Antimicrobial Resistance: Pharmacokinetics‐Pharmacodynamics of Antimicrobial Therapy: It’s Not Just for Mice Anymore

Intrapulmonary Pharmacokinetics of Levonadifloxacin following Oral Administration of Alalevonadifloxacin to Healthy Adult Subjects

Alalevonadifloxacin (WCK 2349) is a novel l-alanine ester prodrug of levonadifloxacin that is being developed as an oral fluoroquinolone antibiotic. The primary objective of this study was to determine and compare plasma, epithelial lining fluid (ELF), and alveolar macrophage (AM) concentrations of levonadifloxacin following oral administration of alalevonadifloxacin to healthy adult subjects. Levonadifloxacin concentrations in plasma, ELF, and AM samples from 30 healthy subjects were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) following oral dosing of alalevonadifloxacin (1,000 mg twice daily for 5 days). Six subjects were assigned to each bronchoalveolar lavage (BAL) fluid sampling time, i.e., 2, 4, 6, 8, or 12 h after the ninth oral dose. Noncompartmental pharmacokinetic (PK) parameters were determined from serial total plasma concentrations collected over a 12-h interval following the first and ninth oral doses. Penetration ratios were calculated from the areas under the concentration-time curves from 0 to 12 h (AUC_0-12) for plasma, ELF, and AM by using mean (and median) concentrations at each BAL sampling time. Unbound plasma concentrations (∼85% plasma protein binding) were used to determine site-to-plasma penetration ratios. Plasma PK parameter values for levonadifloxacin were similar after the first and ninth doses. The respective AUC_0-12 values based on mean ELF and AM concentrations were 172.6 and 35.3 mg · h/liter, respectively. The penetration ratios for ELF and AM levonadifloxacin concentrations to unbound plasma levonadifloxacin concentrations were 7.66 and 1.58, respectively. Similar penetration ratios were observed with median concentrations. The observed plasma, ELF, and AM concentrations of levonadifloxacin support further studies of alalevonadifloxacin for treatment of lower respiratory tract bacterial infections caused by susceptible pathogens. (This study has been registered at ClinicalTrials.gov under identifier NCT02253342.).

Pharmacodynamics of cefiderocol, a novel siderophore cephalosporin, in a Pseudomonas aeruginosa neutropenic murine thigh model

Cefiderocol is a siderophore cephalosporin that displays potent in vitro activity against multidrug-resistant (MDR) Gram-negative bacteria. This study aimed to describe the pharmacokinetics, pharmacodynamics and 24-h efficacy of cefiderocol using dose-ranging methods in a neutropenic murine thigh infection model. Infection was established in neutropenic mice (administered cyclophosphamide 150 mg/kg and 100 mg/kg at 4 days and 1 day prior to inoculation, respectively) with eight Pseudomonas aeruginosa isolates [minimum inhibitory concentration (MIC) range 0.063-0.5 µg/mL] that displayed variable in vivo activity against previously tested β-lactams with siderophore moieties. Renal excretion was controlled by administration of 5 mg/kg uranyl nitrate 3 days prior to inoculation. Cefiderocol was administered subcutaneously in eight escalating doses [4.2-166.7 mg/kg every 8 h (q8h)]. In pharmacokinetic studies, cefiderocol manifested similar pharmacokinetics across tested doses (4, 100 and 250 mg/kg) with a mean half-life of 0.86 h. In pharmacodynamic studies, the change in CFU after 24 h from the initial inoculum ranged from +3.4 to -3.1 log10 with doses of 4.2-166.7 mg/kg q8h. Dose-response curves for the eight isolates assumed the characteristic sigmoidal shape, with greater CFU reductions as the dose increased. Focusing on the previously defined efficacy parameter of fT>MIC (time that the free drug concentration exceeds the MIC) for this compound, targets for stasis and 1 log10 and 2 log10 reductions ranged from 44.4-94.7, 50.2-97.5 and 62.1-100, respectively. Cefiderocol displayed sustained antibacterial effects against these MDR P. aeruginosa isolates. These data support the cefiderocol dose selected for clinical trials.

Population Pharmacokinetic Model-Based Evaluation of Standard Dosing Regimens for Cefuroxime Used in Coronary Artery Bypass Graft Surgery with Cardiopulmonary Bypass

The purpose of this study was to investigate the population pharmacokinetics (PK) of cefuroxime in patients undergoing coronary artery bypass graft (CABG) surgery. In this observational pharmacokinetic study, multiple blood samples were collected over a 48-h interval of intravenous cefuroxime administration. The samples were analyzed by using a validated high-performance liquid chromatography (HPLC) method. Population pharmacokinetic models were developed using Monolix (version 4.4) software. Pharmacokinetic-pharmacodynamic (PD) simulations were performed to explore the ability of different dosage regimens to achieve the pharmacodynamic targets. A total of 468 blood samples from 78 patients were analyzed. The PK for cefuroxime were best described by a two-compartment model with between-subject variability on clearance, the volume of distribution of the central compartment, and the volume of distribution of the peripheral compartment. The clearance of cefuroxime was related to creatinine clearance (CL_CR). Dosing simulations showed that standard dosing regimens of 1.5 g could achieve the PK-PD target of the percentage of the time that the free concentration is maintained above the MIC during a dosing interval (fT_MIC) of 65% for an MIC of 8 mg/liter in patients with a CL_CR of 30, 60, or 90 ml/min, whereas this dosing regimen failed to achieve the PK-PD target in patients with a CL_CR of ≥125 ml/min. In conclusion, administration of standard doses of 1.5 g three times daily provided adequate antibiotic prophylaxis in patients undergoing CABG surgery. Lower doses failed to achieve the PK-PD target. Patients with high CL_CR values required either higher doses or shorter intervals of cefuroxime dosing. On the other hand, lower doses (1 g three times daily) produced adequate target attainment for patients with low CL_CR values (≤30 ml/min).

Assessment of in vivo efficacy of eravacycline against Enterobacteriaceae exhibiting various resistance mechanisms: a dose-ranging study and pharmacokinetic/pharmacodynamic analysis

After the pharmacokinetic (PK) profile of eravacycline, a novel fluorocycline, was defined, understanding its pharmacodynamic (PD) profile became essential. This study aimed to assess the correlation of the PK/PD index fAUC/MIC (ratio of area under the free drug concentration-time curve to MIC) and its magnitude with eravacycline's efficacy against Enterobacteriaceae using an immunocompetent murine thigh infection model to resemble the immunocompetent environment in eravacycline's clinical trials. Eight Enterobacteriaceae isolates with various resistance mechanisms were tested. Eravacycline doses ranged from 1-10 mg/kg/day and were given either once daily (q24h) or divided into doses every 12 h (q12h) over the 24-h treatment period. Antibacterial efficacy was measured as the change in log₁₀CFU at 24 h compared with 0 h controls. Composite data were modelled using a sigmoid E_max model. Eravacycline MICs ranged from 0.125-0.5 µg/mL. The mean fAUC/MIC magnitudes required for stasis and 1-log reduction for the eight isolates were 2.9 ± 3.1 and 5.6 ± 5.0, respectively. Whilst the humanised eravacycline regimen (2.5 mg/kg q12h) pharmacokinetically achieves an fAUC_0-24 that is higher than the fAUC_0-24 achieved with the 5 mg/kg q24h dose, the latter was associated with greater efficacy, raising a suggestive correlation of the peak free drug concentration to MIC (fC_max/MIC) ratio with eravacycline's efficacy. This study showed that the magnitudes associated with eravacycline's efficacy in an immunocompetent murine thigh model appear to be close to achievable targets in human. These data support further development of eravacycline for treatment of infections caused by drug-resistant Enterobacteriaceae.

