Jamie VanHecker

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

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.

Isavuconazole Pharmacodynamic Target Determination for Candida Species in an In Vivo Murine Disseminated Candidiasis Model

ABSTRACT Pharmacodynamic (PD) studies with triazoles in the neutropenic murine disseminated candidiasis model have been performed extensively for Candida albicans. They have consistently shown that the pharmacodynamic index most closely correlated with efficacy is the ratio of the 24-h area under the concentration-time curve (AUC) to the MIC, and a target 24-h free-drug AUC/MIC ratio near 25 is associated with 50% of maximal microbiologic efficacy. We utilized this model to investigate the pharmacodynamics of isavuconazole. Isavuconazole pharmacokinetics were linear over the dose range studied. Oral-gastric doses of 640, 160, 40, and 10 mg of prodrug/kg of body weight produced peak levels of 0.51 to 25.4 mg/liter, an elimination half-life of 1 to 5 h, and an AUC from 0 h to infinity (AUC0-∞) of 0.9 to 287 mg · h/liter. The AUC/MIC ratio was the pharmacodynamic index that correlated best with efficacy (R2, 0.84). Pharmacodynamic target studies were performed using 4 C. albicans isolates with both a 24-h and a 96-h treatment duration. The strains were chosen to include previously characterized fluconazole-resistant strains. The mean 50% effective doses (ED50) (expressed in mg/kg of body weight/12 h) and associated 24-h free-drug AUC/MIC ratios were 89.3 ± 46.7 and 67.7 ± 35 for the 24-h treatment and 59.6 ± 22 and 33.3 ± 25.5 for the 96-h treatment. These differences were not statistically significant. Pharmacodynamic targets for two non-albicans Candida species were also explored. The mean ED50 (expressed in mg/kg/12 h) and associated 24-h free-drug AUC/MIC ratios were 31.2 and 6.2 for Candida tropicalis (n = 1) and 50.5 and 1.6 for Candida glabrata (n = 2). These PD targets were significantly different from C. albicans targets (P, 0.04). Isavuconazole PD targets for C. albicans are similar to those observed in this model with other triazoles. However, the PD targets for non-albicans Candida species were more than 10-fold lower than those for C. albicans (P, 0.04). This difference is similar to the species-specific PD relationships for the echinocandins. The lower PD targets for these species in this model will be important to consider in the analysis of clinical trial data and during the development of susceptibility breakpoints.

Impact of In Vivo Triazole and Echinocandin Combination Therapy for Invasive Pulmonary Aspergillosis: Enhanced Efficacy against Cyp51 Mutant Isolates

ABSTRACT Previous studies examining combination therapy for invasive pulmonary aspergillosis (IPA) have revealed conflicting results, including antagonism, indifference, and enhanced effects. The most commonly employed combination for this infection includes a mold-active triazole and echinocandin. Few studies have evaluated combination therapy from a pharmacodynamic (PD) perspective, and even fewer have examined combination therapy against both wild-type and azole-resistant Cyp51 mutant isolates. The current studies aim to fill this gap in knowledge. Four Aspergillus fumigatus isolates were utilized, including a wild-type strain, an Fks1 mutant (posaconazole susceptible and caspofungin resistant), and two Cyp51 mutants (posaconazole resistant). A neutropenic murine model of IPA was used for the treatment studies. The dosing design included monotherapy with posaconazole, monotherapy with caspofungin, and combination therapy with both. Efficacy was determined using quantitative PCR, and results were normalized to known quantities of conidia (conidial equivalents [CE]). The static dose, 1-log kill dose, and associated PD target area under the curve (AUC)/MIC ratio were determined for monotherapy and combination therapy. Monotherapy experiments revealed potent activity for posaconazole, with reductions of 3 to 4 log10 Aspergillus CE/ml with the two “low”-MIC isolates. Posaconazole alone was less effective for the two isolates with higher MICs. Caspofungin monotherapy did not produce a significant decrease in fungal burden for any strain. Combination therapy with the two antifungals did not enhance efficacy for the two posaconazole-susceptible isolates. However, the drug combination produced synergistic activity against both posaconazole-resistant isolates. Specifically, the combination resulted in a 1- to 2-log10 decline in burden that would not have been predicted based on the monotherapy results for each drug. This corresponded to a reduction in the free-drug posaconazole AUC/MIC ratio needed for stasis of up to 17-fold. The data suggest that combination therapy using a triazole and an echinocandin may be a beneficial treatment strategy for triazole-resistant isolates.

