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Background and Objectives Use of parenteral amikacin to treat refractory nontuberculous mycobacterial (NTM) lung disease is limited by systemic toxicity. A population pharmacokinetic model was developed using data pooled from two randomized trials to evaluate the pharmacokinetic properties of once-daily amikacin liposome inhalation suspension (ALIS) in patients with treatment-refractory NTM lung disease. Methods In phase 2 (TR02-112) and phase 3 (CONVERT) studies, patients with sputum cultures positive for Mycobacterium avium complex (both studies) or M. abscessus (TR02-112) despite ≥ 6 months of guideline-based therapy were treated with once-daily ALIS 590 mg. Results Fifty-three patients (28 Japanese; 25 White) were assessed. At baseline and ≈ 6 months after daily dosing, median maximum concentration (Cmax) was < 2 mg/L and median area under the concentration-time curve (AUC0–24) was

Meropenem-vaborbactam is a broad-spectrum carbapenem-beta-lactamase inhibitor combination approved in the USA and Europe to treat patients with complicated urinary tract infections and in Europe, other serious bacterial infections, including hospital- acquired and ventilator-associated pneumonia. Population pharmacokinetic (PK) models were developed to characterize the time-course of meropenem and vaborbactam using pooled data from two Phase 1 and two Phase 3 studies. Multi-compartment disposition model structures with linear elimination processes were fit to the data using NONMEM 7.2. Since both drugs are cleared primarily by the kidneys, estimated glomerular filtration rate (eGFR) was evaluated as part of the base structural models. For both agents, a two-compartment model with zero-order input and first-order elimination best described the pharmacokinetic PK data and a sigmoidal Hill-type equation best described the relationship between renal clearance and eGFR. For meropenem, the following significant covariate relationships were identified: clearance (CL) decreased with increasing age, CL was systematically different in subjects with end stage renal disease, and all PK parameters increased with increasing weight. For vaborbactam, the following significant covariate relationships were identified: CL increased with increasing height, volume of the central compartment (Vc) increased with increasing body surface area, and CL, Vc, and volume of the peripheral compartment were systematically different in Phase 1 non-infected subjects relative to Phase 3 infected patients, respectively. Visual predictive checks demonstrated minimal bias, supporting the robustness of the final models. These models were useful for generating individual PK exposures for pharmacokinetic-pharmacodynamic (PK-PD) analyses for efficacy and Monte Carlo simulations to evaluate PK-PD target attainment.

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.

It is often said that the marketplace for new antibiotics is broken. This notion is supported by the observation that many recently-approved antibiotics to treat drug-resistant bacteria have failed commercially in a spectacular fashion. Today, companies with peak market-cap values in excess of USD 500 million to 1 billion prior to product launch regularly sell for pennies on the dollar a few years after market introduction. It is possible, however, that the market is not as broken as we perceive. That is, in the collective mind of the clinician, recently-approved antibiotics may be too-poorly differentiated to justify their broad use and inordinate cost relative to those already existing. Perhaps we in the antibacterial drug development field must change our way of thinking if we are to survive and thrive. Rather than reflexively developing new β-lactam-β-lactamase inhibitor combinations for every new enzyme that evades our current inhibitors, we should focus discovery and development efforts on agents that revolutionize how we potentiate antibiotics. To this end, there has been renewed interest in phage therapies, virulence inhibitors, bacterial growth rate modulators, monoclonal antibodies, and other approaches to augment antibiotic effects. Herein, we suggest that the unmet medical need is less about adding poorly-differentiated antibiotics to our armamentarium and more about the need for innovation in how we augment antibiotic regimen effects.

Omadacycline, a novel aminomethylcycline antibiotic with activity against Gram-positive and -negative organisms, including tetracycline-resistant pathogens, received FDA approval in October 2018 for the treatment of patients with acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP). A previously developed population pharmacokinetic (PK) model based on phase 1 intravenous and oral PK data was refined using data from infected patients. Data from 10 phase 1 studies used to develop the previous model were pooled with data from three additional phase 1 studies, a phase 1b uncomplicated urinary tract infection study, one phase 3 CABP study, and two phase 3 ABSSSI studies., Omadacycline, a novel aminomethylcycline antibiotic with activity against Gram-positive and -negative organisms, including tetracycline-resistant pathogens, received FDA approval in October 2018 for the treatment of patients with acute bacterial skin and skin structure infections (ABSSSI) and community-acquired bacterial pneumonia (CABP). A previously developed population pharmacokinetic (PK) model based on phase 1 intravenous and oral PK data was refined using data from infected patients. Data from 10 phase 1 studies used to develop the previous model were pooled with data from three additional phase 1 studies, a phase 1b uncomplicated urinary tract infection study, one phase 3 CABP study, and two phase 3 ABSSSI studies. The final population PK model was a three-compartment model with first-order absorption using transit compartments to account for absorption delay following oral dosing and first-order elimination. Epithelial lining fluid (ELF) concentrations were modeled as a subcompartment of the first peripheral compartment. A food effect on oral bioavailability was included in the model. Sex was the only significant covariate identified, with 15.6% lower clearance for females than males. Goodness-of-fit diagnostics indicated a precise and unbiased fit to the data. The final model, which was robust in its ability to predict plasma and ELF exposures following omadacycline administration, was also able to predict the central tendency and variability in concentration-time profiles using an external phase 3 ABSSSI data set. A population PK model, which described omadacycline PK in healthy subjects and infected patients, was developed and subsequently used to support pharmacokinetic-pharmacodynamic (PK-PD) and PK-PD target attainment assessments.

Background Pharmacokinetic (PK)–pharmacodynamic (PD) indices relate measures of drug exposure to antibacterial effect. Clinical PK–PD studies aim to correlate PK–PD indices with outcomes in patients. Optimization of dosing based on pre-clinical studies means that PK–PD relationships are difficult to establish; therefore studies need to be designed and reported carefully to validate pre-clinical findings. Objectives To describe the methodological features of clinical antibacterial and antifungal PK–PD studies that reported the relationship between PK–PD indices and clinical or microbiological responses. Methods Studies published between 1980 and 2015 were identified through systematic searches. Methodological features of eligible studies were extracted. Results We identified 85 publications containing 97 PK–PD analyses. Most studies were small, with fewer than 100 patients. Around a quarter were performed on patients with infections due to a single specific pathogen. In approximately one-third of studies, patients received concurrent antibiotics/antifungals and in some other studies patients received other treatments that may confound the PK–PD–outcome relationship. Most studies measured antimicrobial concentrations in blood/serum and only four measured free concentrations. Most performed some form of regression, time-to-event analysis or used the Hill/Emax equation to examine the association between PK–PD index and outcome. Target values of PK–PD indices that predict outcomes were investigated in 52% of studies. Target identification was most commonly done using recursive partitioning or logistic regression. Conclusions Given the variability in conduct and reporting, we suggest that an agreed set of standards for the conduct and reporting of studies should be developed.

The current antimicrobial market and old (pre-2000) in vitro antimicrobial susceptibility test interpretative criteria (STIC) are not working properly. Malfunctioning susceptibility breakpoints and antimicrobial markets have serious implications for both patients (ie, from a safety and efficacy perspective) and antibiotic-focused pharmaceutical and biotechnology company economic viability. Poorly functioning STIC fail both patients and clinicians since they do not discriminate between likely effective and ineffective antimicrobial regimens. Poor economic viability fails patients and clinicians as it decreases the industry’s ability to develop antimicrobial agents that clinicians and patients urgently require now and in the future. Herein, we review how STIC for older antimicrobial agents were determined and how their correction can impact the perceived utility of old relative to new antimicrobial agents. Moreover, we describe the data and analysis needs to systematically reevaluate older STIC values. We call for professional infectious diseases societies, government agencies, and other consensus bodies interested in the appropriate use of antimicrobial agents to join an effort to systematically evaluate and, where warranted, correct STIC for all relevant antimicrobial agents. This effort will amplify the effects of other measures designed to increase appropriate antimicrobial use (ie, good antimicrobial stewardship), development, and regulation.

The threat posed by infections arising from antimicrobial-resistant bacteria is a global concern. Despite this trend, the future development of new antimicrobial agents is currently very uncertain. The lack of commercial success for newly launched antimicrobial agents provides little incentive to invest in the development of new agents. To address this crisis, a number of push and pull incentives have been constructed to support antimicrobial drug development. Push incentives, which are designed to lower the cost of developing new antimicrobial agents, include grants, contracts, public-private partnerships, tax credits, and clinical trial networks. Pull incentives, which are designed to facilitate higher financial returns for a newly launched antimicrobial agent, include those that decrease the time for a regulatory review, extend patent exclusivity, or provide premium pricing. Such incentives may also include direct, advanced, or milestone payments or they may be insurance-based whereby healthcare systems pay for the right to access an antimicrobial agent rather than the number of units administered. Another strategy involves the re-evaluation of interpretive criteria for in vitro susceptibility testing (susceptibility breakpoints) of old antimicrobial agents using the same standards applied to that of new agents, which will allow for an accurate determination of antimicrobial resistance. Although each of the above-described strategies will be important to ensure that antimicrobial agents are developed in the decades to come, the update of susceptibility breakpoints for old agents is a strategy that could be implemented quickly and one that could be the most effective for incentivizing drug developers and financiers to reconsider the development of antimicrobial agents., The lack of commercial success for newly launched antimicrobial agents provides little incentive to develop new agents. To address this crisis, several financial incentives have been constructed. Correction of susceptibility breakpoints could be most impactful to incentivizing antimicrobial drug development.