Determining β-lactam exposure threshold to suppress resistance development in Gram-negative bacteria

Objectives

β-Lactams are commonly used for nosocomial infections and resistance to these agents among Gram-negative bacteria is increasing rapidly. Optimized dosing is expected to reduce the likelihood of resistance development during antimicrobial therapy, but the target for clinical dose adjustment is not well established. We examined the likelihood that various dosing exposures would suppress resistance development in an in vitro hollow-fibre infection model.

Methods

Two strains of Klebsiella pneumoniae and two strains of Pseudomonas aeruginosa (baseline inocula of ∼10 8  cfu/mL) were examined. Various dosing exposures of cefepime, ceftazidime and meropenem were simulated in the hollow-fibre infection model. Serial samples were obtained to ascertain the pharmacokinetic simulations and viable bacterial burden for up to 120 h. Drug concentrations were determined by a validated LC-MS/MS assay and the simulated exposures were expressed as C min /MIC ratios. Resistance development was detected by quantitative culture on drug-supplemented media plates (at 3× the corresponding baseline MIC). The C min /MIC breakpoint threshold to prevent bacterial regrowth was identified by classification and regression tree (CART) analysis.

Results

For all strains, the bacterial burden declined initially with the simulated exposures, but regrowth was observed in 9 out of 31 experiments. CART analysis revealed that a C min /MIC ratio ≥3.8 was significantly associated with regrowth prevention (100% versus 44%, P  = 0.001).

Conclusions

The development of β-lactam resistance during therapy could be suppressed by an optimized dosing exposure. Validation of the proposed target in a well-designed clinical study is warranted.

Efficient Delivery of Investigational Antibacterial Agents via Sustainable Clinical Trial Networks

The economics of antibiotics can be improved by infectious diseases–specific clinical trial networks. While developers would still need to implement an independent phase 1 program as well as studies focused on highly resistant pathogens, standardized procedures in a network focused on usual drug resistance phenotype isolates would permit sharing of controls and would predictably generate high-quality pivotal data for product registration while creating cost and time savings in the range of 30%–40%. This would reduce economic barriers to antibiotic development and contribute to public health.

Partnerships to Design Novel Regimens to Treat Childhood Tuberculosis, Sui Generis: The Road Ahead

There has been a recent expansion of preclinical models to predict the efficacy of regimens to treat adults with tuberculosis. Despite increasing global interest in childhood tuberculosis, these same tools have not been employed to develop pediatric regimens. Children differ from adults in bacillary burden, spectrum of disease, the metabolism and distribution of antituberculosis drugs, and the toxicity experienced. The studies documented in this series describe a proof-of-concept approach to pediatric regimen development. We propose a program of investigation that would take this forward into a systematic and comprehensive method to find optimal drug combinations to use in children, ideal exposures, and required dosing. Although the number of possible drug combinations is extensive, a series of principles could be employed to select likely effective regimens. Regimens should avoid drugs with overlapping toxicity or linked mechanisms of resistance and should aim to include drugs with different mechanisms of action and ones that are able to target different subpopulations of mycobacteria. Finally drugs should penetrate into body sites necessary for treating pediatric disease. At an early stage, this body of work would need to engage with regulatory agencies and bodies that formulate guidelines, so that once regimens and dosages are identified, translation into clinical studies and clinical practice can be rapid. The development of child-friendly drug formulations would need to be carried out in parallel so that pharmacokinetic studies can be undertaken as formulations are created. Significant research and development would be required and a wide range of stakeholders would need to be engaged. The time is right to consider a more thoughtful and systematic approach toward identifying, testing, and comparing combinations of drugs for children with tuberculosis.

In Vivo Bioluminescent Monitoring of Therapeutic Efficacy and Pharmacodynamic Target Assessment of Antofloxacin against Escherichia coli in a Neutropenic Murine Thigh Infection Model

Antimicrobial resistance among uropathogens has increased the rates of infection-related morbidity and mortality. Antofloxacin is a novel fluoroquinolone with broad-spectrum antibacterial activity against urinary Gram-negative bacilli, such as Escherichia coli This study monitored the in vivo efficacy of antofloxacin using bioluminescent imaging and determined pharmacokinetic (PK)/pharmacodynamic (PD) targets against E. coli isolates in a neutropenic murine thigh infection model. The PK properties were determined after subcutaneous administration of antofloxacin at 2.5, 10, 40, and 160 mg/kg of body weight. Following thigh infection, the mice were treated with 2-fold-increasing doses of antofloxacin from 2.5 to 80 mg/kg administered every 12 h. Efficacy was assessed by quantitative determination of the bacterial burdens in thigh homogenates and was compared with the bioluminescent density. Antofloxacin demonstrated both static and killing endpoints in relation to the initial burden against all study strains. The PK/PD index area under the concentration-time curve (AUC)/MIC correlated well with efficacy (R² = 0.92), and the dose-response relationship was relatively steep, as observed with escalating doses of antofloxacin. The mean free drug AUC/MIC targets necessary to produce net bacterial stasis and 1-log₁₀ and 2-log₁₀ kill for each isolate were 38.7, 66.1, and 147.0 h, respectively. In vivo bioluminescent imaging showed a rapid decrease in the bioluminescent density at free drug AUC/MIC exposures that exceeded the stasis targets. The integration of these PD targets combined with the results of PK studies with humans will be useful in setting optimal dosing regimens for the treatment of urinary tract infections due to E. coli.

En Route towards European Clinical Breakpoints for Veterinary Antimicrobial Susceptibility Testing: A Position Paper Explaining the VetCAST Approach

VetCAST is the EUCAST sub-committee for Veterinary Antimicrobial Susceptibility Testing. Its remit is to define clinical breakpoints (CBPs) for antimicrobial drugs (AMDs) used in veterinary medicine in Europe. This position paper outlines the procedures and reviews scientific options to solve challenges for the determination of specific CBPs for animal species, drug substances and disease conditions. VetCAST will adopt EUCAST approaches: the initial step will be data assessment; then procedures for decisions on the CBP; and finally the release of recommendations for CBP implementation. The principal challenges anticipated by VetCAST are those associated with the differing modalities of AMD administration, including mass medication, specific long-acting product formulations or local administration. Specific challenges comprise mastitis treatment in dairy cattle, the range of species and within species breed considerations and several other variable factors not relevant to human medicine. Each CBP will be based on consideration of: (i) an epidemiological cut-off value (ECOFF) - the highest MIC that defines the upper end of the wild-type MIC distribution; (ii) a PK/PD breakpoint obtained from pre-clinical pharmacokinetic data [this PK/PD break-point is the highest possible MIC for which a given percentage of animals in the target population achieves a critical value for the selected PK/PD index (fAUC/MIC or fT > MIC)] and (iii) when possible, a clinical cut-off, that is the relationship between MIC and clinical cure. For the latter, VetCAST acknowledges the paucity of such data in veterinary medicine. When a CBP cannot be established, VetCAST will recommend use of ECOFF as surrogate. For decision steps, VetCAST will follow EUCAST procedures involving transparency, consensus and independence. VetCAST will ensure freely available dissemination of information, concerning standards, guidelines, ECOFF, PK/PD breakpoints, CBPs and other relevant information for AST implementation. Finally, after establishing a CBP, VetCAST will promulgate expert comments and/or recommendations associated with CBPs to facilitate their sound implementation in a clinical setting.

