Effect of dosing and dosing frequency on the efficacy of ceftizoxime and the emergence of ceftizoxime resistance during the early development of murine abscesses caused by Bacteroides fragilis and Enterobacter cloacae mixed infection

Challenges for global antibiotic regimen planning and establishing antimicrobial resistance targets: implications for the WHO Essential Medicines List and AWaRe antibiotic book dosing

SUMMARYThe World Health Organisation's 2022 AWaRe Book provides guidance for the use of 39 antibiotics to treat 35 infections in primary healthcare and hospital facilities. We review the evidence underpinning suggested dosing regimens. Few (n = 18) population pharmacokinetic studies exist for key oral AWaRe antibiotics, largely conducted in homogenous and unrepresentative populations hindering robust estimates of drug exposures. Databases of minimum inhibitory concentration distributions are limited, especially for community pathogen-antibiotic combinations. Minimum inhibitory concentration data sources are not routinely reported and lack regional diversity and community representation. Of studies defining a pharmacodynamic target for ß-lactams (n = 80), 42 (52.5%) differed from traditionally accepted 30%-50% time above minimum inhibitory concentration targets. Heterogeneity in model systems and pharmacodynamic endpoints is common, and models generally use intravenous ß-lactams. One-size-fits-all pharmacodynamic targets are used for regimen planning despite complexity in drug-pathogen-disease combinations. We present solutions to enable the development of global evidence-based antibiotic dosing guidance that provides adequate treatment in the context of the increasing prevalence of antimicrobial resistance and, moreover, minimizes the emergence of resistance.

A Randomized Clinical Trial of Bayesian-Guided Beta-Lactam Infusion Strategy and Associated Bacterial Resistance and Clinical Outcomes in Patients With Severe Pneumonia

BACKGROUND

Antimicrobial resistance is a growing health concern worldwide. The objective of this study was to evaluate the effect of beta-lactam infusion on the emergence of bacterial resistance in patients with severe pneumonia in the intensive care unit.

METHODS

Adult intensive care patients receiving cefepime, meropenem, or piperacillin-tazobactam for severe pneumonia caused by Gram-negative bacteria were randomized to receive beta-lactams as an intermittent (30 minutes) or continuous (24 hours) infusion. Respiratory samples for culture and susceptibility testing, with minimum inhibitory concentrations (MIC), were collected once a week for up to 4 weeks. Beta-lactam plasma concentrations were measured and therapeutic drug monitoring was performed using Bayesian software as the standard of care.

RESULTS

The study was terminated early owing to slow enrollment. Thirty-five patients were enrolled in this study. Cefepime (n = 22) was the most commonly prescribed drug at randomization, followed by piperacillin (n = 8) and meropenem (n = 5). Nineteen patients were randomized into the continuous infusion arm and 16 into the intermittent infusion arm. Pseudomonas aeruginosa was the most common respiratory isolate (n = 19). Eighteen patients were included in the final analyses. No differences in bacterial resistance were observed between arms ( P = 0.67). No significant differences in superinfection ( P = 1), microbiological cure ( P = 0.85), clinical cure at day 7 ( P = 0.1), clinical cure at end of therapy ( P = 0.56), mortality ( P = 1), intensive care unit length of stay ( P = 0.37), or hospital length of stay ( P = 0.83) were observed. Achieving 100% ƒT > MIC ( P = 0.04) and ƒT > 4 × MIC ( P = 0.02) increased likelihood of clinical cure at day 7 of therapy.

CONCLUSIONS

No differences in the emergence of bacterial resistance or clinical outcomes were observed between intermittent and continuous infusions. Pharmacokinetic/pharmacodynamic target attainment may be associated with a clinical cure on day 7.