ME1100 (arbekacin inhalation solution) is an inhaled aminoglycoside that is being developed to treat patients with hospital-acquired and ventilator-associated bacterial pneumonia (HABP and VABP, respectively). Pharmacokinetic-pharmacodynamic (PK-PD) target attainment analyses were undertaken to evaluate ME1100 regimens for the treatment of patients with HABP/VABP. The data used included a population pharmacokinetic (PPK) 4-compartment model with 1st-order elimination, nonclinical PK-PD targets from one-compartment in vitro and/or in vivo infection models, and in vitro surveillance data. Using the PPK model, total-drug epithelial lining fluid (ELF) concentration-time profiles were generated for simulated patients with varying creatinine clearance (CLcr) (ml/min/1.73 m(2)) values. Percent probabilities of PK-PD target attainment by MIC were determined based on the ratio of total-drug ELF area under the concentration-time curve (AUC) to MIC (AUC/MIC ratio) targets associated with 1- and 2-log(10) CFU reductions from baseline for Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus. Percent probabilities of PK­PD target attainment based on PK-PD targets for a 1-log(10) CFU reduction from baseline at MIC values above the MIC(90) value for K. pneumoniae (8 μg/ml), P. aeruginosa (4 μg/ml), and S. aureus (0.5 μg/ml) were ≥99.8% for ME1100 600 mg twice daily (BID) in simulated patients with CLcr values >80 to ≤120 ml/min/1.73 m(2). ME1100 600 mg BID, 450 mg BID, and 600 mg once daily in simulated patients with CLcr values >50 to ≤80, >30 to ≤50, and 0 to ≤30 ml/min/1.73 m(2), respectively, provided arbekacin exposures that best matched those for 600 mg BID in simulated patients with normal renal function. These data provide support for ME1100 as a treatment for patients with HABP/VABP.

Use of parenteral amikacin to treat refractory nontuberculous mycobacterial (NTM) lung disease is limited by systemic toxicity. A population pharmacokinetic model was developed using data pooled from two randomized trials to evaluate the pharmacokinetic properties of once-daily amikacin liposome inhalation suspension (ALIS) in patients with treatment-refractory NTM lung disease.In phase 2 (TR02-112) and phase 3 (CONVERT) studies, patients with sputum cultures positive for Mycobacterium avium complex (both studies) or M. abscessus (TR02-112) despite ≥ 6 months of guideline-based therapy were treated with once-daily ALIS 590 mg.Fifty-three patients (28 Japanese; 25 White) were assessed. At baseline and ≈ 6 months after daily dosing, median maximum concentration (CSystemic exposure to amikacin in serum and urine following once-daily ALIS administration in patients with treatment-refractory NTM lung disease was notably lower than that previously reported for parenteral amikacin.ClinicalTrials.gov NCT01315236 (registered March 15, 2011) and NCT02344004 (registered January 22, 2015).

In the current of era of developing antibacterial agents, including those for unmet medical need, Sponsors are required to submit a robust pre-clinical pharmacokinetic-pharmacodynamic (PK-PD) data package in exchange for limited clinical data. However, the clinical data package also needs to be as robust as possible. The clinical data package needs to include the Phase 1 pharmacokinetic (PK) studies conducted in the target patient populations and special populations. Additionally, PK data need to be collected from all patients enrolled in the pivotal trial(s). Such data are critical to confirm adequate drug exposures relative to non-clinical PK-PD targets for efficacy, explain unexpected clinical failures in individuals or groups of patients, and evaluate exposure-response relationships for safety.

The polymyxins are important agents for carbapenem-resistant Gram-negative bacilli. The United States Committee on Antimicrobial Susceptibility Testing breakpoint recommendations for colistin and polymyxin B are that isolates of Pseudomonas aeruginosa , Acinetobacter baumannii , and Enterobacteriaceae are considered susceptible at MIC values of ≤2 mg/liter. These recommendations are contingent upon dosing and testing strategies that are described in this commentary.

Ertapenem provides activity against many pathogens commonly associated with hospital-acquired and ventilator-associated bacterial pneumoniae (HABP and VABP, respectively), including methicillin-susceptible Staphylococcus aureus and numerous Gram-negative pathogens with one major gap in coverage, Pseudomonas aeruginosa. Pharmacokinetic-pharmacodynamic (PK-PD) target attainment analyses were conducted to evaluate ertapenem against the most prevalent Enterobacteriaceae causing HABP/VABP. The objective of these analyses was to provide dose selection support for and demonstrate the appropriateness of ertapenem to empirically treat patients with HABP/VABP when administered with murepavadin, a novel targeted antimicrobial exhibiting a highly specific spectrum of activity against P. aeruginosa. A previously developed population pharmacokinetic model, a total-drug epithelial lining fluid (ELF) to free-drug serum penetration ratio, contemporary in vitro surveillance data for ertapenem against Enterobacteriaceae, and percentage of the dosing interval for which drug concentrations exceed the MIC value (%T>MIC) targets associated with efficacy were used to conduct Monte Carlo simulations for five ertapenem regimens administered over short or prolonged durations of infusion. Overall total-drug ELF percent probabilities of PK-PD target attainment based on a %T>MIC target of 35% among simulated patients with HABP/VABP arising from Enterobacteriaceae based on pathogen prevalence data for nosocomial pneumonia ranged from 89.1 to 92.7% for all five ertapenem regimens evaluated. Total-drug ELF percent probabilities of PK-PD target attainment ranged from 99.8 to 100%, 97.9 to 100%, 10.6 to 74.1%, and 0 to 1.50% at MIC values of 0.06, 0.12, 1, and 4 μg/ml, respectively (MIC(90) values for Escherichia coli, Serratia marcescens, Enterobacter species, and Klebsiella pneumoniae, respectively). Results of these analyses provide support for the evaluation of ertapenem in combination with murepavadin for the treatment of patients with HABP/VABP.

Objectives Lefamulin is a semi-synthetic intravenous (iv) and oral pleuromutilin antibiotic active against community-acquired bacterial pneumonia (CABP) pathogens. Pharmacokinetic/pharmacodynamic (PK/PD) target attainment analyses were carried out to evaluate lefamulin 150 mg iv q12h and 600 mg orally q12h under fed and fasted conditions for the treatment of patients with CABP. Methods The analyses undertaken used a population PK model based on Phase 1 PK data, non-clinical PK/PD targets for efficacy and in vitro surveillance data for Streptococcus pneumoniae (SP) and Staphylococcus aureus (SA), and Monte Carlo simulation. Percentage probabilities of PK/PD target attainment by MIC on day 1 were determined using median total-drug epithelial lining fluid (ELF) and free-drug plasma AUC:MIC ratio targets associated with 1 and 2 log10 cfu reductions from baseline. Results Percentage probabilities of attaining the total-drug ELF AUC:MIC ratio target for a 1 log10 cfu reduction from baseline for SP were ≥99.2% at the MIC90 of 0.12 mg/L and 96.7%, 82.1% and 96.3% for iv and oral dosing regimens under fed and fasted conditions, respectively, at the MIC99 of 0.25 mg/L. Percentage probabilities of attaining the free-drug plasma AUC:MIC target for the same endpoint at the SP MIC99 were 100% for each regimen. For the SA MIC90 of 0.12 mg/L and AUC:MIC ratio targets for the same endpoint, percentage probabilities were 92.7%–100% for iv and oral dosing regimens. Conclusions These data provide support for lefamulin 150 mg iv q12h and 600 mg orally q12h for the treatment of patients with CABP and suggest that doses may not need to be taken under fasted conditions.