Use of Monte Carlo simulation and considerations for PK-PD targets to support antibacterial dose selection

Monte Carlo simulation is used to generate data for pharmacokinetic-pharmacodynamic (PK-PD) target attainment analyses to assess antibacterial dosing regimens in early and late stage drug development. Careful consideration of the quality of data for pharmacokinetics, non-clinical PK-PD targets for efficacy, the choice of the bacterial reduction endpoint upon which the PK-PD target is based, variability in the PK-PD target, and effect site exposures ensures optimal dose selection. Relationships between drug exposure and efficacy and/or safety endpoints based on clinical data can also be applied to simulated data to support dose selection. These in silico analyses, conducted throughout drug development, provide the greatest opportunity to de-risk the development of antibacterial agents.

Amplification of Antimicrobial Resistance in Gut Flora of Patients Treated with Ceftriaxone

Although antibacterial therapy has an impact on human intestinal flora and the emergence of resistant bacteria, its role in the amplification of antimicrobial resistance and the quantitative exposure-effect relationship is not clear. An observational prospective study was conducted to determine whether and how ceftriaxone exposure is related to amplification of resistance in non-intensive care unit (non-ICU) patients. Serial stool samples from 122 extended-spectrum β-lactamase-positive (ESBL⁺) hospitalized patients were analyzed by quantitative real-time PCR to quantify the resistant gene bla_CTX-M Drug exposure was calculated for each patient by using a population pharmacokinetic model. Multi- and univariate regression and classification regression tree (CART) analyses were used to explore relationships between measures of exposure and amplification of bla_CTX-M genes. Amplification of bla_CTX-M was observed in 0% (0/11) of patients with no treatment and 33% (20/61) of patients treated with ceftriaxone. Stepwise regression analysis showed a significant association between amplification of bla_CTX-M and the plasma area under the concentration-time curve from 0 to 24 h for the unbound fraction of the drug (fAUC_0-24), the maximum concentration of drug in serum for the unbound fraction of the drug (fC_max), and the duration of ceftriaxone therapy. Using CART analysis, amplification of bla_CTX-M was observed in 11/16 (69%) patients treated for >14 days and in 9/40 (23%) patients treated for ≤14 days (P = 0.0019). In the latter group, amplification was observed in 5/7 (71%) patients with an fAUC_0-24 of ≥222 mg · h/liter and in 4/33 (12%) patients with lower drug exposures (P = 0.0033). A similar association was found for an fC_max of ≥30 mg/liter (63% versus 13%, P = 0.0079). A significant association was found between the amplification of bla_CTX-M resistance genes and exposure to ceftriaxone. Both duration of treatment and degree of ceftriaxone exposure have a significant impact on the amplification of resistance genes. (The project described in this paper has been registered at ClinicalTrials.gov under identifier NCT01208519.).

Clinical pharmacokinetics and pharmacodynamic target attainment of pazufloxacin in prostate tissue: Dosing considerations for prostatitis

The present study examined the clinical pharmacokinetics of pazufloxacin in prostate tissue and estimated the probability of target attainment for tissue-specific pharmacodynamic goals related to treating prostatitis using various intravenous dosing regimens. Patients with prostatic hypertrophy received prophylactic infusions of pazufloxacin (500 mg, n = 23; 1000 mg, n = 25) for 0.5 h prior to transurethral prostate resection. Drug concentrations in plasma (0.5-5 h) and prostate tissue (0.5-1.5 h) were measured by high-performance liquid chromatography and used for subsequent noncompartmental and three-compartmental analysis. Monte Carlo simulation was performed to evaluate the probability of target attainment of a specific minimum inhibitory concentration (MIC) in prostate tissue: the proportion that achieved both area under the drug concentration over time curve (AUC)/MIC = 100 and maximum concentration (C_max)/MIC = 8. Prostatic penetration of pazufloxacin was good with mean C_max ratios (prostate tissue/plasma) of 0.82-0.99 and for AUC, 0.80-0.98. The probability of reaching target MIC concentrations in prostate tissue was more than 90% for dosing schedules of 0.25 mg/L for 500 mg every 24 h (500 mg daily), 0.5 mg/L for 500 mg every 12 h (1000 mg daily), 1 mg/L for 1000 mg every 24 h (1000 mg daily), and 2 mg/L for 1000 mg every 12 h (2000 mg daily). Importantly, the 2000 mg daily regimen of pazufloxacin produced a profile sufficient to have an antibacterial effect in prostate tissue against clinical isolates of Escherichia coli and Klebsiella pneumonia with MIC values less than 2 mg/L.

Acute myeloid leukemia and the infectious diseases consultant

Infectious complications following treatment of acute myeloid leukemia (AML) are important causes of morbidity and mortality. The spectrum and complexity of these infections is reflected by the severe net state of immunosuppression of AML patients, that is dynamic and continuously changing, the polypharmacy, including the widespread use of anti-infectives and the complex epidemiology of severe and frequently resistant pathogens afflicting these patients. Infectious diseases (ID) consultants having a critical mass of expertise and intimate knowledge of the intricacies of leukemia care, add considerable value in improving outcomes of patients with AML who develop infections. Furthermore, pharmaco-economic considerations such as length of stay, choice of cost-effective anti-infective program, infection control and antibiotic stewardship strategies create a delicate interplay of the ID consultant and the ecosystem of care of AML patients. This is an increasingly recognized area of cross collaboration and a productive direction for future collaborative practice models and research.

Ghost probiotics with a combined regimen: a novel therapeutic approach against the Zika virus, an emerging world threat

The Zika virus (ZIKV) used to be an obscure flavivirus closely related to dengue virus (DENV). Transmission of this epidemic pathogen occurs mainly via mosquitoes, but it is also capable of placental and sexual transmission. Although the characteristics of these viruses are well defined, infections are unpredictable in terms of disease severity, unusual clinical manifestations, unexpected methods of transmission, long-term persistence, and the development of new strains. Recently, ZIKV has gained huge medical attention following the large-scale epidemics around the world, and reported cases of congenital abnormalities associated with Zika virus infections which have created a public health emergency of international concern. Despite continuous research on ZIKV, no specific treatment or vaccine has been developed, excepting a preventive strategy for congenital ZIKV infection. Probiotics, known as GRAS, are bacteria that confer various health beneficial effects, and have been shown to be effective at curing a number of viral diseases by modulating the immune system. Furthermore, probiotic preparations consisting of dead cells and cellular metabolites, so-called "Ghost probiotics", can also act as biological response modifiers. Here, we review available information on the epidemiology, transmission, and clinical features of ZIKV, and on treatment and prevention strategies. In addition, we emphasize the use of probiotics and plant-based natural remedies and describe their action mechanisms, and the green technologies for microbial conversion, which could contribute to the development of novel therapies that may reduce the pathogenicity of ZIKV. Accordingly, we draw attention to new findings, unanswered questions, unresolved issues, and controversies regarding ZIKV.

