Miao Zhao

In Vivo Pharmacokinetics and Pharmacodynamics of ZTI-01 (Fosfomycin for Injection) in the Neutropenic Murine Thigh Infection Model against Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa

ABSTRACT Fosfomycin is a broad-spectrum agent with activity against Gram-positive and Gram-negative bacteria, including drug-resistant strains, such as extended-spectrum-beta-lactamase (ESBL)-producing and carbapenem-resistant (CR) Gram-negative rods. In the present study, the pharmacokinetic/pharmacodynamic (PK/PD) activity of ZTI-01 (fosfomycin for injection) was evaluated in the neutropenic murine thigh infection model against 5 Escherichia coli, 3 Klebsiella pneumoniae, and 2 Pseudomonas aeruginosa strains, including a subset with ESBL and CR phenotypes. The pharmacokinetics of ZTI-01 were examined in mice after subcutaneous administration of 3.125, 12.5, 50, 200, 400, and 800 mg/kg of body weight. The half-life ranged from 0.51 to 1.1 h, area under the concentration-time curve (AUC0–∞) ranged from 1.4 to 87 mg · h/liter, and maximum concentrations ranged from 0.6 to 42.4 mg/liter. Dose fractionation demonstrated the AUC/MIC ratio to be the PK/PD index most closely linked to efficacy (R2 = 0.70). Net stasis and bactericidal activity were observed against all strains. Net stasis was observed at 24-h AUC/MIC ratio values of 24, 21, and 15 for E. coli, K., pneumoniae and P. aeruginosa, respectively. For the Enterobacteriaceae group, stasis was noted at mean 24-h AUC/MIC ratio targets of 23 and 1-log kill at 83. Survival in mice infected with E. coli 145 was maximal at 24-h AUC/MIC ratio exposures of 9 to 43, which is comparable to the stasis exposures identified in the PK/PD studies. These results should prove useful for the design of clinical dosing regimens for ZTI-01 in the treatment of serious infections due to Enterobacteriaceae and Pseudomonas.

Animal models in the pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents

Animal infection models in the pharmacokinetic/pharmacodynamic (PK/PD) evaluation of antimicrobial therapy serve an important role in preclinical assessments of new antibiotics, dosing optimization for those that are clinically approved, and setting or confirming susceptibility breakpoints. The goal of animal model studies is to mimic the infectious diseases seen in humans to allow for robust PK/PD studies to find the optimal drug exposures that lead to therapeutic success. The PK/PD index and target drug exposures obtained in validated animal infection models are critical components in optimizing dosing regimen design in order to maximize efficacy while minimize the cost and duration of clinical trials. This review outlines the key components in animal infection models which have been used extensively in antibiotic discovery and development including PK/PD analyses.

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.

Comparative Pharmacodynamics of Telavancin and Vancomycin in the Neutropenic Murine Thigh and Lung Infection Models against Staphylococcus aureus

ABSTRACT The pharmacodynamics of telavancin and vancomycin were compared using neutropenic murine thigh and lung infection models. Four Staphylococcus aureus strains were included. The telavancin MIC ranged from 0.06 to 0.25 mg/liter, and the vancomycin MIC ranged from 1 to 4 mg/liter. The plasma pharmacokinetics of escalating doses (1.25, 5, 20, and 80 mg/kg of body weight) of telavancin and vancomycin were linear over the dose range. Epithelial lining fluid (ELF) pharmacokinetics for each drug revealed that penetration into the ELF mirrored the percentage of the free fraction (the fraction not protein bound) in plasma for each drug. Telavancin (0.3125 to 80 mg/kg/6 h) and vancomycin (0.3125 to 1,280 mg/kg/6 h) were administered by the subcutaneous route in treatment studies. Dose-dependent bactericidal activity against all four strains was observed in both models. A sigmoid maximum-effect model was used to determine the area under the concentration-time curve (AUC)/MIC exposure associated with net stasis and 1-log10 kill relative to the burden at the start of therapy. The 24-h plasma free drug AUC (fAUC)/MIC values associated with stasis and 1-log kill were remarkably congruent. Net stasis for telavancin was noted at fAUC/MIC values of 83 and 40.4 in the thigh and lung, respectively, and 1-log kill was noted at fAUC/MIC values of 215 and 76.4, respectively. For vancomycin, the fAUC/MIC values for stasis were 77.9 and 45.3, respectively, and those for 1-log kill were 282 and 113, respectively. The 24-h ELF total drug AUC/MIC targets in the lung model were very similar to the 24-h plasma free drug AUC/MIC targets for each drug. Integration of human pharmacokinetic data for telavancin, the results of the MIC distribution studies, and the pharmacodynamic targets identified in this study suggests that the current dosing regimen of telavancin is optimized to obtain drug exposures sufficient to treat S. aureus infections.