ME1100, an inhalation solution of arbekacin, an aminoglycoside, is being developed for the treatment of hospital-acquired and ventilator-associated bacterial pneumonia. The objective of these analyses was to develop a population pharmacokinetic model to describe the arbekacin concentration-time profile in plasma and epithelial lining fluid (ELF) following ME1100 administration. Data were obtained from a postmarketing study for an intravenous (i.v.) formulation of arbekacin, a phase 1 study of ME1100 in healthy volunteers, and a phase 1b study of ME1100 in mechanically ventilated subjects with bacterial pneumonia. Data from the postmarketing study were utilized to develop a population pharmacokinetic model following i.v. administration, and this model was subsequently utilized as the foundation for development of the model characterizing arbekacin disposition following inhalation of ME1100. The final model utilized two compartments for both plasma and ELF disposition, with movement of arbekacin between the ELF and plasma parameterized using linear first-order rate constants. A bioavailability term was included for the inhalational route of administration, which was estimated to be 19.5% for a typical subject. The model included normalized creatinine clearance (CLcrn) and weight as covariates on arbekacin clearance: CL = (weight/52.2)0.855·[(CLcrn–77)·0.0289 + 2.32]. The model simultaneously described arbekacin concentrations following both i.v. and inhaled administration and provided acceptable fits to the plasma and ELF data (r2 of 0.922 and 0.557 for observed versus fitted concentrations, respectively). The developed model will be useful for conducting future analyses to support ME1100 dose selection.

Solithromycin (CEM-101) is a novel fluoroketolide antimicrobial agent with activity against typical and atypical pathogens associated with community-acquired bacterial pneumonia. Using a neutropenic murine lung infection model, the objectives of this study were to identify the pharmacokinetic/pharmacodynamic (PK/PD) index most closely associated with efficacy and the magnitude of such indices associated with solithromycin efficacy against Streptococcus pneumoniae. Plasma and epithelial lining fluid (ELF) samples for pharmacokinetics (PK) were collected serially over 24 hours from healthy mice administered single doses of solithromycin (0.625 to 40 mg/kg). Neutropenic CD-1 mice infected with 10(8) CFUs of one of five S. pneumoniae isolates were administered solithromycin (0.156 to 160 mg/kg/day) via oral gavage. Doses were administered in a fractionated manner for mice infected with one isolate, while mice infected with the remaining four isolates received solithromycin as either a regimen every 6 hours or every 12 hours. A three-compartment model best described solithromycin PK in the plasma and ELF (r(2) = 0.935 and 0.831, respectively). The ratio of total-drug ELF to free-drug plasma area under the concentration-time curve (AUC) from time 0 to 24 hours was 2.7. Free-drug plasma and total-drug ELF AUC to minimum inhibitory concentration ratios (AUC/MIC ratios) were most predictive of efficacy (r(2) = 0.851 and 0.850, respectively). The magnitude of free-drug plasma/total-drug ELF AUC/MIC ratios associated with net bacterial stasis and a 1- and 2-log(10) CFU reduction from baseline was 1.65/1.26, 6.31/15.1, and 12.8/59.8, respectively. These data provided dose selection support for solithromycin for clinical trials in patients with community-acquired bacterial pneumonia.

Background Tebipenem pivoxil hydrobromide (tebipenem HBr), an orally (PO) bioavailable prodrug of tebipenem, is a carbapenem with broad-spectrum activity against Gram-positive and -negative bacteria that is being developed for the treatment of patients with complicated urinary tract infections, including AP. Data from a one-compartment in vitro infection model demonstrated that the ratio of free-drug plasma area under the curve (AUC) to MIC with adjustment for dosing interval (τ) (AUC:MIC ratio•1/τ) was the PK-PD index most associated with tebipenem HBr efficacy [VanScoy BD et al., IDWeek 2019, Poster 1565]. Studies were undertaken to characterize the magnitude of tebipenem HBr free-drug plasma AUC:MIC ratio•1/τ associated with efficacy for Enterobacteriaceae using a neutropenic murine AP model. Methods A single dose pharmacokinetic study was completed in neutropenic mice infected via intra-renal injection with 104 CFU/kidney of Escherichia coli NCTC 13441. Following PO administration of 4 tebipenem HBr doses (1, 15, 45 and 100 mg/kg), plasma samples were collected at 0.25, 0.5, 1, 2, 4, 6 and 8 hours post-treatment initiation and drug concentrations were determined using LC/MS/MS. Dose-ranging studies were completed using a panel of 7 Enterobacteriaceae isolates (tebipenem HBr MIC values of 0.015 to 0.5 mg/L). Mice were infected with 104 CFU/kidney via intra-renal injection. Two hours post-incubation, 8 total daily tebipenem HBr doses (0.3 to 135 mg/kg) were fractionated into regimens given every 8 hours. The relationship between change in log10 CFU/g from baseline at 24 hours and free-drug plasma AUC:MIC ratio•1/τ was fit using a Hill-type model. Free-drug plasma AUC:MIC ratio•1/τ values associated with net bacterial stasis and 1- and 2-log10 CFU/g reductions from baseline at 24 hours were determined. Results The relationship between change in log10 CFU/g from baseline at 24 hours and tebipenem HBr free-drug plasma AUC:MIC ratio•1/τ described the data well (r2 = 0.833). Free-drug plasma AUC:MIC ratio•1/τ values associated with net bacterial stasis and a 1-log10 CFU/g reduction from baseline were 26.2 and 54.1, respectively. A 2-log10 CFU/g reduction was not achieved. Relationship between change in log10 CFU/g from baseline at 24 hours and tebipenem HBr free-drug plasma AUC:MIC ratio•1/τ based on data for a panel of Enterobacteriaceae isolates evaluated in the dose-ranging studies conducted using a neutropenic murine acute pyelonephritis model Conclusion These data will be useful to support tebipenem HBr dose selection for clinical studies in patients with AP. Disclosures Brian D. VanScoy, B.S., Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Steven Fikes, BA, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Christopher M. Rubino, PharMD, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Sujata M. Bhavnani, PharMD, MS, FIDSA, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support) Nicole S. Cotroneo, BS, Spero Therapeutics (Employee, Shareholder) Ian A. Critchley, PhD, Spero Therapeutics (Employee, Shareholder) Thomas R. Parr, PhD, Spero Therapeutics (Employee, Shareholder) Paul G. Ambrose, PharMD, FIDSA, Institute for Clinical Pharmacodynamics, Inc. (Employee)Spero Therapeutics (Grant/Research Support)

Background Gatifloxacin is used for the treatment of multidrug-resistant tuberculosis (MDR-TB). The optimal dose is unknown. Methods We performed a 28-day gatifloxacin hollow-fiber system model of tuberculosis (HFS-TB) study in order to identify the target exposures associated with optimal kill rates and resistance suppression. Monte Carlo experiments (MCE) were used to identify the dose that would achieve the target exposure in 10000 adult patients with meningeal or pulmonary MDR-TB. The optimal doses identified were validated using probit analyses of clinical data from 2 prospective clinical trials of patients with pulmonary and meningeal tuberculosis. Classification and regression-tree (CART) analyses were used to identify the gatifloxacin minimum inhibitory concentration (MIC) below which patients failed or relapsed on combination therapy. Results The target exposure associated with optimal microbial kill rates and resistance suppression in the HFS-TB was a 0–24 hour area under the concentration-time curve-to-MIC of 184. MCE identified an optimal gatifloxacin dose of 800 mg/day for pulmonary and 1200 mg/day for meningeal MDR-TB, and a clinical susceptibility breakpoint of MIC ≤ 0.5 mg/L. In clinical trials, CART identified that 79% patients failed therapy if MIC was >2 mg/L, but 98% were cured if MIC was ≤0.5 mg/L. Probit analysis of clinical data demonstrated a >90% probability of a cure in patients if treated with 800 mg/day for pulmonary tuberculosis and 1200 mg/day for meningeal tuberculosis. Doses ≤400 mg/day were suboptimal. Conclusions Gatifloxacin doses of 800 mg/day and 1200 mg/day are recommended for pulmonary and meningeal MDR-TB treatment, respectively. Gatifloxacin has a susceptible dose-dependent zone at MICs 0.5–2 mg/L.

Background Levofloxacin is used for the treatment of multidrug-resistant tuberculosis; however the optimal dose is unknown. Methods We used the hollow fiber system model of tuberculosis (HFS-TB) to identify 0–24 hour area under the concentration-time curve (AUC0-24) to minimum inhibitory concentration (MIC) ratios associated with maximal microbial kill and suppression of acquired drug resistance (ADR) of Mycobacterium tuberculosis (Mtb). Levofloxacin-resistant isolates underwent whole-genome sequencing. Ten thousands patient Monte Carlo experiments (MCEs) were used to identify doses best able to achieve the HFS-TB–derived target exposures in cavitary tuberculosis and tuberculous meningitis. Next, we used an ensemble of artificial intelligence (AI) algorithms to identify the most important predictors of sputum conversion, ADR, and death in Tanzanian patients with pulmonary multidrug-resistant tuberculosis treated with a levofloxacin-containing regimen. We also performed probit regression to identify optimal levofloxacin doses in Vietnamese tuberculous meningitis patients. Results In the HFS-TB, the AUC0-24/MIC associated with maximal Mtb kill was 146, while that associated with suppression of resistance was 360. The most common gyrA mutations in resistant Mtb were Asp94Gly, Asp94Asn, and Asp94Tyr. The minimum dose to achieve target exposures in MCEs was 1500 mg/day. AI algorithms identified an AUC0-24/MIC of 160 as predictive of microbiologic cure, followed by levofloxacin 2-hour peak concentration and body weight. Probit regression identified an optimal dose of 25 mg/kg as associated with >90% favorable response in adults with pulmonary tuberculosis. Conclusions The levofloxacin dose of 25 mg/kg or 1500 mg/day was adequate for replacement of high-dose moxifloxacin in treatment of multidrug-resistant tuberculosis.

