Gepotidacin Pharmacokinetics-Pharmacodynamics against Escherichia coli in the One-Compartment and Hollow-Fiber In Vitro Infection Model Systems.

Gepotidacin is a novel, first-in-class triazaacenaphthylene antibiotic that inhibits bacterial DNA replication by a distinct mechanism of action with an in vitro spectrum of activity that includes Escherichia coli. Our objectives herein were the following: (i) to identify the pharmacokinetic-pharmacodynamic (PK-PD) index associated with the efficacy of gepotidacin against E. coli; (ii) to determine the magnitude of the above-described PK-PD index associated with various bacterial reduction endpoints for E. coli; and (iii) to characterize the relationship between gepotidacin exposure and on-therapy E. coli resistance amplification. A 24-h one-compartment in vitro infection model was used to investigate the first two study objectives, and a 10-day hollow-fiber in vitro infection model was used to evaluate the third objective. For the dose-fractionation studies (objective i) in which E. coli NCTC 13441 (gepotidacin MIC, 2 mg/liter) was evaluated, gepotidacin free-drug area under the concentration-time curve (AUC) from 0 to 24 h to the MIC (AUC/MIC ratio) was identified as the PK-PD index most closely associated with change in bacterial burden (r2 = 0.925). For the dose-ranging studies (objective ii), in which four E. coli isolates (gepotidacin MIC range, 1 to 4 mg/liter) were studied, the magnitude of the median gepotidacin free-drug AUC/MIC ratio associated with net bacterial stasis and 1- and 2-log10 CFU reductions for the pooled data set was 33.9, 43.7, and 60.7, respectively. For the hollow-fiber in vitro infection model studies (objective iii), in which one isolate (E. coli NCTC 13441; gepotidacin MIC, 2 mg/liter) was evaluated, gepotidacin free-drug AUC/MIC ratios of 275 and greater were sufficient to suppress on-therapy resistance amplification. Together, the data generated from these studies will be useful to support discrimination among candidate dosing regimens for future clinical study.

Relationship between Gepotidacin Exposure and Prevention of On-Therapy Resistance Amplification in a Neisseria gonorrhoeae Hollow-Fiber In Vitro Infection Model.

Multidrug-resistant Neisseria gonorrhoeae has emerged as a threat to global health. The relationship between gepotidacin exposure and prevention of on-therapy amplification of drug-resistant N. gonorrhoeae was examined using a 7-day hollow-fiber in vitro infection model. The study design included both inactive (no-treatment and ciprofloxacin) and active (ceftriaxone) control regimens. Study drug concentration-time profiles were simulated in the in vitro system for a single oral 0.5 g ciprofloxacin dose, a single intramuscular 0.25 g ceftriaxone dose, and single or two (8 to 12 h apart) oral gepotidacin doses ranging from 0.75 to 12 g. The initial bacterial burden inoculated in the model was 106 CFU/ml. The gepotidacin, ciprofloxacin, and ceftriaxone broth MIC values for the challenge isolate (N. gonorrhoeae GSK #8) were 0.5, 2, and 0.002 mg/liter, respectively. Samples were collected for enumeration of total and drug-resistant bacterial populations and drug concentrations. The no-treatment control reached a bacterial density greater than 108 CFU/ml over 24 h and remained consistent over the 7-day study period. The bacterial density in the model system of the ciprofloxacin regimen matched that of the growth control throughout the study duration, while the ceftriaxone regimen sterilized the model system by the end of day 1. For gepotidacin, a full dose-response relationship was observed. While failure was observed for the 0.75-, 1.5-, and 3-g single-dose regimens, all gepotidacin single- or divided-dose regimens totaling at least 4.5 g prevented resistance amplification and sterilized the model system. These data are useful to provide gepotidacin dose selection support for treating patients with gonorrhea infections.

Pharmacokinetic-Pharmacodynamic Characterization of Omadacycline against Haemophilus influenzae Using a One-Compartment In Vitro Infection Model.