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.

Pharmacodynamic Evaluation of Rezafungin (CD101) against Candida auris in the Neutropenic Mouse Invasive Candidiasis Model

Rezafungin (CD101) is a novel echinocandin under development for once-weekly intravenous (i.v.) dosing. We evaluated the pharmacodynamics (PD) of rezafungin against 4 Candida auris strains, using the neutropenic mouse invasive candidiasis model. ABSTRACT Rezafungin (CD101) is a novel echinocandin under development for once-weekly intravenous (i.v.) dosing. We evaluated the pharmacodynamics (PD) of rezafungin against 4 Candida auris strains, using the neutropenic mouse invasive candidiasis model. The area under the concentration-time curve (AUC)/MIC was a robust predictor of efficacy (R2 = 0.76). The stasis free-drug 24-h AUC/MIC target exposure for the group was 1.88, whereas the 1-log-kill free-drug 24-h AUC/MIC target exposure was 5.77. These values are very similar to those in previous rezafungin PD studies with other Candida spp. Based on recent surveillance susceptibility data, AUC/MIC targets are likely to be exceeded for >90% of C. auris isolates with the previously studied human dose of 400 mg administered i.v. once weekly.

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/u2028MIC 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

Pharmacodynamic Optimization for the Treatment of Invasive Candida auris Infection

Abstract Background Candida auris is an emerging, nosocomial multidrug-resistant threat with high treatment failure rate and mortality. The optimal antifungal agent to use and susceptibility breakpoints are based on limited clinical data. Methods Nine clinical C. auris strains were used. MICs were determined by CLSI standards. Drug treatment studies consisted of: fluconazole (FLC) dose range 0.78–200 mg/kg/12 h, micafungin (MFG) dose range 0.3125–80 mg/kg/24 h, or amphotericin B deoxycholate (AMB) dose range 0.0.78–20 mg/kg/24 hours. Plasma PK was previously determined in the murine model for all three drugs. A 96 h neutropenic murine model of invasive candidiasis (IC) was used for all studies. The Emax Hill equation was used to model the dose–response data to PK/PD index AUC/MIC (FLC and MFG) and Cmax/MIC (AMB). The static and 1 log kill doses (when achieved) and the associated PK/PD targets (AUC/MIC or Cmax/MIC) were determined and compared with previous murine IC studies with C. albicans, C. glabrata, and C. parapsilosis. Results MIC range: FLC 2–256 mg/l, MFG 0.125–4 mg/l, and AMB 0.38–6 mg/l. Dose-dependent activity was observed with all three drugs. Net stasis was achieved against seven strains for FLC, eight strains for MFG, and eight strains for AMB. However, MFG performed significantly better than comparators for cidal endpoints. A 1 log kill endpoint was achieved in eight strains for MFG, whereas this endpoint was only achieved in one strain for FLC and three strains for AMB. PK/PD analyses demonstrated a strong relationship between AUC/MIC and treatment outcome for FLC (R2 0.61) and MFG (R2 0.77); and Cmax/MIC and treatment outcome for AMB (R2 0.64). The median static dose and 1 log kill dose (MFG only) and associated AUC/MIC or Cmax/MIC values are shown (Table). Stasis 1 log kill Drug Dose (mg/kg/24 hours) AUC/MIC or [Cmax/MIC] Dose (mg/kg/24 hours) AUC/MIC FLC 107 26.3 MFG 1.25 53.7 3.36 130 AMB 3.86 [0.87] Conclusion MFG was the most potent drug over the dose range achieving up to 2 log kill against eight of nine strains. PK/PD targets for C. auris against FLC and AMB were similar to other Candida species; however, MFG targets were ≥20-fold lower than C. albicans, C. glabrata, and C. parapsilosis. Using the median stasis targets and human PK for each drug, resistance thresholds could be 16 mg/l for FLC, 2–4 mg/l for MFG, and 1–2 mg/l for AMB. Disclosures All authors: No reported disclosures.