Despite a number of studies reporting that ertapenem pharmacokinetic parameters differ considerably in obese patients from those in healthy volunteers, functions describing the relationships between this agent's pharmacokinetics and indicators of body size have not been developed. The aim of this analysis was to develop an ertapenem population pharmacokinetic model using data from a previously described study in normal-weight, obese, and morbidly obese healthy volunteers. A single ertapenem 1-g dose administered intravenously was evaluated in 30 subjects within different body mass index (BMI) categories. The population pharmacokinetic model was developed using the first-order conditional estimation method with interaction (FOCE-I) algorithm within NONMEM. The ability of age, sex, renal function, and various body size measures (total body weight, height, body mass index, ideal body weight, fat-free mass, and body surface area [BSA]) to explain a portion of the interindividual variability on select pharmacokinetic parameters was explored using stepwise forward selection (α = 0.01) and backward elimination (α = 0.001). The data were best described using a linear three-compartment model with total body weight as a covariate on clearance (CL = 1.79 · [weight/95.90](0.278)) and BSA as a covariate on central volume (Vc = 4.76 · [BSA/2.06](1.86)). After accounting for fixed effects, the estimated interindividual variability was very low (

Rezafungin (CD101) is a novel echinocandin antifungal agent with activity against Aspergillus and Candida species, including azole- and echinocandin-resistant isolates. The objective of these analyses was to conduct pharmacokinetic (PK)-pharmacodynamic (PD) target attainment analyses to evaluate single and once-weekly rezafungin dosing to provide dose selection support for future clinical studies. Using a previously developed rezafungin population PK model, Monte Carlo simulations were conducted utilizing the following three intravenous rezafungin regimens: (i) a single 400 mg dose, (ii) 400 mg for week 1 followed by 200 mg weekly for 5 weeks, and (iii) 400 mg weekly for 6 weeks. Percent probabilities of achieving the nonclinical PK-PD targets associated with net fungal stasis and 1-log 10 CFU reductions from baseline for Candida albicans and Candida glabrata were calculated for each rezafungin regimen. At the MIC 90 for C. albicans and C. glabrata , a single 400 mg dose of rezafungin achieved probabilities of PK-PD target attainment of ≥90% through week 3 of therapy for all PK-PD targets evaluated. When evaluating the multiple-dose (i.e., weekly) regimens under these conditions, percent probabilities of PK-PD target attainment of 100% were achieved through week 6. Moreover, high (>90%) probabilities of PK-PD target attainment were achieved through week 6 following administration of the weekly regimens at or above the MIC 100 values for C. albicans and C. glabrata based on contemporary in vitro surveillance data. These analyses support the use of single and once-weekly rezafungin regimens for the treatment of patients with candidemia and/or candidiasis due to C. albicans or C. glabrata .

Ventilator-associated bacterial pneumonia (VABP) is a difficult therapeutic problem. Considerable controversy exists regarding the optimal chemotherapy for this entity. The recent guidelines of the Infectious Diseases Society of America and the American Thoracic Society recommend a 7-day therapeutic course for VABP based on the balance of no negative impact on all-cause mortality, less resistance emergence, and fewer antibiotic treatment days, counterbalanced with a higher relapse rate for patients whose pathogen is a nonfermenter. The bacterial burden causing an infection has a substantial impact on treatment outcome and resistance selection. We describe the baseline bronchoalveolar lavage (BAL) fluid burden of organisms in suspected VABP patients screened for inclusion in a clinical trial. We measured the urea concentrations in plasma and BAL fluid to provide an index of the dilution of the bacterial and drug concentrations in the lung epithelial lining fluid introduced by the BAL procedure. We were then able to calculate the true bacterial burden as the diluted colony count times the dilution factor. The median dilution factor was 28.7, with the interquartile range (IQR) being 11.9 to 53.2. Median dilution factor-corrected colony counts were 6.18 log

Meropenem-vaborbactam is a fixed combination of the novel β-lactamase inhibitor vaborbactam and the carbapenem antibiotic meropenem, developed for the treatment of serious infections caused by drug-resistant Gram-negative bacteria. The safety, tolerability, and pharmacokinetics (PK) of vaborbactam and meropenem following single and multiple ascending doses of each study drug administered alone or combined were evaluated in 76 healthy adult subjects in a randomized, placebo-controlled, double-blind study. Subjects were enrolled in 1 of 5 dose cohorts (receiving 250 to 2,000 mg vaborbactam and/or 1,000 to 2,000 mg meropenem) alone or in combination. No subjects discontinued the study due to adverse events (AEs), and no serious AEs were observed. The pharmacokinetics of meropenem and vaborbactam were similar when given alone or in combination; all evaluated plasma PK exposure measures (peak plasma concentration, area under the plasma concentration-time curve [AUC] from time zero to the last measurable concentration area under the plasma concentration-time curve, and AUC from time zero to infinity) were similar for the study drugs alone versus those in combination, indicating no pharmacokinetic interaction between meropenem and vaborbactam. Across all treatments, 47 to 64% of an administered meropenem dose and 75 to 95% of vaborbactam was excreted unchanged in the urine over 48 h postdose. Meropenem and vaborbactam, when given alone or in combination, have similar pharmacokinetic properties, with no plasma or urine PK drug-drug interactions, and are well tolerated. These findings supported further clinical investigation of the combination product. (This study is registered at ClinicalTrials.gov under registration no. NCT01897779.)

The original version of this article contained incorrect Supplementary Files. The correct Supplementary Files are published with this erratum.

First-line antifungal therapies are limited to azoles, polyenes and echinocandins, the former two of which are associated with high occurrences of severe treatment-emergent adverse events or frequent drug interactions. Among antifungals, echinocandins present a unique value proposition given their lower rates of toxic events as compared with azoles and polyenes. However, with the emergence of echinocandin-resistant Candida species and the fact that a pharmacometric approach to the development of anti-infective agents was not a mainstream practice at the time these agents were developed, we question whether echinocandins are being dosed optimally. This review presents pharmacokinetic/pharmacodynamic (PK/PD) evaluations for approved echinocandins (anidulafungin, caspofungin and micafungin) and rezafungin (previously CD101), an investigational agent. PK/PD-optimized regimens were evaluated to extend the utility of approved echinocandins when treating patients with resistant isolates. Although the benefits of these regimens were apparent, it was also clear that anidulafungin and micafungin, regardless of dosing adjustments, are unlikely to provide therapeutic exposures sufficient to treat highly resistant isolates. Day 1 probabilities of PK/PD target attainment of 5.2% and 85.1%, respectively, were achieved at the C. glabrata MIC90 (0.12 mg/L) and MIC97 (0.06 mg/L) values, respectively, for these agents. However, evaluations of rezafungin demonstrated high probabilities of target attainment over 4 weeks of therapy (100%) after administration of a single-dose regimen at the MIC90 of 0.06 mg/L. This signals that although existing therapies are not optimal to treat resistant organisms, more potent new echinocandins (relative to achievable drug exposures) may be on the horizon.

Background SPR859 (tebipenem) is the active form of the orally bioavailable prodrug SPR994. Tebipenem is an oral carbapenem with a broad-spectrum activity against Gram-positive and -negative bacteria. SPR994 is being developed as an oral option for the treatment of complicated urinary tract infections (cUTI). The goal of these studies was to characterize the PK-PD of tebipenem against a diverse panel of Enterobacteriaceae. Methods 24-hour dose-fractionation and dose-ranging studies were carried out utilizing the one-compartment in vitro infection model. Bacteria (1 × 106 CFU/mL) were exposed to tebipenem concentrations that mimicked human healthy volunteer free-drug plasma (f) concentration–time profiles following oral drug administration. For the dose-fractionation studies, 7 total daily dose levels (fAUC range, 0.11 to 19.0 mg hours/L) were fractionated in equal divided doses administered every 4, 8 or 12 hours (q4h, q8h and q12h, respectively). A single challenge isolate, E. coli ATCC 25922 (MIC = 0.015 mg/L), was evaluated in the dose-fractionation studies. In the dose-ranging studies, 13 Enterobacteriaceae clinical isolates (MIC values from 0.008 to 0.25 mg/L) were exposed to doses ranging from 4.69 to 1200 mg administered q8h (fAUC ranging from 0.14 to 37.2 mg hours/L). Relationships between change in log10 CFU from baseline at 24 h and each of fCmax:MIC ratio, f%T>MIC, and fAUC:MIC ratio, with and without adjustment for dosing interval tau for the latter (fAUC:MIC ratio·1/τ), were fit using Hill-type models. Results Dose-fractionation study results demonstrated the activity of tebipenem to be time-dependent, with both f%T>MIC and fAUC:MIC ratio·1/τ similarly describing the PK-PD of tebipenem. The relationship between change in log10 CFU from baseline at 24 hours and fAUC:MIC ratio·1/τ, as assessed using pooled data for 13 Enterobacteriaceae isolates evaluated in the dose-ranging studies, described the PK-PD of tebipenem well (Figure 1). The magnitude of fAUC:MIC ratio·1/τ associated with net bacterial stasis and 1- and 2-log10 CFU reductions from baseline was 7.23, 13.1, and 32.4, respectively. Conclusion These data will be useful to design other pre-clinical studies and support tebipenem dose selection for clinical studies in patients with cUTI. Disclosures All authors: No reported disclosures.