Emergence of Resistance in Klebsiella aerogenes to Piperacillin-Tazobactam and Ceftriaxone

We examined the effects of piperacillin-tazobactam (TZP) concentration and bacterial inoculum on in vitro killing and the emergence of resistance in Klebsiella aerogenes The MICs for 15 clinical respiratory isolates were determined by broth microdilution for TZP and by Etest for ceftriaxone (CRO) and cefepime (FEP). The presence of resistance in TZP-susceptible isolates (n = 10) was determined by serial passes over increasing concentrations of TZP-containing and CRO-containing agar plates. Isolates with growth on TZP 16/4-μg/ml and CRO 8-μg/ml plates (n = 5) were tested in high-inoculum (HI; 7.0 log10 CFU/ml) and low-inoculum (LI; 5.0 log10 CFU/ml) time-kill studies. Antibiotic concentrations were selected to approximate TZP 3.375 g every 8 h (q8h) via a 4-h prolonged-infusion free peak concentration (40 μg/ml [TZP40]), peak epithelial lining fluid (ELF) concentrations, and average AUC0-24 values for TZP (20 μg/ml [TZP20] and 10 μg/ml [TZP10], respectively), the ELF FEP concentration (14 μg/ml), and the average AUC0-24 CRO concentration (6 μg/ml). For HI, FEP exposure significantly reduced 24-h inocula against all comparators (P ≤ 0.05) with a reduction of 4.93 ± 0.64 log10 CFU/ml. Exposure to TZP40, TZP20, and TZP10 reduced inocula by 0.81 ± 0.43, 0.21 ± 0.18, and 0.05 ± 0.16 log10 CFU/ml, respectively. CRO-exposed isolates demonstrated an increase of 0.42 ± 0.39 log10 CFU/ml compared to the starting inocula, with four of five CRO-exposed isolates demonstrating TZP-nonsusceptibility. At LI after 24 h of exposure to TZP20 and TZP10, the starting inoculum decreased by averages of 2.24 ± 1.98 and 2.91 ± 0.50 log10 CFU/ml, respectively. TZP demonstrated significant inoculum-dependent killing, warranting dose optimization studies.

What Antibiotic Exposures Are Required to Suppress the Emergence of Resistance for Gram-Negative Bacteria? A Systematic Review

BACKGROUND

The rates of antibiotic resistance in Gram-negative bacteria are increasing. One method to minimize resistance emergence may be optimization of antibiotic dosing regimens to achieve drug exposure that suppress the emergence of resistance.

OBJECTIVE

The aim of this systematic review was to describe the antibiotic exposures associated with suppression of the emergence of resistance for Gram-negative bacteria.

METHODS

We conducted a search of four electronic databases. Articles were included if the antibiotic exposure required to suppress the emergence of resistance in a Gram-negative bacterial isolate was described. Among studies, 57 preclinical studies (in vitro and in vivo) and 2 clinical studies 59 included investigated the monotherapy of antibiotics against susceptible and/or intermediate Gram-negative bacteria.

RESULTS

The pharmacokinetic/pharmacodynamic (PK/PD) indices reported to suppress the emergence of antibiotic resistance for various classes were β-lactam antibiotic minimum concentration to minimum inhibitory concentration (Cmin/MIC) ≥ 4; aminoglycoside maximum concentration to MIC (Cmax/MIC) ratio ≥ 20; fluoroquinolones, area under the concentration-time curve from 0 to 24 h to mutant prevention concentration (AUC24/MPC) ≥ 35; tetracyclines, AUC24 to MIC (AUC24/MIC) ratio ≥ 50; polymyxin B, AUC24/MIC ≥ 808; and fosfomycin, AUC24/MIC ≥ 3136. However, the exposures required to suppress the emergence of resistance varied depending on the specific antibiotic tested, the duration of the experiment, the bacterial species and the specific bacterial isolate tested. Importantly, antibiotic exposures required to suppress the emergence of resistance generally exceeded that associated with clinical efficacy.

CONCLUSION

The benefits of implementing such high PK/PD targets must be balanced with the potential risks of antibiotic-associated toxicity.

Aggressive or moderate drug therapy for infectious diseases? Trade-offs between different treatment goals at the individual and population levels

Antimicrobial resistance is one of the major public health threats of the 21st century. There is a pressing need to adopt more efficient treatment strategies in order to prevent the emergence and spread of resistant strains. The common approach is to treat patients with high drug doses, both to clear the infection quickly and to reduce the risk of de novo resistance. Recently, several studies have argued that, at least in some cases, low-dose treatments could be more suitable to reduce the within-host emergence of antimicrobial resistance. However, the choice of a drug dose may have consequences at the population level, which has received little attention so far. Here, we study the influence of the drug dose on resistance and disease management at the host and population levels. We develop a nested two-strain model and unravel trade-offs in treatment benefits between an individual and the community. We use several measures to evaluate the benefits of any dose choice. Two measures focus on the emergence of resistance, at the host level and at the population level. The other two focus on the overall treatment success: the outbreak probability and the disease burden. We find that different measures can suggest different dosing strategies. In particular, we identify situations where low doses minimize the risk of emergence of resistance at the individual level, while high or intermediate doses prove most beneficial to improve the treatment efficiency or even to reduce the risk of resistance in the population.