Phagocytes, Antibiotics, and Self-Limiting Bacterial Infections

Most antibiotic use in humans is to reduce the magnitude and term of morbidity of acute, community-acquired infections in immune competent patients, rather than to save lives. Thanks to phagocytic leucocytes and other host defenses, the vast majority of these infections are self-limiting. Nevertheless, there has been a negligible amount of consideration of the contribution of phagocytosis and other host defenses in the research for, and the design of, antibiotic treatment regimens, which hyper-emphasizes antibiotics as if they were the sole mechanism responsible for the clearance of infections. Here, we critically review this approach and its limitations. With the aid of a heuristic mathematical model, we postulate that if the rate of phagocytosis is great enough, for acute, normally self-limiting infections, then (i) antibiotics with different pharmacodynamic properties would be similarly effective, (ii) low doses of antibiotics can be as effective as high doses, and (iii) neither phenotypic nor inherited antibiotic resistance generated during therapy are likely to lead to treatment failure.

Delayed Second Dose Antibiotics for Patients Admitted From the Emergency Department With Sepsis: Prevalence, Risk Factors, and Outcomes

OBJECTIVE

1) Determine frequency and magnitude of delays in second antibiotic administration among patients admitted with sepsis; 2) Identify risk factors for these delays; and 3) Exploratory: determine association between delays and patient-centered outcomes (mortality and mechanical ventilation after second dose).

DESIGN

Retrospective, consecutive sample sepsis cohort over 10 months.

SETTING

Single, tertiary, academic medical center.

PATIENTS

All patients admitted from the emergency department with sepsis or septic shock (defined: infection, ≥ 2 systemic inflammatory response syndrome criteria, hypoperfusion/organ dysfunction) identified by a prospective quality initiative.

EXCLUSIONS

less than 18 years old, not receiving initial antibiotics in the emergency department, death before antibiotic redosing, and patient refusing antibiotics.

INTERVENTIONS

We determined first-to-second antibiotic time and delay frequency. We considered delay major for first-to-second dose time greater than or equal to 25% of the recommended interval. Factors of interest were demographics, recommended interval length, comorbidities, clinical presentation, location at second dose, initial resuscitative care, and antimicrobial activity mechanism.

MEASUREMENTS AND MAIN RESULTS

Of 828 sepsis cases, 272 (33%) had delay greater than or equal to 25%. Delay frequency increased dose dependently with shorter recommended interval: 11 (4%) delays for 24-hour intervals (median time, 18.52 hr); 31 (26%) for 12-hour intervals (median, 10.58 hr); 117 (47%) for 8-hour intervals (median, 9.60 hr); and 113 (72%) for 6-hour intervals (median, 9.55 hr). In multivariable regression, interval length significantly predicted major delay (12 hr: odds ratio, 6.98; CI, 2.33-20.89; 8 hr: odds ratio, 23.70; CI, 8.13-69.11; 6 hr: odds ratio, 71.95; CI, 25.13-206.0). Additional independent risk factors were inpatient boarding in the emergency department (odds ratio, 2.67; CI, 1.74-4.09), initial 3-hour sepsis bundle compliance (odds ratio, 1.57; CI, 1.07-2.30), and older age (odds ratio, 1.16 per 10 yr, CI, 1.01-1.34). In the exploratory multivariable analysis, major delay was associated with increased hospital mortality (odds ratio, 1.61; CI, 1.01-2.57) and mechanical ventilation (odds ratio, 2.44; CI, 1.27-4.69).

CONCLUSIONS

Major second dose delays were common, especially for patients given shorter half-life pharmacotherapies and who boarded in the emergency department. They were paradoxically more frequent for patients receiving compliant initial care. We observed association between major second dose delay and increased mortality, length of stay, and mechanical ventilation requirement.

Advanced Methods for Dose and Regimen Finding During Drug Development: Summary of the EMA/EFPIA Workshop on Dose Finding (London 4-5 December 2014)

Inadequate dose selection for confirmatory trials is currently still one of the most challenging issues in drug development, as illustrated by high rates of late‐stage attritions in clinical development and postmarketing commitments required by regulatory institutions. In an effort to shift the current paradigm in dose and regimen selection and highlight the availability and usefulness of well‐established and regulatory‐acceptable methods, the European Medicines Agency (EMA) in collaboration with the European Federation of Pharmaceutical Industries Association (EFPIA) hosted a multistakeholder workshop on dose finding (London 4–5 December 2014). Some methodologies that could constitute a toolkit for drug developers and regulators were presented. These methods are described in the present report: they include five advanced methods for data analysis (empirical regression models, pharmacometrics models, quantitative systems pharmacology models, MCP‐Mod, and model averaging) and three methods for study design optimization (Fisher information matrix (FIM)‐based methods, clinical trial simulations, and adaptive studies). Pairwise comparisons were also discussed during the workshop; however, mostly for historical reasons. This paper discusses the added value and limitations of these methods as well as challenges for their implementation. Some applications in different therapeutic areas are also summarized, in line with the discussions at the workshop. There was agreement at the workshop on the fact that selection of dose for phase III is an estimation problem and should not be addressed via hypothesis testing. Dose selection for phase III trials should be informed by well‐designed dose‐finding studies; however, the specific choice of method(s) will depend on several aspects and it is not possible to recommend a generalized decision tree. There are many valuable methods available, the methods are not mutually exclusive, and they should be used in conjunction to ensure a scientifically rigorous understanding of the dosing rationale.

White Paper: Developing Antimicrobial Drugs for Resistant Pathogens, Narrow-Spectrum Indications, and Unmet Needs

Despite progress in antimicrobial drug development, a critical need persists for new, feasible pathways to develop antibacterial agents to treat people infected with drug-resistant bacteria. Infections due to resistant gram-negative bacilli continue to cause unacceptable morbidity and mortality rates. Antibacterial agents have been historically studied in noninferiority clinical trials that focus on a single site of infection (eg, complicated urinary tract infections, intra-abdominal infections), yet these designs may not be optimal, and often are not feasible, for study of infections caused by drug-resistant bacteria. Over the past several years, multiple stakeholders have worked to develop consensus regarding paths forward with a goal of facilitating timely conduct of antimicrobial development. Here we advocate for a novel and pragmatic approach and, toward this end, present feasible trial designs for antibacterial agents that could enable conduct of narrow-spectrum, organism-specific clinical trials and ultimately approval of critically needed new antibacterial agents.

High-Performance Liquid Chromatography Method for Rich Pharmacokinetic Sampling Schemes in Translational Rat Toxicity Models With Vancomycin

A translational need exists to understand and predict vancomycin‐induced kidney toxicity. We describe: (i) a vancomycin high‐performance liquid chromatography (HPLC) method for rat plasma and kidney tissue homogenate; (ii) a rat pharmacokinetic (PK) study to demonstrate utility; and (iii) a catheter retention study to enable future preclinical studies. Rat plasma and pup kidney tissue homogenate were analyzed via HPLC for vancomycin concentrations ranging from 3–75 and 15.1–75.5 μg/mL, respectively, using a Kinetex Biphenyl column and gradient elution of water with 0.1% formic acid: acetonitrile (70:30 v/v). Sprague‐Dawley rats (n = 10) receiving 150 mg/kg of vancomycin intraperitoneally had plasma sampled for PK. Finally, a catheter retention study was performed on polyurethane catheters to assess adsorption. Precision was <6.1% for all intra‐assay and interassay HPLC measurements, with >96.3% analyte recovery. A two‐compartment model fit the data well, facilitating PK exposure estimates. Finally, vancomycin was heterogeneously retained by polyurethane catheters.