In vivo Pharmacokinetic/Pharmacodynamic (PK/PD) Target Characterization of the Novel, Long Acting Echinocandin CD101 against C. albicans and C. glabrata in the Neutropenic Murine Disseminated Candidiasis Model

Abstract Background CD101 is a novel, long acting echinocandin. The purpose of the study was to evaluate the PK/PD activity of CD101 against C. albicans (CA) and C. glabrata (CG) using the murine neutropenic disseminated candidiasis model. Methods 4 CA and 3 CG strains were used. MICs were determined by CLSI standards. Single dose plasma PK was determined in groups of three mice after IP doses of 1, 4, 16, and 64 mg/kg. For treatment studies, mice were rendered neutropenic via administration of cyclophosphamide at days -4, -1, +2 and +4. Mice were infected with 6.3 ± 0.1 CFU/mL (CA) or 6.2 ± 0.2 CFU/mL (CG) injected into the lateral tail vein. Treatment dose range was 0.016 – 64 mg/kg, given once by IP injection 2 hours after infection. Experiment duration was 7 days at which point kidneys were aseptically harvested for CFU counts. The Emax Hill equation was used to model the dose–response data to PK/PD index AUC/MIC. The static and 1-log kill doses, as well as associated total and free AUC/MIC values were determined for each isolate. Results CD101 MICs were 0.008–0.06 mg/L for CA and 0.06 – 0.5 mg/L for CG. Single dose plasma PK parameter ranges include: Cmax 2.6–77 mg/L, AUC0-∞ 93–4046 mg*hours/L, T1/2 28–41 hours. Dose-dependent cidal activity was observed with a maximal kill of over 2 log10 CFU/kidney. Average 24 hours AUC over 7 days was used to model AUC/MIC data and fit the treatment response data well (CA R2 0.70, CG R2 0.86). The static dose (SD) and 1-log kill dose and associated total and free AUC/MIC values are shown (Table). Strain MIC u2028(mg/L) Static u2028Dose u2028(mg/kg) Stasis Ave 24 hours u2028tAUC/MIC Stasis Ave 24 hours u2028fAUC/MIC 1 log kill dose u2028(mg/kg) 1 log kill Ave u202824 hours tAUC/MIC 1 log u2028kill Ave u202824 hours u2028fAUC/MIC CA K-1 0.008 2.52 3426 44.5 5.26 6435 83.6 580 0.016 1.20 948 12.3 2.03 1429 18.6 98–17 0.06 1.34 274 3.6 2.73 490 6.4 98–210 0.016 1.06 868 11.3 2.28 1574 20.5 CG 10956 0.5 6.29 120 1.6 17.3 301 3.9 5592 0.06 0.03 21.7 0.3 0.51 114 1.5 35315 0.25 0.34 17.9 0.2 2.39 105 1.4 Conclusion CD101 demonstrated in vivo potency in the neutropenic murine disseminated candidiasis model against select CA and CG strains. Similar to studies with other echinocandins, AUC/MIC fit the exposure-response data well and CG targets were numerically lower than CA. However, while CA target range was similar, CG target range was almost 10-fold lower compared with other echinocandins. Disclosures B. Vanscoy, Cidara: Research Contractor, Research support; P. G. Ambrose, Cidara: Research Contractor, Research support; D. R. Andes, Cidara: Grant Investigator, Research support