Infections by multidrug-resistant Gram-negative Bacteria: What's new in our arsenal and what's in the pipeline?

The spread of multidrug-resistant bacteria is an ever-growing concern, particularly among Gram-negative bacteria because of their intrinsic resistance and how quickly they acquire and spread new resistance mechanisms. Treating infections caused by Gram-negative bacteria is a challenge for medical practitioners and increases patient mortality and cost of care globally. This vulnerability, along with strategies to tackle antimicrobial resistance development, prompts the development of new antibiotic agents and exploration of alternative treatment options. This article summarises the new antibiotics that have recently been approved for Gram-negative bacterial infections, looks down the pipeline at promising agents currently in phase I, II, or III clinical trials, and introduces new alternative avenues that show potential in combating multidrug-resistant Gram-negative bacteria.

Emergence of antimicrobial resistance to piperacillin/tazobactam or meropenem in the ICU: Intermittent versus continuous infusion. A retrospective cohort study

BACKGROUND

Prolonged infusion of beta-lactam antibiotics is broadly recognized as a strategy to optimize antibiotic therapy by achieving a higher percentage of time that concentrations remain above the minimal inhibitory concentration (% fT_>MIC), i.e. the pharmacokinetic/pharmacodynamic (PK/PD) index. However, %fT_>MIC may not be the PK/PD index of choice for inhibition of resistance emergence and it is therefore unsure what impact prolonged infusion of beta-lactam antibiotics may have on the emergence of resistance.

METHODS

A retrospective cohort study including 205 patients receiving either intermittent (101 patients) or continuous (104 patients) infusion of piperacillin/tazobactam or meropenem was conducted in the ICU of the Ghent University Hospital. Logistic regression analysis was used to develop a prediction model and to determine whether the mode of infusion was a predictor of emergence of antimicrobial resistance.

RESULTS

Resistant strains emerged in 24 out of the 205 patients (11.7%). The mode of infusion was no predictor of emergence of antimicrobial resistance. Infection with Pseudomonas aeruginosa was associated with a significantly higher risk for emergence of resistance.

CONCLUSIONS

In this retrospective cohort study, the emergence of antimicrobial resistance to piperacillin/tazobactam or meropenem was not related to the mode of infusion.

Differences in suppression of regrowth and resistance despite similar initial bacterial killing for meropenem and piperacillin/tazobactam against Pseudomonas aeruginosa and Escherichia coli

We described bacterial killing and resistance emergence at various fixed concentrations of meropenem and piperacillin/tazobactam against Pseudomonas aeruginosa and Escherichia coli. Time-kill studies were conducted utilizing nine isolates and a large range of concentrations. Within each strain and antibiotic, initial killing was similar, with concentrations ≥2×MIC. At many (strain-specific) concentrations causing substantial initial killing, regrowth occurred at 24-48h. For remaining concentrations, growth typically remained suppressed (<5-log₁₀ cfu/mL). The concentrations of meropenem required to suppress regrowth ranged from 2-8×MIC for P. aeruginosa and 2-64×MIC for E. coli. For piperacillin/tazobactam, the equivalent concentrations ranged from 8-16×MIC for P. aeruginosa and 4-16×MIC for E. coli. The number of less-susceptible bacteria increased with rising concentrations before decreasing at even higher concentrations. Suppression of regrowth and resistance was substantially improved with higher concentrations (typically ≥8×MIC), suggesting a benefit of higher β-lactam concentrations beyond those required for maximum initial killing.