Progress in the Fight Against Multidrug-Resistant Bacteria 2005-2016: Modern Noninferiority Trial Designs Enable Antibiotic Development in Advance of Epidemic Bacterial Resistance

From a public health perspective, new antibacterial agents should be evaluated and approved for use before widespread resistance to existing agents emerges. However, for multidrug-resistant pathogens, demonstration of superior efficacy of a new agent over a current standard-of-care agent is routinely feasible only when epidemic spread of these dangerous organisms has already occurred. One solution to enable proactive drug development is to evaluate new antibiotics with improved in vitro activity against MDR pathogens using recently updated guidelines for active control, noninferiority trials of selected severe infections caused by more susceptible pathogens. Such trials are feasible because they enroll patients with infections due to pathogens with a "usual drug resistance" phenotype that will be responsive to widely registered standard-of-care comparator antibiotics. Such anticipatory drug development has constructively reshaped the antibiotic pipeline and offers the best chance of making safe and efficacious antibiotics available to the public ahead of epidemic resistance.

Dosing of caspofungin based on a pharmacokinetic/pharmacodynamic index for the treatment of invasive fungal infections in critically ill patients on continuous venovenous haemodiafiltration

INTRODUCTION

The study objective was to evaluate the efficacy of different dosages of caspofungin in the treatment of invasive candidiasis and aspergillosis, in relation to the probability of pharmacokinetic/pharmacodynamic (PK/PD) target attainment, using modelling and Monte Carlo simulations in critically ill adult patients on continuous haemodiafiltration.

METHODS

Critically ill adult patients on continuous venovenous haemodiafiltration treated with caspofungin were analysed. A population PK model was developed. Four caspofungin dosing regimens were simulated: the licensed regimen, 70 mg/day, 100 mg/day or 200 mg/day. A PK/PD target was defined as the ratio between the area under the caspofungin concentration-time curve over 24 hours and the minimal inhibitory concentration (AUC/MIC) for candidiasis or the minimal effective concentrations (AUC/MEC) for Aspergillus spp. Target attainment based on preclinical target for Candida and Aspergillus was assessed for different MIC or MEC, respectively.

RESULTS

Concentration-time data were described by a two-compartment model. Body-weight and protein concentration were the only covariates identified by the model. Goodness-of-fit plots and bootstrap analysis proved the model had a satisfactory performance. As expected, a higher maintenance dose resulted in a higher exposure. Target attainment was >90% for candidiasis (MIC≤0.06 mg/L) and aspergillosis (MEC≤0.5 mg/L), irrespective of the dosing regimen, but not for C. parapsilosis. Standard regimen was insufficient to reach the target for C. albicans and C. parapsilosis with MIC≥0.1 mg/L.

CONCLUSION

The licensed regimen of caspofungin is insufficient to achieve the PK/PD targets in critically ill patients on haemodiafiltration. The determination of MICs will enable dose scheme selection.

Pharmacokinetics and Dialytic Clearance of Ceftazidime-Avibactam in a Critically Ill Patient on Continuous Venovenous Hemofiltration

Ceftazidime-avibactam administered at 1.25 g every 8 h was used to treat multidrug-resistant Pseudomonas aeruginosa bacteremia in a critically ill patient on continuous venovenous hemofiltration (CVVH). Prefiltration plasma drug concentrations of ceftazidime and avibactam were measured at 0, 1, 2, 4, 6, and 8 h along with postfiltration and ultrafiltrate concentrations at h 2 and h 6. Plasma pharmacokinetic parameters of ceftazidime and avibactam, respectively, were as follows: maximum plasma concentration (C_max), 61.10 and 14.54 mg/liter; minimum plasma concentration (C_min), 31.96 and 8.45 mg/liter; half-life (t_1/2), 6.07 and 6.78 h; apparent volume of distribution at the steady state (V_ss), 27.23 and 30.81 liters; total clearance at the steady state (CL_ss), 2.87 and 2.95 liters/h; area under the concentration-time curve from 0 to 8 h (AUC_0-8), 347.87 and 85.69 mg · h/liter. Concentrations of ceftazidime in plasma exceeded the ceftazidime-avibactam MIC (6 mg/liter) throughout the 8-h dosing interval. Mean CVVH extraction ratios for ceftazidime and avibactam were 14.44% and 11.53%, respectively, and mean sieving coefficients were 0.96 and 0.93, respectively. The calculated mean clearance of ceftazidime by CVVH was 1.64 liters/h and for avibactam was 1.59 liters/h, representing 57.1% of the total clearance of ceftazidime and 54.3% of the total clearance of avibactam. Further data that include multiple patients and dialysis modes are needed to verify the optimal ceftazidime-avibactam dosing strategy during critical illness and CVVH.

Oral Bioavailability and Plasma Disposition of Pefloxacin in Healthy Broiler Chickens

The pharmacokinetics of pefloxacin after single 10 mg/kg BW intravenous (IV) and oral doses were studied in healthy broiler chickens. For 24 h, serial blood samples were obtained after IV and oral administration. Concentrations of pefloxacin and its major metabolite N-demethyl pefloxacin (norfloxacin) were measured by use of high-performance liquid chromatography. The plasma concentrations–time data were found to fit a two-compartment open model. For pefloxacin, the elimination half-life (t_½β) was 8.44 ± 0.48 and 13.18 ± 0.82 h after IV and oral administration, respectively. After single oral dose, pefloxacin was rapidly absorbed with an absorption half-life (t_½a) and T_MAX of 0.87 ± 0.07 and 2.01 ± 0.12 h, respectively. Maximum plasma concentration (C_MAX) was 4.02 ± 0.31 µg/mL. Oral bioavailability of pefloxacin was found to be 70 ± 2%. Pefloxacin was converted to N-demethyl pefloxacin (norfloxacin). This metabolite represented 5% of the parent drug plasma concentrations. The maximal plasma concentration (C_MAX) of N-demethyl pefloxacin (norfloxacin) was calculated as 0.19 ± 0.01 mg/mL. The t_½β of N-demethyl pefloxacin after oral pefloxacin administration was 10.93 ± 0.80 h. The results indicate that an oral dose of 10 mg pefloxacin/kg BW, every 24 h, should be effective in treatment of the most systemic infections in poultry.

Effect of the 2014 Clinical and Laboratory Standards Institute urine-specific breakpoints on cefazolin susceptibility rates at a community teaching hospital

Background

Enterobacteriaceae, which include Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, are identified as the infectious etiology in the majority of urinary tract infections (UTIs) in community hospitals across the United States. The minimum inhibitory concentration (MIC) is a useful tool when choosing an appropriate antibacterial agent. Recent changes to the 2014 Clinical and Laboratory Standards Institute (CLSI) guidelines included reporting a urine-specific cefazolin breakpoint for enterobacteriaceae (susceptible ≤16 mcg/mL). The purpose of this study was to determine the clinical and financial impact of implementing the 2014 CLSI urine-specific breakpoints for cefazolin in a community-based teaching hospital in the Southern U.S.A.

Methods

A retrospective review of patients hospitalized from January 1, 2010 through October 1, 2014 was performed. Patients that met inclusion criteria had a documented initial clinical isolate of E. coli, K. pneumoniae, or P. mirabilis from urine cultures during each year. Descriptive statistics and two-proportion test of hypothesis were used in the analysis to compare susceptibility rates before and after implementation of the updated CLSI breakpoints for cefazolin.