Omadacycline is a novel aminomethylcycline with activity against Gram-positive and -negative organisms, including Haemophilus influenzae, which is one of the leading causes of community-acquired bacterial pneumonia (CABP). The evaluation of antimicrobial agents against H. influenzae using standard murine infection models is challenging due to the low pathogenicity of this species in mice. Therefore, 24-h dose-ranging studies using a one-compartment in vitro infection model were undertaken with the goal of characterizing the magnitude of the ratio of the area under the concentration-time curve (AUC) to the MIC (AUC/MIC ratio) associated with efficacy for a panel of five H. influenzae isolates. These five isolates, for which MIC values were 1 or 2 mg/liter, were exposed to omadacycline total-drug epithelial lining fluid (ELF) concentration-time profiles based on those observed in healthy volunteers following intravenous omadacycline administration. Relationships between change in log10 CFU/ml from baseline at 24 h and the total-drug ELF AUC/MIC ratios for each isolate and for the isolates pooled were evaluated using Hill-type models and nonlinear least-squares regression. As evidenced by the high coefficients of determination (r2) of 0.88 to 0.98, total-drug ELF AUC/MIC ratio described the data well for each isolate and the isolates pooled. The median total-drug ELF AUC/MIC ratios associated with net bacterial stasis and 1- and 2-log10 CFU/ml reductions from baseline at 24 h were 6.91, 8.91, and 11.1, respectively. These data were useful to support the omadacycline dosing regimens selected for the treatment of patients with CABP, as well as susceptibility breakpoints for H. influenzae.

Evaluation of Ceftolozane-Tazobactam in Combination with Meropenem against Pseudomonas aeruginosa Sequence Type 175 in a Hollow-Fiber Infection Model.

The aim of this study was to investigate the efficacy of ceftolozane-tazobactam in combination with meropenem against an extensively drug-resistant (XDR) Pseudomonas aeruginosa high-risk clone, sequence type 175, isolated in a Spanish university hospital. A 14-day hollow-fiber infection model was used to simulate clinical exposure of the two drug regimens alone and in combination, and serial samples were collected to determine drug concentrations and CFU counts. The untreated control failed, as did each study regimen when administered alone. However, when ceftolozane-tazobactam was administered in combination with meropenem, there was a >4-log10 CFU/ml bacterial density reduction and suppression of resistance for the duration of the study. These data suggest that ceftolozane-tazobactam plus meropenem may be a useful combination for treating XDR P. aeruginosa.

Pharmacokinetics-Pharmacodynamics of CB-618 in Combination with Cefepime, Ceftazidime, Ceftolozane, or Meropenem: the Pharmacological Basis for a Stand-Alone ß-Lactamase Inhibitor.

A major challenge in treating patients is the selection of the "right" antibiotic regimen. Given that the optimal ß-lactam/ß-lactamase inhibitor pair is dependent upon the spectrum of ß-lactamase enzymes produced and the frequency of resistance to the ß-lactamase inhibitor, it might be useful if a stand-alone were available for the clinician to pair with the "right" ß-lactam rather than only in a fixed combination. We describe herein a one-compartment in vitro infection model studies conducted to identify the magnitudes of the pharmacokinetic-pharmacodynamic (PK-PD) index for a ß-lactamase inhibitor, CB-618, that would restore the activity of four ß-lactam partner agents (cefepime, ceftazidime, ceftolozane, and meropenem) with various doses (1 or 2 g) and dosing intervals (8 or 12 h). The challenge panel included Klebsiella pneumoniae (n = 5), Escherichia coli (n = 2), and Enterobacter cloacae (n = 1) strains, which produced a wide variety of ß-lactamase enzymes (AmpC, CTXM-15, KPC-2, KPC-3, FOX-5, OXA-1/30, OXA-48, SHV-1, SHV-11, SHV-27, and TEM-1). Free-drug human concentration-time profiles were simulated for each agent, and specimens were collected for drug concentration and bacterial density determinations. CB-618 restored the activity of each ß-lactam partner. The magnitudes of the CB-618 ratio of the area under the concentration-time curve from 0 to 24 h to the MIC (i.e., the AUC/MIC ratio) associated with net bacterial stasis and 1- and 2-log10 CFU/ml reductions from baseline at 24 h were 11.2, 32.9, and 136.3, respectively. These data may provide a PK-PD basis for the development of a stand-alone ß-lactamase inhibitor.