Background OMC, an aminomethylcycline structurally related to tetracycline agents, was recently approved by the US FDA for the treatment of adult patients with ABSSSI (IV-to-PO and PO regimens) and CABP (IV-to-PO regimen). To better understand exposure-related concerns for ALT increase, PK-PD relationships for ALT were evaluated using data from OMC-treated patients enrolled in three Phase 3 studies. Methods Repeated-measures multiple linear regression was used to evaluate factors predictive of ALT, including different OMC total-drug AUC measures prior to each ALT, with interactions and covariates selected stepwise. Using a final AIC-optimized model, predicted percent probabilities of ALT elevation >1, 1.5, 2, 3, 5, and 10 × upper limit of normal (ULN) at any time post-baseline and up to 2 days after the end of therapy were calculated among analysis patients for fixed post-baseline OMC AUC measures, and among simulated patients after IV-to-PO and PO dosing regimens. Results The final model, developed using data from 327 patients with PK, included increased prior cumulative AUC among males, increased baseline gamma-glutamyl transferase, and study (ABSSSI, PO only) as factors predictive of increased ALT (P < 0.0001). However, the model-predicted impact of OMC across fixed average daily AUC values on ALT elevation endpoints of >1, 1.5, 2, 3, 5, and 10 × ULN was minimal (Figure 1), even for males despite the interaction with AUC (Figure 2). Among all patients, the estimated increases in percent probabilities for the 90th percentile of AUC relative to zero AUC were 5.81, 5.20, 1.53, 0.61, 0.31, and 0%, respectively, and ≤11.5, 7.76, 8.33, 1.31, 1.31, and 0%, respectively, across single variable patient subsets. Percent probabilities of ALT elevation endpoints were within 2.84% when comparing simulated and observed patients after administration of OMC IV-to-PO and PO dosing regimens (Figure 3). Conclusion A statistically significant relationship between an increase in ALT and increase in OMC AUC for males in the presence of other factors was found. However, increases in model-predicted ALT elevation endpoints across fixed OMC AUC values, or among simulated patients after administration of OMC IV-to-PO and PO dosing regimens relative to observed patients, were minimal. Disclosures All authors: No reported disclosures.

Background Omadacycline is a novel aminomethylcycline with activity against Gram-positive and -negative organisms, including tetracycline-resistant pathogens. Omadacycline was recently approved in the United States for treatment of adult patients with community-acquired bacterial pneumonia (CABP) and acute bacterial skin and skin structure infections. Analyses were undertaken to determine whether PORT risk class and CURB-65 score influence the pharmacokinetics of omadacycline in patients with CABP. Methods Omadacycline pharmacokinetic data were available from omadacycline-treated patients with CABP enrolled in the Phase 3 OPTIC Study. Patients received omadacycline 100 mg IV q12h on Day 1 followed by 100 mg IV q24h. After Day 3, patients could be switched to 300 mg PO q24h if predefined clinical stability criteria were met. Four pharmacokinetic samples per patient were collected between Days 2 and 5. These data were previously utilized in the development of a population pharmacokinetic model describing the disposition of omadacycline [Microbe 2018; Abstr SAT-628]. Individual post-hoc parameter estimates for patients enrolled in the OPTIC study were utilized to compute Day 1 total-drug plasma area under the concentration-time curve (AUC) values following administration of omadacycline 100 mg IV q12h. Differences among these AUC values by PORT risk class and CURB-65 score were assessed using a one-way ANOVA. Results A total of 187 pharmacokinetic samples were available from 50 patients. Among the patients classified as PORT risk class II, III, and IV (n = 12, 28, and 10, respectively), mean Day 1 omadacycline AUC values were 10.2, 11.0, and 12.0 mg L/h, respectively. Among patients with CURB-65 scores of 0, 1, and 2 (n = 23, 23, and 4, respectively), mean Day 1 omadacycline AUC values were 10.6, 11.6, and 9.7 mg L/h, respectively. The differences in mean AUC values were not statistically significant among patients by PORT risk class (P = 0.248) and CURB-65 score groups (P = 0.745). Moreover, variability was similar across these groups as displayed in Figure 1. Conclusion Omadacycline exposures were similar across PORT risk class and CURB-65 score groups; thus, omadacycline dose adjustments based on these classifications are likely not warranted. Disclosures All authors: No reported disclosures.

Background In 2015 USCAST, the National Advisory Committee for the United States (US) to EUCAST, produced a report (Version 1.0) on their website (www.uscast.org) re-evaluating fluoroquinolone (FQ) breakpoint interpretive criteria (IC) based on analysis of current microbiology and pharmacokinetic/pharmacodynamic (PK/PD) data. EUCAST initiated a consultative process using USCAST analyses in an effort to update FQ IC, released in 2017. CLSI formed an ad-hoc working group in late 2015 to review the USCAST FQ document and formulate questions about content. In 2018, USCAST released V1.3 of the FQ document and CLSI subsequently published updated FQ MIC IC in the M100-S29 (2019) document. This study evaluated the impact on susceptibility (S) rates for US surveillance data that these IC changes created. Methods Clinical isolates (reference broth microdilution MIC) from 2016–2018 US SENTRY Program were analyzed for S based on current and previous IC. FQ results for ciprofloxacin (CIP), levofloxacin (LEV), and moxifloxacin (MOX) were evaluated. Benchmark S comparison data for meropenem, cefepime, piperacillin–tazobactam and delafloxacin (new FQ) were also included. Results S rates for Enterobacteriaceae (ENT;Figure) were reduced by 3.8/3.7% for CIP/LEV (CLSI) and 2.3/2.5% (EUCAST). MOX-S rate vs. ENT declined 5.7% (EUCAST). Although reductions in S occurred for most organism groups, K. pneumoniae (6.0/5.5% for CIP/LEV [CLSI] and 4.0/4.2% [EUCAST]) and S. marcescens (7.4/4.1% for CIP/LEV [CLSI] and 4.1/5.0% [EUCAST]) reductions were among the largest changes. For Pseudomonas aeruginosa (PSA), CIP-S decreased 6.8% and LEV-S 10.1% (CLSI); but potential for false-S results remain using CLSI IC (5 pathogens). Conclusion USCAST’s comprehensive analyses of FQ IC in 2015 led to revised breakpoints for most organism/drug combinations among ENT and PSA compared with those being used before. USCAST analysis was most influenced by PK/PD in vivo data as current clinical outcomes data by MIC was limited. Awareness and interactions (both formal and informal) among breakpoint setting organizations has modified FQ ICs which are lower than previously recommended, and although not perfectly harmonized in time and detail, this represents a successful model. Disclosures All authors: No reported disclosures.

Ventilator-associated bacterial pneumonia (VABP) is a difficult therapeutic problem. Considerable controversy exists regarding the optimal chemotherapy for this entity. The recent guidelines of the Infectious Diseases Society of America and the American Thoracic Society recommend a 7-day therapeutic course for VABP based on the balance of no negative impact on all-cause mortality, less resistance emergence, and fewer antibiotic treatment days, counterbalanced with a higher relapse rate for patients whose pathogen is a nonfermenter. The bacterial burden causing an infection has a substantial impact on treatment outcome and resistance selection. We describe the baseline bronchoalveolar lavage (BAL) fluid burden of organisms in suspected VABP patients screened for inclusion in a clinical trial. We measured the urea concentrations in plasma and BAL fluid to provide an index of the dilution of the bacterial and drug concentrations in the lung epithelial lining fluid introduced by the BAL procedure. We were then able to calculate the true bacterial burden as the diluted colony count times the dilution factor. The median dilution factor was 28.7, with the interquartile range (IQR) being 11.9 to 53.2. Median dilution factor-corrected colony counts were 6.18 log 10 (CFU/ml) [IQR, 5.43 to 6.46 log 10 (CFU/ml)]. In a subset of patients, repeat BAL on day 5 showed a good stability of the dilution factor. We previously showed that large bacterial burdens reduce or stop bacterial killing by granulocytes. (This study has been registered at ClinicalTrials.gov under registration no. NCT01570192.)