Results

A total of 190 clinical isolates from patients were included in the study. E. coli was the most common organism isolated (63.7%), followed by K. pneumoniae (22.1%), and P. mirabilis (14.2%). 86% of the included isolates were susceptible to cefazolin using the 2010 breakpoints. Implementation of the 2014 breakpoints did not significantly impact susceptibility results for E. coli, K. pneumoniae, or P. mirabilis.

Conclusion

Modification of breakpoints did not significantly impact susceptibility rates of cefazolin. Substituting cefazolin may decrease the overall drug cost by 77.5%. More data is needed to correlate in vitro findings with clinical outcomes using cefazolin for UTIs.

Correcting a Fundamental Flaw in the Paradigm for Antimicrobial Susceptibility Testing

The emergence and prevalence of antibiotic-resistant bacteria are an increasing cause of death worldwide, resulting in a global ‘call to action’ to avoid receding into an era lacking effective antibiotics. Despite the urgency, the healthcare industry still relies on a single in vitro bioassay to determine antibiotic efficacy. This assay fails to incorporate environmental factors normally present during host-pathogen interactions in vivo that significantly impact antibiotic efficacy. Here we report that standard antimicrobial susceptibility testing (AST) failed to detect antibiotics that are in fact effective in vivo; and frequently identified antibiotics that were instead ineffective as further confirmed in mouse models of infection and sepsis. Notably, AST performed in media mimicking host environments succeeded in identifying specific antibiotics that were effective in bacterial clearance and host survival, even though these same antibiotics failed in results using standard test media. Similarly, our revised media further identified antibiotics that were ineffective in vivo despite passing the AST standard for clinical use. Supplementation of AST medium with sodium bicarbonate, an abundant in vivo molecule that stimulates global changes in bacterial structure and gene expression, was found to be an important factor improving the predictive value of AST in the assignment of appropriate therapy. These findings have the potential to improve the means by which antibiotics are developed, tested, and prescribed.

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Standard antimicrobial susceptibility testing (AST) is fundamentally flawed because it is based largely on in vitro efficacy.

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AST performed under conditions that mimic natural infections improves the assignment of appropriate antibiotic therapy.

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In vivo altered susceptibility (IVAS) provides a new paradigm for drug discovery and therapeutic intervention.

Drug testing often excludes potent antibiotics for the treatment of bacterial infections, while frequently identifying antibiotics that are ineffective. However, drug testing under conditions that mimic natural infections succeeded in identifying effective antibiotics, even though these same antibiotics failed standard tests. This work suggests that standard drug-testing may be hindering patient treatment and slowing the process of discovery of new, effective, and safe antibiotics because it disqualifies effective compounds. These findings call for an overhaul of standardized drug testing which hasn't changed in > 50 years.

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

Fosfomycin is a broad-spectrum agent with activity against Gram-positive and Gram-negative bacteria, including drug-resistant strains, such as extended-spectrum-beta-lactamase (ESBL)-producing and carbapenem-resistant (CR) Gram-negative rods. In the present study, the pharmacokinetic/pharmacodynamic (PK/PD) activity of ZTI-01 (fosfomycin for injection) was evaluated in the neutropenic murine thigh infection model against 5 Escherichia coli, 3 Klebsiella pneumoniae, and 2 Pseudomonas aeruginosa strains, including a subset with ESBL and CR phenotypes. The pharmacokinetics of ZTI-01 were examined in mice after subcutaneous administration of 3.125, 12.5, 50, 200, 400, and 800 mg/kg of body weight. The half-life ranged from 0.51 to 1.1 h, area under the concentration-time curve (AUC_0-∞) ranged from 1.4 to 87 mg · h/liter, and maximum concentrations ranged from 0.6 to 42.4 mg/liter. Dose fractionation demonstrated the AUC/MIC ratio to be the PK/PD index most closely linked to efficacy (R² = 0.70). Net stasis and bactericidal activity were observed against all strains. Net stasis was observed at 24-h AUC/MIC ratio values of 24, 21, and 15 for E. coli, K., pneumoniae and P. aeruginosa, respectively. For the Enterobacteriaceae group, stasis was noted at mean 24-h AUC/MIC ratio targets of 23 and 1-log kill at 83. Survival in mice infected with E. coli 145 was maximal at 24-h AUC/MIC ratio exposures of 9 to 43, which is comparable to the stasis exposures identified in the PK/PD studies. These results should prove useful for the design of clinical dosing regimens for ZTI-01 in the treatment of serious infections due to Enterobacteriaceae and Pseudomonas.

PK-PD Compass: bringing infectious diseases pharmacometrics to the patient's bedside

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.

Efficacy of tedizolid against methicillin-resistant Staphylococcus aureus and Peptostreptococcus anaerobius in thigh mixed-infection mouse model

OBJECTIVE

The purpose of this study is to compare the antimicrobial activity of human simulated exposures of tedizolid 200 mg daily, and linezolid 600 mg every 12 h for the treatment of complicated skin and skin structure infection (cSSSI) caused by MRSA and Peptostreptococcus anaerobius in both the neutropenic mice thigh mixed-infection models.

MATERIAL AND METHOD

Tedizolid phosphate and linezolid were used for all in vivo testing. A total of one MRSA and two P. anaerobius isolates were utilized. Antimicrobial efficacy was calculated for each isolate as the change in bacterial numbers (Δlog₁₀ CFU/ml) obtained in the treated mice after 24 h compared with the numbers in the starting control animals (0 h).

RESULTS

The tedizolid and linezolid MICs for MRSA was 0.25 and 2 μg/ml. Tedizolid MIC for P. anaerobius was 0.12 μg/ml, and linezolid MICs for two P. anaerobius isolates were 0.5 and 1 μg/ml. In mixed infection model, tedizolid therapy showed similar antimicrobial activities for one MRSA and two P. anaerobius isolates evaluated, compared with linezolid therapy. Additionally, when comparing the activity of tedizolid and linezolid monotherapy between single infection and mixed infection model, antimicrobial activities of both antimicrobials were attenuated when mixed infection model was used.

CONCLUSION

In the neutropenic murine thigh infection model, human simulated exposures of tedizolid and linezolid resulted in similar efficacies against MRSA, even though single and mixed infection models were used. These data support the clinical utility of tedizolid for use against MRSA and P. anaerobius in the treatment of cSSSI.

Analysis of positions and substituents on genotoxicity of fluoroquinolones with quantitative structure-activity relationship and 3D Pharmacophore model

The genotoxicity values of 21 quinolones were studied to establish a quantitative structure-activity relationship model and 3D Pharmacophore model separately for screening essential positions and substituents that contribute to genotoxicity of fluoroquinolones (FQs). A full factor experimental design was performed to analyze the specific main effect and second-order interaction effect of different positions and substituents on genotoxicity, forming a reasonable modification scheme which was validated on typical FQ with genotoxicity and efficacy data. Four positions (1, 5, 7, 8) were screened finally to form the full factorial experimental design which contained 72 congeners in total, illustrating that: the dominant effect of 5 and 7-positions on genotoxicity of FQs is main effect; meanwhile the effect of 1 and 8-positions is a second-order interaction effect; two adjacent positions always have stronger second-order interaction effect and lower genotoxicity; the obtained modification scheme had been validated on typical FQ congeners with the modified compound has a lower genotoxicity, higher synthesis feasibilities and efficacy.