Pharmacokinetics-Pharmacodynamics of Tazobactam in Combination with Cefepime in an In Vitro Infection Model.

We previously demonstrated that for tazobactam administered in combination with ceftolozane, the pharmacokinetic-pharmacodynamic (PK-PD) index that best described tazobactam efficacy was the percentage of the dosing interval that tazobactam concentrations were above a threshold (%T>threshold). Using data from studies of Enterobacteriaceae producing extended-spectrum ß-lactamases (ESBLs), a relationship between tazobactam %T>threshold and reduction in log10 CFU/ml from baseline, for which the tazobactam threshold concentration was the product of the isolate's ceftolozane-tazobactam MIC value and 0.5, was identified. However, since the kinetics of cephalosporin hydrolysis vary among ESBLs and compounds, it is likely that the translational relationship used to derive the tazobactam threshold concentration varies among enzymes and compounds. Using a one-compartment in vitro infection model, the PK-PD of tazobactam administered in combination with cefepime was characterized, and a translational relationship across ESBL-producing Enterobacteriaceae was developed. Four clinical isolates, two Escherichia coli and two Klebsiella pneumoniae isolates, known to produce CTX-M-15 ß-lactamase enzymes and displaying cefepime MIC values of 2 to 4 mg/liter in the presence of 4 mg/liter tazobactam, were evaluated. Tazobactam threshold concentrations from 0.0625× to 1× the tazobactam-potentiated cefepime MIC value were considered. The threshold that best described the relationship between tazobactam %T>threshold and change in log10 CFU/ml from the baseline at 24 h was the product of 0.125 and the cefepime-tazobactam MIC (R2 = 0.813). The magnitudes of %T>threshold associated with net bacterial stasis and a 1-log10 CFU/ml reduction from baseline at 24 h were 21.9% and 52.8%, respectively. These data will be useful in supporting the identification of tazobactam dosing regimens in combination with cefepime for evaluation in future clinical studies.

Bacterial Replication Rate Modulation in Combination with Antimicrobial Therapy: Turning the Microbe against Itself.

A major clinical challenge for treating infectious diseases is the duration of antimicrobial therapy required to eradicate the pathogen. We hypothesized that modulation of the bacterial replication rate in the context of an antimicrobial exposure is coupled with the rate and extent of bactericidal effects. Herein we describe results from in vitro infection model (one compartment, 24-h model; hollow fiber, 10-day model) studies designed to probe the relationship between the bacterial replication rate and the rate and extent of bactericidal effects in the context of an effective antibiotic exposure. The bacterial replication rate was modulated by adjusting the sodium chloride concentration (0 to 8%) in the growth media (Mueller-Hinton II broth). The study drug selected was levofloxacin, and the challenge isolate was Staphylococcus aureus ATCC 29213 (levofloxacin MIC, 0.125 mg/liter). Within each in vitro infection model, human levofloxacin concentration-time profiles (half-life, 7 h) were simulated and the challenge isolate was subjected to an effective exposure (free-drug area under the concentration-time curve over 24 h divided by the MIC [AUC/MIC ratio], 65; administered as a single dose or daily for 10 days). Over the course of each study, samples were taken from each model for bacterial density determinations and drug concentration assay using liquid chromatography-tandem mass spectrometry (LC-MS/MS). In the 24-h one-compartment in vitro infection model studies, as the bacterial replication rate increased, so too did the rate (slope, 0 to 4 h) and extent (24-h CFU count per milliliter) of bacterial killing. In the 10-day hollow-fiber infection model studies, the times until a reduction of bacterial density to 1 × 102 CFU/ml occurred were 10 days in the media in which the challenge isolate grew slowly and approximately 2 days in the media in which the challenge isolate grew rapidly. Together, these data provide a proof of concept for new adjunctive therapeutic options with respect to the use of antimicrobial agents alone that reduce treatment durations. Such adjunctive therapies hold promise for marked reductions in the tonnage of antimicrobial agents administered to patient populations and selection pressure toward antimicrobial resistance.