Ceftaroline is a cephalosporin with broad-spectrum in vitro activity against pathogens commonly associated with acute bacterial skin and skin structure infections (ABSSSI), including methicillin-resistant Staphylococcus aureus . Ceftaroline fosamil, the prodrug of ceftaroline, is approved for the treatment of patients with ABSSSI. Using data from the microbiologically evaluable population from two phase 2 and two phase 3 randomized, multicenter, double-blind studies of patients with ABSSSI, an analysis examining the relationship between drug exposure, as measured by the percentage of time during the dosing interval that free-drug steady-state concentrations remain above the MIC ( f % T >MIC), and clinical and microbiological responses was undertaken. The analysis population included 526 patients, of whom 423 had infections associated with S. aureus . Clinical and microbiological success percentages were 94.7 and 94.5%, respectively, among all of the patients and 95.3 and 95.7%, respectively, among those with S. aureus infections. Univariable analysis based on data from all of the patients and those with S. aureus infections demonstrated significant relationships between f % T >MIC and microbiological response ( P < 0.001 and P = 0.026, respectively). Multivariable logistic regression analyses demonstrated other patient factors in addition to f % T >MIC to be significant predictors of microbiological response, including age and infection type for all of the patients evaluated and age, infection type, and the presence of diabetes mellitus for patients with S. aureus infections. Results of these analyses confirm that a ceftaroline fosamil dosing regimen of 600 mg every 12 h provides exposures associated with the upper plateau of the pharmacokinetic-pharmacodynamic relationship for efficacy.

CD101 is a novel echinocandin with concentration-dependent fungicidal activity in vitro and a long half-life (∼133 h in humans, ∼70 to 80 h in mice). Given these characteristics, it is likely that the shape of the CD101 exposure (i.e., the time course of CD101 concentrations) influences efficacy. To test this hypothesis, doses which produce the same total area under the concentration-time curve (AUC) were administered to groups of neutropenic ICR mice infected with Candida albicans R303 using three different schedules. A total CD101 dose of 2 mg/kg was administered as a single intravenous (i.v.) dose or in equal divided doses of either 1 mg/kg twice weekly or 0.29 mg/kg/day over 7 days. The studies were performed using a murine disseminated candidiasis model. Animals were euthanized at 168 h following the start of treatment. Fungi grew well in the no-treatment control group and showed variable changes in fungal density in the treatment groups. When the CD101 AUC from 0 to 168 h (AUC 0–168 ) was administered as a single dose, a >2 log 10 CFU reduction from the baseline at 168 h was observed. When twice-weekly and daily regimens with similar AUC values were administered, net fungal stasis and a >1 log 10 CFU increase from the baseline were observed, respectively. These data support the hypothesis that the shape of the CD101 AUC influences efficacy. Thus, CD101 administered once per week demonstrated a greater degree of fungal killing than the same dose divided into twice-weekly or daily regimens.

Vaborbactam is a member of a new class of β-lactamase inhibitors with inhibitory activity against serine carbapenemases (e.g., Klebsiella pneumoniae carbapenemase) that has been developed in combination with meropenem. The pharmacokinetics of the combination was evaluated in 41 subjects with chronic renal impairment in a phase 1, open-label, single-dose study. Subjects were assigned to one of five groups based on renal function: normal (creatinine clearance of ≥90 ml/min), mild (estimated glomerular filtration rate [eGFR] of 60 to 89 ml/min/1.73 m 2 ), moderate (eGFR of 30 to P < 0.001) and vaborbactam (mean of 5.11-fold increase, P = 0.0235) relative to drug administration off dialysis, consistent with dose recovery rates of 38.3% and 52.9% for meropenem and vaborbactam, respectively, in dialysate. Plasma clearance of meropenem and vaborbactam is reduced with renal impairment, requiring dose adjustment. Hemodialysis removes both drugs. (This study has been registered at ClinicalTrials.gov under identifier NCT02020434.)

The pharmacokinetic-pharmacodynamic (PK-PD) relationships between serum exposure measures of liposomal amikacin for inhalation (LAI) and the change in pulmonary function test (PFT) measures and number of CFU from baseline were evaluated in cystic fibrosis (CF) patients chronically infected with Pseudomonas aeruginosa . A dose of 70, 140, 280, or 560 mg of LAI or placebo was administered to CF patients once daily for 28 days. PFTs and sputum samples for microbiology were assessed on days 7, 14, 21, 28, 35 (for log 10 CFU), and 56 (for PFTs). Serum, urine, and sputum samples were collected for PK evaluation. The relationships between efficacy endpoints (relative change in forced expiratory volume in 1 s [FEV 1 {expressed in liters}] and FEV 1 % predicted and the absolute change in log 10 CFU of P. aeruginosa from baseline) and exposure measures (dose, day 1 area under the curve [AUC], dose/MIC ratio, and day 1 AUC/MIC ratio) and baseline MIC value were assessed. The serum and urine PK data were best fit by a 3-compartment model (lung, serum, and urine) with linear clearance and interoccasional variation on total and renal clearance. Significant univariable relationships between dose or day 1 AUC and the relative change in PFT measures ( P ≤ 0.017) or the absolute change in log 10 CFU from baseline ( P ≤ 0.037) on the study days were identified. Repeated-measures mixed-effects models, which showed dose- and AUC-related improvements for each efficacy endpoint ( P ≤ 0.041), predicted the observed data well. The increases in the relative change in FEV 1 and FEV 1 % predicted of 11% and 9.9%, respectively, and a 1.23-log 10 CFU reduction per 560 mg of LAI estimated on day 7 were comparable to the observed increases of 10.7% and 10.3%, respectively, and a 1.24-log 10 CFU reduction on the same day. The model-estimated PFT effects were predicted to be sustained to day 28. An additional 0.451-log 10 CFU reduction ( P = 0.022) was estimated on day 14 relative to day 7, with a persistence of effect predicted to day 35.

To provide support for in vitro susceptibility test interpretive criteria decisions for ceftaroline against Staphylococcus aureus and Streptococcus pneumoniae , as well as dose adjustment recommendations for renal impairment, pharmacokinetic-pharmacodynamic (PK-PD) target attainment was evaluated for simulated patients administered intravenous (i.v.) ceftaroline fosamil at 600 mg twice daily (q12h) and simulated patients with renal impairment administered various dosing regimens. Using a previously developed population PK model, Monte Carlo simulation was used to generate ceftaroline plasma concentration profiles for simulated patients with normal renal function or mild, moderate, or severe renal impairment. Using these profiles, the percentage of time during the dosing interval that free-drug concentrations remained above the MIC ( f % T >MIC) for ceftaroline at steady state was calculated. Percentages of simulated patients achieving f % T >MIC targets for S. aureus and S. pneumoniae based on murine infection models were calculated by MIC. At MICs of 2 mg/liter for S. aureus and 1 mg/liter for S. pneumoniae , the percentages of simulated patients with normal renal function and mild renal impairment following administration of ceftaroline fosamil at 600 mg q12h, moderate renal impairment following administration of ceftaroline fosamil at 400 mg q12h, and severe renal impairment following administration of ceftaroline fosamil at 300 mg q12h achieving f % T >MIC targets (≥26 for S. aureus and ≥44 for S. pneumoniae ) exceeded 90%. The results of these analyses, which suggested that in vitro susceptibility test interpretive criteria defining susceptible could be as high as MICs of ≤2 and ≤1 mg/liter for ceftaroline against S. aureus and S. pneumoniae , respectively, provide support for current FDA and CLSI criteria, which define susceptible as MICs of 1 and 0.5 mg/liter, respectively. Recommendations for dose adjustments for patients with renal impairment were also supported by the results of these analyses.

Background RZF is a novel antifungal of the echinocandin class with distinctive pharmacokinetics that support weekly dosing intervals. RZF is being developed for the treatment of candidemia and invasive candidiasis (IC) and the prevention of invasive fungal infections. A previously developed population PK model based on Phase 1 intravenous (IV) data [AAC 2018; e02603–17] was refined using IV data from additional Phase 1 and Phase 2 (STRIVE) studies. Methods Data from the two Phase 1 studies used previously to develop the model were pooled with data from an additional Phase 1 study and the STRIVE trial in patients with candidemia and/or IC. The population PK model was refined using NONMEM Version 7.2. The ability of covariates such as body size, age, sex, albumin, markers of liver and renal function, and infection status to explain a portion of the interindividual variability on select PK parameters was explored using stepwise forward selection (α = 0.01) and backward elimination (α = 0.001). The final model was externally validated by comparing model-based predictions to observed data from STRIVE, which were not available during model development. Results The final population PK model was a linear, four-compartment model with zero order IV input. Albumin was the most important predictor of the interindividual variability in RZF PK as significant relationships were found between serum albumin concentration and clearance, volume of the central compartment, volume of peripheral compartment 1, and volume of peripheral compartment 2. Additional relationships were found between PK parameters and sex, body weight, and infection status. The model provided precise and unbiased fits to the observed data (Figure 1). Differences in predicted median AUC across a wide range of covariate values were modest (Figure 2). The final model was also able to predict the central tendency and variability in RZF concentration–time data from patients with candidemia and/or IC not included in the model development (Figure 3). Conclusion A population PK model describing RZF PK in healthy subjects and patients with candidemia and/or IC was successfully developed. This model was utilized for subsequent PK-PD target attainment analyses to support dose selection for RZF. Disclosures E. A. Lakota, Cidara Therapeutics: Research Contractor, Research support. H. Ganesan, Cidara Therapeutics: Research Contractor, Research support. S. Flanagan, Cidara Therapeutics: Employee and Shareholder, Salary and stock options. V. Ong, Cidara Therapeutics: Employee and Shareholder, Salary and Stock options. T. Sandison, Cidara Therapeutics: Employee and Shareholder, Salary and Stock options. S. M. Bhavnani, Cidara Therapeutics: Research Contractor, Research support. C. M. Rubino, Cidara Therapeutics: Research Contractor, Research support. P. G. Ambrose, Cidara Therapeutics: Research Contractor, Research support.