Pharmacokinetic-Pharmacodynamic Evaluation of Gepotidacin against Gram-Positive Organisms Using Data from Murine Infection Models

Gepotidacin (formerly called GSK2140944) is a novel triazaacenaphthylene bacterial topoisomerase inhibitor with in vitro activity against conventional and biothreat pathogens, including Staphylococcus aureus and Streptococcus pneumoniae Using neutropenic murine thigh and lung infection models, the pharmacokinetics-pharmacodynamics (PK-PD) of gepotidacin against S. aureus and S. pneumoniae were characterized. Candidate models were fit to single-dose PK data from uninfected mice (for doses of 16 to 128 mg/kg of body weight given subcutaneously [s.c.]). Dose fractionation studies (1 isolate/organism; 2 to 512 mg/kg/day) and dose-ranging studies (5 isolates/organism; 2 to 2,048 mg/kg/day; MIC ranges of 0.5 to 2 mg/liter for S. aureus and 0.125 to 1 mg/liter for S. pneumoniae) were conducted. The presence of an in vivo postantibiotic effect (PAE) was also evaluated. Relationships between the change from baseline in log₁₀ CFU at 24 h and the ratio of the free-drug plasma area under the concentration-time curve (AUC) to the MIC (AUC/MIC ratio), the ratio of the maximum concentration of drug in plasma (C_max) to the MIC (C_max/MIC ratio), and the percentage of a 24-h period that the drug concentration exceeded the MIC (%T>MIC) were evaluated using Hill-type models. Plasma and epithelial lining fluid (ELF) PK data were best fit by a four-compartment model with linear distributional clearances, a capacity-limited clearance, and a first-order absorption rate. The ELF penetration ratio in uninfected mice was 0.65. Since the growth of both organisms was poor in the murine lung infection model, lung efficacy data were not reported. As determined using the murine thigh infection model, the free-drug plasma AUC/MIC ratio was the PK-PD index most closely associated with efficacy (r² = 0.936 and 0.897 for S. aureus and S. pneumoniae, respectively). Median free-drug plasma AUC/MIC ratios of 13.4 and 58.9 for S. aureus, and 7.86 and 16.9 for S. pneumoniae, were associated with net bacterial stasis and a 1-log₁₀ CFU reduction from baseline, respectively. Dose-independent PAE durations of 3.07 to 12.5 h and 5.25 to 8.46 h were demonstrated for S. aureus and S. pneumoniae, respectively.

A Robust Pneumonia Model in Immunocompetent Rodents to Evaluate Antibacterial Efficacy against S. pneumoniae, H. influenzae, K. pneumoniae, P. aeruginosa or A. baumannii

Efficacy of candidate antibacterial treatments must be demonstrated in animal models of infection as part of the discovery and development process, preferably in models which mimic the intended clinical indication. A method for inducing robust lung infections in immunocompetent rats and mice is described which allows for the assessment of treatments in a model of serious pneumonia caused by S. pneumoniae, H. influenzae, P. aeruginosa, K. pneumoniae or A. baumannii. Animals are anesthetized, and an agar-based inoculum is deposited deep into the lung via nonsurgical intratracheal intubation. The resulting infection is consistent, reproducible, and stable for at least 48 h and up to 96 h for most isolates. Studies with marketed antibacterials have demonstrated good correlation between in vivo efficacy and in vitro susceptibility, and concordance between pharmacokinetic/pharmacodynamic targets determined in this model and clinically accepted targets has been observed. Although there is an initial time investment when learning the technique, it can be performed quickly and efficiently once proficiency is achieved. Benefits of the model include elimination of the neutropenic requirement, increased robustness and reproducibility, ability to study more pathogens and isolates, improved flexibility in study design and establishment of a challenging infection in an immunocompetent host.

Population Pharmacokinetics and Target Attainment of Ertapenem in Plasma and Tissue Assessed via Microdialysis in Morbidly Obese Patients after Laparoscopic Visceral Surgery

Ertapenem provides broad-spectrum activity against many pathogens, and its use is relevant for the prophylaxis and treatment of infections in morbidly obese patients undergoing surgery. However, its pharmacokinetics and tissue penetration in these patients are not well defined. We assessed the population pharmacokinetics and target attainment for ertapenem in the plasma, subcutaneous tissue, and peritoneal fluid of morbidly obese patients. Six female patients (body mass index, 43.7 to 55.9 kg/m²) received 1,000 mg ertapenem as 15-min infusions at 0 and 26 h. On day 2, the unbound ertapenem concentrations in plasma, subcutaneous tissue, and peritoneal fluid were measured by microdialysis; total plasma concentrations were additionally quantified. The probability of attaining a target of an unbound ertapenem concentration above the MIC for at least 40% of the dosing interval was predicted via Monte Carlo simulations. The population pharmacokinetic model contained two disposition compartments and simultaneously described all concentrations. For unbound ertapenem, total clearance was 12.3 liters/h (coefficient of variation, 21.6% for between-patient variability) and the volume of distribution at steady state was 57.8 liters in patients with a 53-kg fat-free mass. The area under the concentration-time curve (AUC) for ertapenem was 49% lower in subcutaneous tissue and 25% lower in peritoneal fluid than the unbound AUC in plasma. Tissue penetration was rapid (equilibration half-life, <15 min) and was variable in subcutaneous tissue. Short-term ertapenem infusions (1,000 mg every 24 h) achieved robust (>90%) target attainment probabilities for MICs of up to 1 mg/liter in plasma, 0.25 to 0.5 mg/liter in subcutaneous tissue, and 0.5 mg/liter in peritoneal fluid. Ertapenem presents an attractive choice for many pathogens relevant to morbidly obese patients undergoing surgery. (This study has been registered at ClinicalTrials.gov under identifier NCT01407965.).

Simplifying Piperacillin/Tazobactam Dosing: Pharmacodynamics of Utilizing Only 4.5 or 3.375 g Doses for Patients With Normal and Impaired Renal Function

OBJECTIVES

To evaluate the pharmacodynamic exposure of piperacillin/tazobactam across the renal function range using 4.5 or 3.375 g dosing regimens.

METHODS

A 5000-patient Monte Carlo simulation was conducted to determine the probability of achieving 50% free time above the minimum inhibitory concentration ( fT > MIC) for piperacillin. Proposed regimens, using solely 4.5 or 3.375 g strengths, were compared with regimens listed in piperacillin/tazobactam prescribing information over creatinine clearance (CrCl) ranges of 120 mL/min to hemodialysis. The probability of target attainment (PTA) at MICs ≤ 16 μg/mL was compared between proposed and standard regimens.

RESULTS

At CrCl 41 to 120 mL/min, prolonged infusions of 4.5 g (3 hours) and 3.375 g (4 hours) every 6 hours resulted in ≥95% PTA versus ≥76% for standard regimens (0.5 hour). At CrCl 20 to 40 mL/min, 4.5 and 3.375 g every 8 hours as prolonged infusions achieved slightly higher PTA (≥98%) versus standard regimens (≥93%). Similarly, PTA achieved with prolonged infusions of 4.5 and 3.375 g every 12 hours (≥93%) was comparable with those of standard regimens (≥91%) at CrCl 1 to 19 mL/min. In hemodialysis, 100% PTA was achieved with prolonged infusion regimens.