In Vivo Pharmacodynamic Target Assessment of Eravacycline against Escherichia coli in a Murine Thigh Infection Model

ABSTRACT Eravacycline is a novel fluorocycline antibiotic with potent activity against a broad range of pathogens, including strains with tetracycline and other drug resistance phenotypes. The goal of the studies was to determine which pharmacokinetic/pharmacodynamic (PK/PD) parameter and magnitude best correlated with efficacy in the murine thigh infection model. Six Escherichia coli isolates were utilized for the studies. MICs were determined using CLSI methods and ranged from 0.125 to 0.25 mg/liter. A neutropenic murine thigh infection model was utilized for all treatment studies. Single-dose plasma pharmacokinetics were determined in mice after administration of 2.5, 5, 10, 20, 40, and 80 mg/kg of body weight. Pharmacokinetic studies exhibited maximum plasma concentration (Cmax) values of 0.34 to 2.58 mg/liter, area under the concentration-time curve (AUC) from time zero to infinity (AUC0–∞) values of 2.44 to 57.6 mg · h/liter, and elimination half-lives of 3.9 to 17.6 h. Dose fractionation studies were performed using total drug doses of 6.25 mg/kg to 100 mg/kg fractionated into 6-, 8-, 12-, or 24-h regimens. Nonlinear regression analysis demonstrated that the 24-h free drug AUC/MIC (fAUC/MIC) was the PK/PD parameter that best correlated with efficacy (R2 = 0.80). In subsequent studies, we used the neutropenic murine thigh infection model to determine if the magnitude of the AUC/MIC needed for the efficacy of eravacycline varied among pathogens. Mice were treated with 2-fold increasing doses (range, 3.125 to 50 mg/kg) of eravacycline every 12 h. The mean fAUC/MIC magnitudes associated with the net stasis and the 1-log-kill endpoints were 27.97 ± 8.29 and 32.60 ± 10.85, respectively.

Efficacy of Extended-Interval Dosing of Micafungin Evaluated Using a Pharmacokinetic/Pharmacodynamic Study with Humanized Doses in Mice

ABSTRACT The pharmacokinetic/pharmacodynamic (PK/PD) characteristics of the echinocandins favor infrequent administration of large doses. The in vivo investigation reported here tested the utility of a range of humanized dose levels of micafungin using a variety of prolonged dosing intervals for the prevention and therapy of established disseminated candidiasis. Humanized doses of 600 mg administered every 6 days prevented fungal growth in prophylaxis. Humanized doses of 300 to 1,000 mg administered every 6 days demonstrated efficacy for established infections.

Impact of Glycopeptide Resistance in Staphylococcus aureus on the Dalbavancin In Vivo Pharmacodynamic Target

ABSTRACT Dalbavancin is a novel lipoglycopeptide with activity against Staphylococcus aureus, including glycopeptide-resistant isolates. The in vivo investigation reported here tested the effects of this antibiotic against seven S. aureus isolates with higher MICs, including several vancomycin-intermediate strains. Results of 1-log kill and 2-log kill were achieved against seven and six of the isolates, respectively. The mean free-drug area under the concentration-time curve (fAUC)/MIC values for net stasis, 1-log kill, and 2-log kill were 27.1, 53.3, and 111.1, respectively.

In vivo Pharmacodynamic Evaluation of Omadacycline (PTK 0796) against Streptococcus pneumoniae in the Murine Pneumonia Model

ABSTRACT Omadacycline is a novel aminomethylcycline antibiotic in clinical development for community-acquired bacterial pneumonia (CABP). We used a neutropenic murine pneumonia infection model to characterize the in vivo pharmacodynamic activity of omadacycline against Streptococcus pneumoniae. Four strains with various phenotypic resistances to other antimicrobials, including tetracyclines, were utilized. Drug concentration measurements were performed in the plasma and epithelial lining fluid (ELF) after administration of 0.5, 2, 8, and 32 mg/kg. Pharmacokinetic parameters were calculated using a noncompartmental model and were linear over the dose range. Penetration into ELF ranged from 72 to 102%. Omadacycline demonstrated net cidal activity in relation to the initial burden against all four strains. The pharmacokinetic/pharmacodynamic index AUC/MIC correlated well with efficacy (R2 = 0.74). The plasma 24-h static dose AUC/MIC values were 16 to 20 (24-h ELF AUC/MIC of 14 to 18). A 1-log10 kill was achieved at 24-h plasma AUC/MIC values of 6.1 to 180 (24-h ELF AUC/MIC values 6.0 to 200). A 2-log10 kill was achieved at 24-h plasma AUC/MIC values of 19 to 56 (24-h ELF AUC/MIC of 17 to 47). The targets identified in this study in combination with in vitro potency and favorable human pharmacokinetics make omadacycline an attractive candidate for further development and study in patients with CABP.