Predicting and preventing antimicrobial resistance utilizing pharmacodynamics: part II Gram-negative bacteria

INTRODUCTION

Antimicrobial resistance is a serious health threat worldwide. Better understanding of exposure targets that could suppress resistance amplification is necessary to guide the dosing of currently available agents as well as new therapies in the drug development process. Areas covered: This review will discuss studies that focused on predicting development of resistance using the pharmacokinetic-pharmacodynamic approach and how to design dosing regimens that can successfully suppress resistance emergence in Gram-negative bacteria. Expert opinion: Pharmacokinetic-pharmacodynamic targets could provide useful insights to guide antimicrobial dosing to prevent resistance emergence. Exposure targets required for resistance suppression are higher than those for efficacy and might not be clinically feasible. Combination therapy is a possible approach to improve the efficacy and minimize the resistance emergence for difficult-to-treat infections.

Application of PK/PD Modeling in Veterinary Field: Dose Optimization and Drug Resistance Prediction

Among veterinary drugs, antibiotics are frequently used. The true mean of antibiotic treatment is to administer dose of drug that will have enough high possibility of attaining the preferred curative effect, with adequately low chance of concentration associated toxicity. Rising of antibacterial resistance and lack of novel antibiotic is a global crisis; therefore there is an urgent need to overcome this problem. Inappropriate antibiotic selection, group treatment, and suboptimal dosing are mostly responsible for the mentioned problem. One approach to minimizing the antibacterial resistance is to optimize the dosage regimen. PK/PD model is important realm to be used for that purpose from several years. PK/PD model describes the relationship between drug potency, microorganism exposed to drug, and the effect observed. Proper use of the most modern PK/PD modeling approaches in veterinary medicine can optimize the dosage for patient, which in turn reduce toxicity and reduce the emergence of resistance. The aim of this review is to look at the existing state and application of PK/PD in veterinary medicine based on in vitro, in vivo, healthy, and disease model.

Does High-Dose Antimicrobial Chemotherapy Prevent the Evolution of Resistance?

High-dose chemotherapy has long been advocated as a means of controlling drug resistance in infectious diseases but recent empirical studies have begun to challenge this view. We develop a very general framework for modeling and understanding resistance emergence based on principles from evolutionary biology. We use this framework to show how high-dose chemotherapy engenders opposing evolutionary processes involving the mutational input of resistant strains and their release from ecological competition. Whether such therapy provides the best approach for controlling resistance therefore depends on the relative strengths of these processes. These opposing processes typically lead to a unimodal relationship between drug pressure and resistance emergence. As a result, the optimal drug dose lies at either end of the therapeutic window of clinically acceptable concentrations. We illustrate our findings with a simple model that shows how a seemingly minor change in parameter values can alter the outcome from one where high-dose chemotherapy is optimal to one where using the smallest clinically effective dose is best. A review of the available empirical evidence provides broad support for these general conclusions. Our analysis opens up treatment options not currently considered as resistance management strategies, and it also simplifies the experiments required to determine the drug doses which best retard resistance emergence in patients.

The evolution of antimicrobial resistant pathogens threatens much of modern medicine. For over one hundred years, the advice has been to ‘hit hard’, in the belief that high doses of antimicrobials best contain resistance evolution. We argue that nothing in evolutionary theory supports this as a good rule of thumb in the situations that challenge medicine. We show instead that the only generality is to either use the highest tolerable drug dose or the lowest clinically effective dose; that is, one of the two edges of the therapeutic window. This approach suggests treatment options not currently considered, and simplifies the experiments required to identify the dose that best retards resistance evolution.

The path of least resistance: aggressive or moderate treatment?

The evolution of resistance to antimicrobial chemotherapy is a major and growing cause of human mortality and morbidity. Comparatively little attention has been paid to how different patient treatment strategies shape the evolution of resistance. In particular, it is not clear whether treating individual patients aggressively with high drug dosages and long treatment durations, or moderately with low dosages and short durations can better prevent the evolution and spread of drug resistance. Here, we summarize the very limited available empirical evidence across different pathogens and provide a conceptual framework describing the information required to effectively manage drug pressure to minimize resistance evolution.