Background ME1100 (arbekacin inhalational solution) is an aminoglycoside in clinical development for the treatment of patients with hospital-acquired and ventilator-associated bacterial pneumonia (HABP and VABP, respectively). Due to the increase in resistance of Staphylococcus aureus and Pseudomonas aeruginosa to many antimicrobial agents, it is important to understand the relationships between amplification of drug resistance and each of drug exposure and therapy duration. The objective of the studies described herein was to utilize the HFIM to determine the arbekacin exposure after ME1100 administration required to prevent the emergence of drug-resistant subpopulations. Methods Duplicate 10-day HFIM assays were completed in which arbekacin total-drug epithelial lining fluid (ELF) concentration–time profiles following inhalational administration of ME1100 every 12 hours were simulated. Four isolates, two methicillin-resistant S. aureus (Arbekacin MIC = 1 mg/L), and two P. aeruginosa (Arbekacin MIC = 4 mg/L), were exposed to total-drug ELF area under the concentration–time curve (AUC) values ranging from 217 to 25,053 mg hour/L, which were simulated using two different half-lives, 1 hour (α) and 6.93 hours (β). The initial bacterial burden was 1.0 × 108 CFU/mL. Samples were collected for enumeration of both the total and drug-resistant bacterial burdens and evaluation of pharmacokinetic samples using LC/MS–MS. Results Total-drug ELF AUC:MIC ratios required to prevent amplification of MRSA and P. aeruginosa resistance in the HFIM over 10 days were 1,512 and 2,942, respectively. The higher AUC:MIC ratio required to prevent resistance for P. aeruginosa was most likely due to the presence of a small colony variant population. The relationship between total-drug ELF AUC:MIC ratio and change in log10 CFU from baseline of the drug-resistant sub-populations found on agar plates on Day 10 took the form of an inverted-U for three pathogens and a step-function for one (Figure 1). Conclusion These data, which address the goal of considering arbekacin exposures that prevent the development of on-therapy resistance in a clinical setting, will help to provide guidance for future ME1100 dose selection for the treatment of patients with HABP/VABP. Disclosures B. D. VanScoy, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. E. A. Lakota, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. S. M. Bhavnani, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. G. Giesel, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. A. I. Carranco, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. Y. Nagira, Meiji Seika Pharma Co. Ltd.: Employee, Salary. S. Ouchi, Meiji Seika Pharma Co. Ltd.: Employee, Salary. K. Kondo, Meiji Seika Pharma Co. Ltd.: Employee, Salary. P. G. Ambrose, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support.

Background ME1100 (arbekacin inhalational solution) is an inhaled aminoglycoside being developed to treat patients with hospital-acquired and ventilator-associated bacterial pneumonia (HABP and VABP, respectively). PK-PD target attainment analyses were undertaken to evaluate ME1100 regimens for patients with HABP/VABP arising from Klebsiella pneumoniae (KP), Pseudomonas aeruginosa (PA) and Staphylococcus aureus (SA), including those with renal impairment. Methods Data used included a population pharmacokinetic (PPK) model developed using Phase 1 and post-marketing PK data, nonclinical PK-PD targets from one compartment in vitro and/or in vivo infection models, and MIC data. Using parameter estimates from the PPK model (four-compartment model with first-order elimination), total-drug epithelial lining fluid concentration-time profiles were generated for simulated patients with varying creatinine clearance (CLcr; mL/minute/1.73 m2) and by CLcr group. Twice daily (BID) ME1100 regimens ranging from 300 to 900 mg were assessed in simulated patients with CLcr >80 to ≤120 mL/minute/1.73 m2. Percent probabilities of PK-PD target attainment by MIC were determined based on total-drug ELF AUC:MIC ratio targets associated with 1- and 2-log10 CFU reductions from baseline for KP, PA and SA using Day 1 AUC. Regimens in simulated patients with renal impairment that best matched the BID regimen in the normal CLcr group with high percent probabilities of PK-PD target attainment and a low percent probability of Cmin > 2 mg/L were identified. Results ME1100 600 mg BID in simulated patients with CLcr >80 to ≤120 mL/minute/1.73 m2, with 600 mg once daily, 450 mg BID and 600 mg BID in simulated patients with CLcr of 0 to ≤30, >30 to ≤50 and >50 to ≤80 mL/minute/1.73 m2, respectively, achieved high percent probabilities of PK-PD target attainment based on PK-PD targets for a 1-log10 CFU reduction from baseline at relevant MIC values for KP, PA and SA, and relatively lower Cmin values. In simulated patients with varying CLcr who received these regimens, high percent probabilities of PK-PD target attainment were achieved for KP, PA and SA at the upper margins of the MIC distributions (Figures 1–3). Conclusion The data provide support for ME1100 dose selection for patients with HABP/VAPB. Disclosures S. M. Bhavnani, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. J. P. Hammel, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. E. A. Lakota, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. B. D. VanScoy, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. Y. Nagira, Meiji Seika Pharma Co. Ltd.: Employee, Salary. C. M. Rubino, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support. N. Sato, Meiji Seika Pharma Co. Ltd.: Employee, Salary. T. Koresawa, Meiji Seika Pharma Co. Ltd.: Employee, Salary. K. Kondo, Meiji Seika Pharma Co. Ltd.: Employee, Salary. P. G. Ambrose, Meiji Seika Pharma Co. Ltd.: Research Contractor, Research support.

Background In 2016 USCAST, the National Advisory Committee (NAC) for the United States (US) to EUCAST, undertook the re-evaluation of the in vitro susceptibility (AST) test interpretive criteria (IC) for gentamicin (GM), tobramycin (TO) and amikacin (AK) against Enterobacteriaceae (ENT), P. aeruginosa (PSA) and S. aureus (SA) based on an analysis of contemporary microbiology and PK/PD data. In 2019 USCAST posted the third version (www.uscast.org) of AG IC document and CLSI and EUCAST has published AG IC in CLSI M100-S29 and EUCAST v 9.0 documents. USCAST ICs for S were generally lower than those proposed by CLSI for all organism/drug combinations. PK/PD emphasized high, extended interval dosing (5 renal function groups) to reduce nephro-vestibular toxicity and a stasis exposure endpoint. Here, we evaluate the impact on S rates for US AST data that these IC changes created. Methods Clinical isolates from 2010 to 2018 US SENTRY Program (reference broth microdilution AST) were analyzed for S based on current and previous IC values. AG results for GM, TO and AK were evaluated against 66,280 ENT, 13,959 PSA and 51,950 SA. Benchmark S data for meropenem, cefepime, piperacillin–tazobactam and new AG, plazomicin (PZM) were included as well as ESBL and carbapenem-resistant ENT (CRE; 805 isolates). Results S rates for ENT as determined by USCAST IC were reduced by 4.2/1.2/3.1% for AK/GM/TO (CLSI) and by 3.3% for AK (EUCAST); no S rate difference for GM and TO as determined by USCAST/EUCAST. For PSA, S decreased by 46.8/6.2% for AK/TO (EUCAST) and 51.6/6.2% (CLSI). S for SA vs. GM declined by only 0.2% (CLSI). No AG IC could be calculated/offered for Acinetobacter or GM X PSA or AM/TO X SA. Best S overall coverage X ESBL (99.2%) or CRE (97.2%) isolates was by PZM. Conclusion USCAST IC updates for AG lead to reduced values for some organism/drug combinations among ENT and PSA compared with those proposed elsewhere. The USCAST-recommended ICs were based on achieving AUC/MIC ratio target associated with net bacterial stasis. Given the assumption of AG combination therapy, stasis was considered a reasonable endpoint when evaluating AG ICs to improve both safety and efficacy. Some organism X drug exposures could not be calculated and lower IC for pneumonia isolates (GM, TO) was recommended. Disclosures All authors: No reported disclosures.