In Vivo Pharmacodynamic Evaluation of an FtsZ Inhibitor, TXA-709, and Its Active Metabolite, TXA-707, in a Murine Neutropenic Thigh Infection Model

ABSTRACT Antibiotics with novel mechanisms of action are urgently needed. Processes of cellular division are attractive targets for new drug development. FtsZ, an integral protein involved in cell cytokinesis, is a representative example. In the present study, the pharmacodynamic (PD) activity of an FtsZ inhibitor, TXA-709, and its active metabolite, TXA-707, was evaluated in the neutropenic murine thigh infection model against 5 Staphylococcus aureus isolates, including both methicillin-susceptible and methicillin-resistant isolates. The pharmacokinetics (PK) of the TXA-707 active metabolite were examined after oral administration of the TXA-709 prodrug at 10, 40, and 160 mg/kg of body weight. The half-life ranged from 3.2 to 4.4 h, and the area under the concentration-time curve (AUC) and maximum concentration of drug in serum (Cmax) were relatively linear over the doses studied. All organisms exhibited an MIC of 1 mg/liter. Dose fractionation demonstrated the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC ratio) to be the PD index most closely linked to efficacy (R2 = 0.72). Dose-dependent activity was demonstrated against all 5 isolates, and the methicillin-resistance phenotype did not alter the pharmacokinetic/pharmacodynamic (PK/PD) targets. Net stasis was achieved against all isolates and a 1-log10 kill level against 4 isolates. PD targets included total drug 24-h AUC/MIC values of 122 for net stasis and 243 for 1-log10 killing. TXA-709 and TXA-707 are a promising novel antibacterial class and compound for S. aureus infections. These results should prove useful for design of clinical dosing regimen trials.

In vivo Pharmacodynamic Evaluation of Omadacycline (PTK 0796) against Staphylococcus aureus (SA) in the Murine Thigh Infection Model

Abstract Background Omadacycline is a novel aminomethylcycline antibiotic in development for acute bacterial skin and skin structure infection (ABSSSI) and community acquired bacterial pneumonia (CABP). The goal of the study was to determine the PK/PD targets in the murine thigh infection model against a diverse group of SA pathogens including MRSA. Methods 10 SA strains (4 MSSA, 6 MRSA) were utilized. MICs were determined using CLSI methods. Single dose murine plasma PK was previously determined in our lab and used for PK/PD analyses. The neutropenic murine thigh infection model was utilized for all treatment studies and drug dosing was by subcutaneous route. Four-fold increasing doses of omadacycline (0.25–64 mg/kg) were administered q12h to groups of mice infected with each strain. Treatment outcome was measured by determining organism burden in the thighs (CFU) at the end of each experiment (24 hours). The Emax Hill equation was used to model the dose–response data to the PK/PD index AUC/MIC. The magnitude of the PK/PD index AUC/MIC associated with net stasis and 1-log kill were determined in the thigh model for all strains. Results MICs ranged from 0.25–0.5 mg/L. At the start of therapy, mice had 7.1 ± 0.3 log10 CFU/thigh. In control mice, the organism burden increased 2.3 ± 0.3 log10 CFU/thigh over 24 hours. There was a relatively steep dose–response relationship observed with escalating doses of omadacycline. Maximal organism reductions were 4–5 log10 CFU/thigh compared with untreated controls. Stasis and 1 log-kill (from start of therapy) was observed against each strain. The AUC/MIC magnitude associated with stasis and 1-log kill endpoints are shown in the table. SA Group (n = 10) 24 hours Static Dose (mg/kg) Stasis AUC/
MIC 24 hours 1 log kill Dose (mg/kg) 1 log kill AUC/MIC Mean 13.9 23.7 45.7 78.1 Median 13.0 21.9 39.8 57.7 Std Dev 4.3 10.6 31.4 79.5 Conclusion Omadacycline demonstrated in vivo potency against a diverse group of SA pathogens including MRSA strains. Stasis 24 hours AUC/MIC targets were approximately 24. This is very similar to previous studies of omadacycline against S. pneumoniae (stasis AUC/MIC 18) and other PK/PD evaluations of tetracycline-class antibiotics. 1-log kill targets were only 2–3 fold more than stasis targets for each strain. This data should provide useful in the dose-regimen optimization of omadacycline. Disclosures D. R. Andes, Paratek: Grant Investigator, Research support