CONCLUSION

Piperacillin/tazobactam regimens designed around the 4.5 or 3.375 g dose and prolonged infusions provided similar or better PTA at MICs ≤ 16 μg/mL compared with standard regimens. These observations may support the stocking and use of a single piperacillin/tazobactam strength to simplify dosing.

In Vitro and In Vivo Activities of a Bi-Aryl Oxazolidinone, RBx 11760, against Gram-Positive Bacteria

RBx 11760, a bi-aryl oxazolidinone, was investigated for antibacterial activity against Gram-positive bacteria. The MIC₉₀s of RBx 11760 and linezolid against Staphylococcus aureus were 2 and 4 mg/liter, against Staphylococcus epidermidis were 0.5 and 2 mg/liter, and against Enterococcus were 1 and 4 mg/liter, respectively. Similarly, against Streptococcus pneumoniae the MIC₉₀s of RBx 11760 and linezolid were 0.5 and 2 mg/liter, respectively. In time-kill studies, RBx 11760, tedizolid, and linezolid exhibited bacteriostatic effect against all tested strains except S. pneumoniae RBx 11760 showed 2-log₁₀ kill at 4× MIC while tedizolid and linezolid showed 2-log₁₀ and 1.4-log₁₀ kill at 16× MIC, respectively, against methicillin-resistant S. aureus (MRSA) H-29. Against S. pneumoniae 5051, RBx 11760 showed bactericidal activity, with 4.6-log₁₀ kill at 4× MIC compared to 2.42-log₁₀ and 1.95-log₁₀ kill for tedizolid and linezolid, respectively, at 16× MIC. RBx 11760 showed postantibiotic effects (PAE) at 3 h at 4 mg/liter against MRSA H-29, and linezolid showed the same effect at 16 mg/liter. RBx 11760 inhibited biofilm production against methicillin-resistant S. epidermidis (MRSE) ATCC 35984 in a concentration-dependent manner. In a foreign-body model, linezolid and rifampin resulted in no advantage over stasis, while the same dose of RBx 11760 demonstrated a significant killing compared to the initial control against S. aureus (P < 0.05) and MRSE (P < 0.01). The difference in killing was statistically significant for the lower dose of RBx 11760 (P < 0.05) versus the higher dose of linezolid (P > 0.05 [not significant]) in a groin abscess model. In neutropenic mouse thigh infection, RBx 11760 showed stasis at 20 mg/kg of body weight, whereas tedizolid showed the same effect at 40 mg/kg. These data support RBx 11760 as a promising investigational candidate.

Fractal Geometry-Based Decrease in Trimethoprim-Sulfamethoxazole Concentrations in Overweight and Obese People

Trimethoprim-sulfamethoxazole (TMP-SMX) is one of the most widely drugs on earth. The World Health Organization recommends it as an essential basic drug for all healthcare systems. Dosing is inconsistently based on weight, assuming linear relationships. Given that obesity is now a global "pandemic" it is vital that we evaluate the effect of obesity on trimethoprim-sulfamethoxazole concentrations. We conducted a prospective clinical experiment based on optimized design strategies and artificial intelligence algorithms and found that weight and body mass index (BMI) had a profound effect on drug clearance and volume of distribution, and followed nonlinear fractal geometry-based relationships. The findings were confirmed by demonstrating decreased TMP-SMX peak and area under the concentration-time curves in overweight patients based on standard regression statistics. The nonlinear relationships can now be used to identify new TMP-SMX doses in overweight and obese patients for each of the infections caused by the >60 pathogens for which the drug is indicated.

Animal models in the pharmacokinetic/pharmacodynamic evaluation of antimicrobial agents

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

Clinical Pharmacology of Delafloxacin in Patients With Hepatic Impairment

Delafloxacin is a novel anionic fluoroquinolone with robust activity against Gram‐positive, Gram‐negative, atypical, and anaerobic bacteria, including methicillin‐resistant S aureus. Delafloxacin is currently being studied for the treatment of acute bacterial skin and skin structure infections and community‐acquired pneumonia. This was a phase 1, open‐label pharmacokinetic and safety study of a single intravenous dose of 300 mg delafloxacin in subjects with mild, moderate, and severe hepatic impairment (Child‐Pugh class A, B, and C, respectively) compared with matched healthy controls. The effects of hepatic impairment were assessed by ANOVA of log‐transformed values for AUC_0‐∞, C_max, and systemic clearance, with hepatic group as a fixed effect. Mean AUC_0‐∞ and C_max in each impairment group were not significantly different from those of the pooled healthy subjects (P > 0.05). The 90% confidence interval (CI) of the percentage ratios of least‐squares means of AUC_0‐∞ did not indicate significant differences between the impairment groups and pooled healthy controls: Child‐Pugh class A (mild) 114.4 (CI: 95.6, 137.0), Child‐Pugh class B (moderate) 114.8 (CI: 95.9, 137.4), and Child‐Pugh class C (severe) 115.1 (CI: 96.1, 137.8). A single IV infusion of delafloxacin was generally well tolerated in all treatment groups. The exposure and clearance of delafloxacin in subjects with mild, moderate, or severe hepatic impairment did not significantly differ from those of pooled, matched healthy subjects. Based on these pharmacokinetic data, dose adjustment of delafloxacin in the presence of hepatic impairment is not needed.

Penetration of Ceftaroline into the Epithelial Lining Fluid of Healthy Adult Subjects

Ceftaroline, the active metabolite of the prodrug ceftaroline fosamil, is a cephalosporin with bactericidal activity against Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA). This study aimed to (i) evaluate ceftaroline concentrations in human plasma and epithelial lining fluid (ELF) and (ii) develop a population pharmacokinetic (PK) model for plasma and ELF to be used in PK/pharmacodynamic (PD) target attainment simulations. Ceftaroline concentrations in ELF and plasma at steady state (day 4) were measured in healthy adult subjects for two dosages: 600 mg every 12 h (q12h) and 600 mg every 8 h (q8h). Both were well tolerated with no serious adverse events. The penetration of free ceftaroline into ELF, assuming 20% protein binding in plasma and no protein binding in ELF, was ≈23%. The population PK model utilized a two-compartment model for both ceftaroline fosamil and ceftaroline. Goodness-of-fit criteria revealed the model was consistent with observed data and no systematic bias remained. At 600 mg q12h and a MIC of 1 mg/liter, 98.1% of simulated patients would be expected to achieve a target free drug concentration above the MIC (fT>MIC) in plasma of 42%, and in ELF 81.7% would be expected to achieve a target fT>MIC of 17%; at 600 mg q8h, 100% were predicted to achieve an fT>MIC in plasma of 42% and 94.7% to achieve an fT>MIC of 17% in ELF. The literature and data suggest the 600 mg q12h dose is adequate for MICs of ≤1 mg/liter. There is a need for clinical data in patients with MRSA pneumonia and data to correlate PK/PD relationships in ELF with clinical outcomes.

Multidrug-Resistant Pseudomonas aeruginosa Infection in a Child with Cystic Fibrosis

We describe a pediatric cystic fibrosis patient who developed a pulmonary exacerbation due to two multidrug-resistant (MDR) Pseudomonas aeruginosa isolates. In addition to these MDR organisms, the case was further complicated by β-lactam allergy. Despite the MDR phenotype, both isolates were susceptible to an antimicrobial combination.