Background Polymyxins are important antimicrobial agents for the treatment of infections due to carbapenem-resistant and other multidrug-resistant organisms. Recently, the CLSI and EUCAST have set breakpoints for colistin (EUCAST and CLSI) and polymyxin B (CLSI) with slight differences in recommendations. However, there are issues unique to the polymyxin class that warrant additional guidances. Herein, we assess data related to breakpoint setting and make additional recommendations for polymyxin AST interpretive criteria. Methods Data sources included longitudinal (2011–2017) US surveillance reference broth microdilution (BMD) MIC distributions (128,573 isolates) for colistin and polymyxin B (PB), published data on accuracy of various AST methodologies, in vivo pharmacokinetic/pharmacodynamic (PK-PD) models, prior polymyxin guidelines and agency package insert dosing recommendations, and population PK-PD and toxicodynamic (TD) data. Epidemiological cut-off, PK-PD (and TD), and clinical data were all considered for susceptible (S) breakpoint determinations. Results Data demonstrate that the most commonly utilized AST methodologies (disk diffusion, Etest, and automated MIC susceptibility panels), as well as agar dilution testing cannot reliably detect resistance; and BMD is the preferred AST. Importantly, colistin S is a reliable surrogate for PB S with cross-S accuracy at > 99% of isolates in each pathogen group. Breakpoint recommendations can be found in the Table with emphasis on applying combination therapy. Key recommendations include an S breakpoint of ≤2 mg/L for each pathogen (both colistin and PB). However, based on a lack of preclinical efficacy in murine pneumonia models, PK/PD concerns, and poor clinical outcome data, we strongly suggest that no breakpoints are applied for pneumonia and that alternative therapies should be used where available. Additionally, due to a lack of significant renal excretion, PB will also have no S breakpoint recommendation for lower urinary tract infections. Conclusion The polymyxins have compromising characteristics that make them suboptimal antimicrobials when used alone, and additional caveats are required for AST breakpoint interpretive criteria and stewardship programs. Disclosures All authors: No reported disclosures.

Oseltamivir is a potent inhibitor of influenza virus neuraminidase enzymes essential for viral replication. This study aimed to investigate the impact of covariates on pharmacokinetic (PK) variability of oseltamivir and its active metabolite form, oseltamivir carboxylate (OC). Dosing history, plasma drug concentrations, and demographic information were pooled from 13 clinical trials providing data for 390 healthy and infected subjects ranging in age from 1 to 78 years and given oseltamivir doses of 20 to 1,000 mg. Candidate population PK models simultaneously characterizing the time course of oseltamivir and OC in plasma were evaluated by using the NONMEM software program, and subject covariates were assessed using stepwise forward selection (α = 0.01) and backward elimination (α = 0.001). A two-compartment model with first-order absorption of oseltamivir and first-order conversion of oseltamivir to OC and a one-compartment model with first-order elimination of OC were utilized. Body weight when evaluated using a power function was a significant predictor of the apparent oseltamivir clearance and both apparent OC clearance (CL m /F) and central volume of distribution (Vc m /F). Creatinine clearance was a significant predictor of CL m /F, while Vc m /F also decreased linearly with age. A visual predictive check indicated that the final model described oseltamivir and OC concentrations in plasma adequately across dose regimens and subject covariate ranges. Concordance of population mean and individual post hoc predictions of maximum concentration of drug at steady state ( C max ) and area under the plasma drug concentration-time curve from 0 to 24 h at steady state (AUC 0–24 ) was high ( r 2 = 0.81 and 0.71, respectively). In conclusion, a comprehensive population PK model was constructed to bridge the adult to pediatric oseltamivir PK data, allowing for reasonable estimation of the PK of OC using subject demographic data alone.

Widespread resistance in Enterobacteriaceae and Pseudomonas aeruginosa to cephalosporin and monobactam antibiotics due to extended-spectrum β-lactamases (ESBLs) has resulted in the need for reassessment of the interpretative criteria (breakpoints) established for these agents more than 2 decades ago. Following extensive evaluation, the Clinical and Laboratory Standards Institute recently adopted and published new breakpoints for these agents for use in clinical laboratories and provided updated recommendations for use of the ESBL screening test. This paper summarizes the background and supportive rationale for new interpretative criteria for cephalosporins and aztreonam for testing Enterobacteriaceae.

The objectives of this analysis were to develop a population pharmacokinetic (PK) model to describe the absorption and disposition of fusidic acid after single and multiple doses and to determine the effect of food on the rate and extent of bioavailability. Plasma PK data from three phase 1 studies ( n = 75; n = 14 with and without food) in which healthy subjects received sodium fusidate (500 to 2,200 mg) as single or multiple oral doses every 8 h (q8h) or q12h for up to 7 days were modeled using S-ADAPT (MCPEM algorithm). Accumulation of fusidic acid after multiple doses was more than that predicted based on single-dose data. The PK of fusidic acid was best described using a time-dependent mixed-order absorption process, two disposition compartments, and a turnover process to describe the autoinhibition of clearance. The mean total clearance (% coefficient of variation) was 1.28 liters/h (33%) and the maximum extent of autoinhibition was 71.0%, with a 50% inhibitory concentration (IC 50 ) of 46.3 mg/liter (36%). Food decreased the extent of bioavailability by 18%. As a result of the autoinhibition of clearance, steady state can be achieved earlier with dosing regimens that contain higher doses (after 8 days for 750 mg q12h and 1 day for 1,500 mg q12h on day 1 followed by 600 mg q12h versus 3 weeks for 500 mg q12h). Given that large initial doses autoinhibit the clearance of fusidic acid, this characteristic provides a basis for the administration of front-loaded dosing regimens of sodium fusidate which would allow for effective concentrations to be achieved early in therapy.

Antimicrobial stewardship programs face many challenges, one of which is a lack of guidance regarding antimicrobial dose, interval, and duration. There is no tool that considers patient demographic, pathogen susceptibility, and pharmacokinetic-pharmacodynamic (PK-PD) targets for efficacy in order to evaluate appropriate antimicrobial dosing regimens. The PK-PD Compass, an educational mobile application, was developed to address this unmet need. The application consists of a Monte Carlo simulation algorithm which integrates pharmacokinetic (PK) and PK-PD data, patient-specific characteristics, and pathogen susceptibility data. Through the integration of these data, the application allows practitioners to assess the percent probability of PK-PD target attainment for 35 intravenous antimicrobial agents across 29 infection categories. Population PK models for each drug were identified, evaluated, and refined as needed. Susceptibility breakpoints were based upon FDA and CLSI criteria. By incorporating these data into one interface, clinicians can select the infection, pathogen, and antimicrobial agents of interest and obtain the percent probability of PK-PD target attainment for each regimen based upon patient-specific characteristics. The antimicrobial dosing regimens provided include those recommended by standard guidelines and reference texts. However, unlike these references, potential choices are prioritized based on percent probabilities of PK-PD target attainment. Such data will educate clinicians on selecting optimized antibiotic regimens through the lens of PK-PD.

We have previously demonstrated the pharmacokinetic-pharmacodynamic (PK-PD) index best associated with the efficacy of tazobactam when used in combination with ceftolozane to be the percentage of the dosing interval during which tazobactam concentrations remained above a threshold value (%time>threshold). Using an in vitro infection model and the same isogenic CTX-M-15-producing Escherichia coli triplet set genetically engineered to transcribe different levels of bla CTX-M-15 , herein we describe dose fractionation studies designed to evaluate the PK-PD index associated with tazobactam efficacy, when given in combination with piperacillin, and the impact of the presence of a different β-lactam agent, or different bla CTX-M-15 transcription levels, on the magnitude of the tazobactam PK-PD index necessary for efficacy. The recombinant strains demonstrated piperacillin MIC values of 128, >256, and >256 μg/ml for the low-, moderate-, and high-level CTX-M-15-producing E. coli strains, respectively. The MIC value for piperacillin in the presence of 4 μg/ml of tazobactam was 2 μg/ml for all three strains. The PK-PD index associated with tazobactam efficacy was confirmed to be %time>threshold, regardless of β-lactamase transcription ( r 2 = 0.839). The tazobactam concentration thresholds, however, changed with the CTX-M-15 transcription level and were 0.25, 0.5, and 2 μg/ml for the low-, moderate-, and high-level CTX-M-15-producing strains, respectively ( r 2 = 0.921, 0.773, and 0.875, respectively). The %time>threshold values for tazobactam necessary for net bacterial stasis and a 1- and 2-log 10 -unit CFU/ml decrease from baseline at 24 h were 44.9, 62.9, and 84.9%, respectively. In addition to verifying our previous study results, these results also demonstrated that the magnitude of bacterial-cell killing associated with a β-lactam–β-lactamase inhibitor combination is dependent on the amount of β-lactamase produced. These data provide important information for the development of β-lactam–β-lactamase inhibitor combination agents.