group ranged from 4.15 to 11.1, whereas this endpoint was slightly lower for the two mutant isolates at 3.61 to 3.67. The difference between the two groups was not statistically significant (P = 0.18). For all of the isolates where net stasis was achieved, the median static-dose free-drug AUC/MIC ratio was 5.0. The 1-log₁₀ killing free-drug AUC/MIC ratio was roughly 2-fold higher than the static-dose PD target, with a median value of 11.1. The AUC/MIC ratios and treatment outcome for all organisms were fitted to the Hill sigmoid dose-response model, and the relationship is shown in Fig. 3. The AUC/MIC ratio was a strong predictor of the observed outcome, with an R² value of 0.75.

Fig 3 — Relationship between the PD index total-drug AUC/MIC ratio and the treatment efficacy of isavuconazole against 10 *A. fumigatus* isolates. Open symbols represent wild-type isolates, and closed symbols represent *cyp51* mutants. Each data point represents the geometric mean organism burden of four mice. A best-fit line based on the Hill equation is included.

DISCUSSION

Aspergillus-active triazoles have become the cornerstone of the prevention and treatment of invasive aspergillosis (39). Preclinical animal model PK/PD investigation has proven useful for optimizing therapy for numerous pathogens but has been underused for filamentous fungal pathogens such as Aspergillus. These PD studies are important in the development of novel triazoles, such as isavuconazole, to provide a framework for predicting drug exposures that are expected to achieve a successful therapeutic outcome. Additionally, with the emergence of Aspergillus resistance to the triazole drug class, mediated by mutations in the cyp51 gene, these studies are integral in the examination of susceptibility breakpoints.

PK/PD studies of isavuconazole have been limited to two previous murine disseminated-candidiasis models (40; A. J. Lepak, K. Marchillo, J. VanHecker, and D. R. Andes, submitted for publication). Both showed a very strong relationship between the PD index AUC/MIC ratio and treatment outcome. Results from the present study also demonstrated a strong relationship between the total dose and effect in a murine IPA model. While this is the first PK/PD examination of the triazole isavuconazole for Aspergillus, previous studies using these models with the triazoles voriconazole and posaconazole provide the opportunity to compare results across the class. Employing the same model and diverse group of isolates as in the present study, we have previously shown that a posaconazole free-drug AUC/MIC ratio of approximately 1 was associated with net stasis (20). Similar studies by other investigators using pulmonary and intravascular models found that a posaconazole free-drug AUC/MIC ratio of 1.67 was associated with the ED₅₀, and a value of 3.2 was associated with a 50% increase in survival, respectively (19, 21). A previous study with voriconazole in a murine pulmonary aspergillosis model observed a 50% maximal effect with a free-drug AUC/MIC ratio of 11 (22). The static-dose PD target free-drug AUC/MIC ratio identified in this study for isavuconazole at a median value of 5.0 is congruent with these other in vivo PD triazole studies. For comparison, the ED₅₀, which is shown in Fig. 3, was equivalent to a free-drug AUC/MIC ratio of approximately 7.

In model used in the present study, we used qPCR, which has previously been shown to provide a large dynamic range between effective and ineffective therapy and reproducibility among biological replicates and correlates very well with mortality rates (20). The static dose and 1-log₁₀ dose were the primary PD target endpoints used in this study. It is unclear which PD endpoint in the animal model correlates with the optimal treatment effect in patients. Further clinical PK/PD studies using large sets of patient data, organism susceptibility, and treatment outcomes to delineate the optimal clinical PK/PD target are urgently needed.

In summary, we have shown that the isavuconazole PD index AUC/MIC ratio correlates well with treatment outcome in a murine model of IPA. The MIC was a strong predictor of success or failure regardless of the presence or absence of a cyp51 mutation. Mutations that lead to elevated MICs of other triazoles did not universally correlate with elevated isavuconazole MICs. The median total- and free-drug 24-h AUC/MIC ratio PD targets for net stasis were 503 and 5, respectively. These targets correlate well with other triazole studies using this model. Further clinical study with isavuconazole for IPA is warranted, and it may be a useful addition to the triazole armamentarium for invasive aspergillosis.

ACKNOWLEDGMENTS

Astellas provided funding for the studies described here.

We kindly thank David Perlin for providing isolates DPL EC S 1 and EMFR S678P.

Footnotes

Published ahead of print 7 October 2013

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[B36] 36. Vallor AC, Kirkpatrick WR, Najvar LK, Bocanegra R, Kinney MC, Fothergill AW, Herrera ML, Wickes BL, Graybill JR, Patterson TF. 2008. Assessment of Aspergillus fumigatus burden in pulmonary tissue of guinea pigs by quantitative PCR, galactomannan enzyme immunoassay, and quantitative culture. Antimicrob. Agents Chemother. 52:2593–2598 [DOI] [PMC free article] [PubMed] [Google Scholar]

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[B38] 38. Herrera ML, Vallor AC, Gelfond JA, Patterson TF, Wickes BL. 2009. Strain-dependent variation in 18S ribosomal DNA copy numbers in Aspergillus fumigatus. J. Clin. Microbiol. 47:1325–1332 [DOI] [PMC free article] [PubMed] [Google Scholar]

[B39] 39. Walsh TJ, Anaissie EJ, Denning DW, Herbrecht R, Kontoyiannis DP, Marr KA, Morrison VA, Segal BH, Steinbach WJ, Stevens DA, van Burik JA, Wingard JR, Patterson TF. 2008. Treatment of aspergillosis: clinical practice guidelines of the Infectious Diseases Society of America. Clin. Infect. Dis. 46:327–360 [DOI] [PubMed] [Google Scholar]

[B40] 40. Warn PA, Sharp A, Mosquera J, Spickermann J, Schmitt-Hoffmann A, Heep M, Denning DW. 2006. Comparative in vivo activity of BAL4815, the active component of the prodrug BAL8557, in a neutropenic murine model of disseminated Aspergillus flavus. J. Antimicrob. Chemother. 58:1198–1207 [DOI] [PubMed] [Google Scholar]

PERMALINK

Isavuconazole (BAL4815) Pharmacodynamic Target Determination in an In Vivo Murine Model of Invasive Pulmonary Aspergillosis against Wild-Type and cyp51 Mutant Isolates of Aspergillus fumigatus

Alexander J Lepak

Karen Marchillo

Jamie VanHecker

David R Andes

Abstract

INTRODUCTION