Exploring the collaboration between antibiotics and the immune response in the treatment of acute, self-limiting infections

The successful treatment of bacterial infections is the product of a collaboration between antibiotics and the host's immune defenses. Nevertheless, in the design of antibiotic treatment regimens, few studies have explored the combined action of antibiotics and the immune response to clearing infections. Here, we use mathematical models to examine the collective contribution of antibiotics and the immune response to the treatment of acute, self-limiting bacterial infections. Our models incorporate the pharmacokinetics and pharmacodynamics of the antibiotics, the innate and adaptive immune responses, and the population and evolutionary dynamics of the target bacteria. We consider two extremes for the antibiotic-immune relationship: one in which the efficacy of the immune response in clearing infections is directly proportional to the density of the pathogen; the other in which its action is largely independent of this density. We explore the effect of antibiotic dose, dosing frequency, and term of treatment on the time before clearance of the infection and the likelihood of antibiotic-resistant bacteria emerging and ascending. Our results suggest that, under most conditions, high dose, full-term therapy is more effective than more moderate dosing in promoting the clearance of the infection and decreasing the likelihood of emergence of antibiotic resistance. Our results also indicate that the clinical and evolutionary benefits of increasing antibiotic dose are not indefinite. We discuss the current status of data in support of and in opposition to the predictions of this study, consider those elements that require additional testing, and suggest how they can be tested.

Conserving antibiotics for the future: new ways to use old and new drugs from a pharmacokinetic and pharmacodynamic perspective

There is a growing need to optimize the use of old and new antibiotics to treat serious as well as less serious infections. The topic of how to use pharmacokinetic and pharmacodynamic (PK/PD) knowledge to conserve antibiotics for the future was elaborated on in a workshop of the conference (The conference "The Global Need for Effective Antibiotics - moving towards concerted action", ReAct, Uppsala, Sweden, 2010). The optimization of dosing regimens is accomplished by choosing the dose and schedule that results in the antimicrobial exposure that will achieve the microbiological and clinical outcome desired while simultaneously suppressing emergence of resistance. PK/PD of antimicrobial agents describe how the therapeutic drug effect is dependent on the potency of a drug against a microorganism and the exposure (the concentration of antimicrobial available for effect over time). The description and modeling of these relationships quantitatively then allow for a rational approach to dose optimization and several strategies to that purpose are described. These strategies include not only the dosing regimen itself but also the duration of therapy, preventing collateral damage through inappropriate use and the application of PK/PD in drug development. Furthermore, PK/PD relationships of older antibiotics need to be urgently established. The need for global harmonization of breakpoints is also suggested and would add efficacy to antibiotic therapy. For each of the strategies, a number of priority actions are provided.

Attenuation of colistin bactericidal activity by high inoculum of Pseudomonas aeruginosa characterized by a new mechanism-based population pharmacodynamic model

Colistin is increasingly being utilized against Gram-negative pathogens, including Pseudomonas aeruginosa, resistant to all other antibiotics. Since limited data exist regarding killing by colistin at different initial inocula (CFUo), we evaluated killing of Pseudomonas aeruginosa by colistin at several CFUo and developed a mechanism-based mathematical model accommodating a range of CFUo. In vitro time-kill experiments were performed using >or=8 concentrations up to 64 x the MIC of colistin against P. aeruginosa PAO1 and two clinical P. aeruginosa isolates at CFUo of 10(6), 10(8), and 10(9) CFU/ml. Serial samples up to 24 h were simultaneously modeled in the NONMEM VI (results shown) and S-ADAPT software programs. The mathematical model was prospectively "validated" by additional time-kill studies assessing the effect of Ca(2+) and Mg(2+) on killing of PAO1 by colistin. Against PAO1, killing of the susceptible population was 23-fold slower at the 10(9) CFUo and 6-fold slower at the 10(8) CFUo than at the 10(6) CFUo. The model comprised three populations with different second-order killing rate constants (5.72, 0.369, and 0.00210 liters/h/mg). Bacteria were assumed to release signal molecules stimulating a phenotypic change that inhibits killing. The proposed mechanism-based model had a good predictive performance, could describe killing by colistin for all three studied strains and for two literature studies, and performed well in a prospective validation with various concentrations of Ca(2+) and Mg(2+). The extent and rate of killing of P. aeruginosa by colistin were markedly decreased at high CFUo compared to those at low CFUo. This was well described by a mechanism-based mathematical model, which should be further validated using dynamic in vitro models.