Pharmacokinetics-Pharmacodynamics of a Novel ß-Lactamase Inhibitor, CB-618, in Combination with Meropenem in an In Vitro Infection Model.

The usefulness of ß-lactam antimicrobial agents is threatened as never before by ß-lactamase-producing bacteria. For this reason, there has been renewed interest in the development of broad-spectrum ß-lactamase inhibitors. Herein we describe the results of dose fractionation and dose-ranging studies carried out using a one-compartment in vitro infection model to determine the exposure measure for CB-618, a novel ß-lactamase inhibitor, most predictive of the efficacy when given in combination with meropenem. The challenge panel included Enterobacteriaceae clinical isolates, which collectively produced a wide range of ß-lactamase enzymes (KPC-2, KPC-3, FOX-5, OXA-48, SHV-11, SHV-27, and TEM-1). Human concentration-time profiles were simulated for each drug, and samples were collected for drug concentration and bacterial density determinations. Using data from dose fractionation studies and a challenge Klebsiella pneumoniae isolate (CB-618-potentiated meropenem MIC = 1 mg/liter), relationships between change from baseline in log10 CFU/ml at 24 h and each of CB-618 area under the concentration-time curve over 24 h (AUC0-24), maximum concentration (Cmax), and percentage of the dosing interval that CB-618 concentrations remained above a given threshold were evaluated in combination with meropenem at 2 g every 8 h (q8h). The exposure measures most closely associated with CB-618 efficacy in combination with meropenem were the CB-618 AUC0-24 (r(2) = 0.835) and Cmax (r(2) = 0.826). Using the CB-618 AUC0-24 indexed to the CB-618-potentiated meropenem MIC value, the relationship between change from baseline in log10 CFU/ml at 24 h and CB-618 AUC0-24/MIC ratio in combination with meropenem was evaluated using the pooled data from five challenge isolates; the CB-618 AUC0-24/MIC ratio associated with net bacterial stasis and the 1- and 2-log10 CFU/ml reductions from baseline at 24 h were 27.3, 86.1, and 444.8, respectively. These data provide a pharmacokinetics-pharmacodynamics (PK-PD) basis for evaluating potential CB-618 dosing regimens in combination with meropenem in future studies.

Dose range evaluation of Mycograb C28Y variant, a human recombinant antibody fragment to heat shock protein 90, in combination with amphotericin B-desoxycholate for treatment of murine systemic candidiasis.

Systemic candidiasis causes significant mortality in patients despite amphotericin B (AMB) therapy. Mycograb C28Y variant, a human recombinant antibody fragment to heat shock protein 90, is closely related to Mycograb, which showed a survival advantage in combination with AMB in a phase III human trial. The Mycograb C28Y variant could potentially increase the antifungal effect of AMB. In our study, the interaction between AMB-desoxycholate (DAMB) and the Mycograb C28Y variant was characterized in vitro by using a checkerboard method. Quantitative cultures of kidneys, livers, and spleens of neutropenic mice with systemic Candida albicans infections were used to assess the in vivo interaction between 1.4 mg/kg of body weight/day of DAMB and 0.15, 1.5, and 15 mg/kg/day of the Mycograb C28Y variant after 1, 3, and 5 days of therapy. DAMB and Mycograb C28Y variant monotherapies, vehicle, and a no-treatment arm served as controls. Also, single- and multidose pharmacokinetics for the Mycograb C28Y variant were determined. Indifference or synergy between DAMB and the Mycograb C28Y variant was seen in two trials by the checkerboard method. The pharmacokinetics of the Mycograb C28Y variant was best described by a 2-compartment model with a median serum t(1/2)(α) of ~0.198 h and a t(1/2)(ß) of ~1.77 h. In mice, DAMB together with the Mycograb C28Y variant was no more effective than AMB alone (P > 0.05 by analysis of variance). The Mycograb C28Y variant alone had no antifungal activity. We therefore conclude that the Mycograb C28Y variant in combination with DAMB offered no benefit over DAMB monotherapy in a neutropenic murine model of systemic candidiasis.