The effective concentrations of penicillin in vitro and in vivo for streptococci, pneumococci, and Treponema pallidum

Oral linezolid compared with benzathine penicillin G for treatment of early syphilis in adults (Trep-AB Study) in Spain: a prospective, open-label, non-inferiority, randomised controlled trial

BACKGROUND

Management of syphilis, a sexually transmitted infection (STI) with increasing incidence, is challenged by drug shortages, scarcity of randomised trial data, an absence of non-penicillin alternatives for pregnant women with penicillin allergy (other than desensitisation), extended parenteral administration for neurosyphilis and congenital syphilis, and macrolide resistance. Linezolid was shown to be active against Treponema pallidum, the causative agent of syphilis, in vitro and in the rabbit model. We aimed to assess the efficacy of linezolid for treating early syphilis in adults compared with the standard of care benzathine penicillin G (BPG).

METHODS

We did a multicentre, open-label, non-inferiority, randomised controlled trial to assess the efficacy of linezolid for treating early syphilis compared with BPG. We recruited participants with serological or molecular confirmation of syphilis (either primary, secondary, or early latent) at one STI unit in a public hospital and two STI community clinics in Catalonia (Spain). Participants were randomly allocated in a 1:1 ratio using a computer-generated block randomisation list with six participants per block, to receive either oral linezolid (600 mg once per day for 5 days) or intramuscular BPG (single dose of 2·4 million international units) and were assessed for signs and symptoms (once per week until week 6 and at week 12, week 24, and week 48) and reagin titres of non-treponemal antibodies (week 12, week 24, and week 48). The primary endpoint was treatment response, assessed using a composite endpoint that included clinical response, serological response, and absence of relapse. Clinical response was assessed at 2 weeks for primary syphilis and at 6 weeks for secondary syphilis following treatment initiation. Serological cure was defined as a four-fold decline in rapid plasma reagin titre or seroreversion at any of the 12-week, 24-week, or 48-week timepoints. The absence of relapse was defined as the presence of different molecular sequence types of T pallidum in recurrent syphilis. Non-inferiority was shown if the lower limit of the two-sided 95% CI for the difference in rates of treatment response was higher than -10%. The primary analysis was done in the per-protocol population. The trial is registered at ClinicalTrials.gov (NCT05069974) and was stopped for futility after interim analysis.

FINDINGS

Between Oct 20, 2021, and Sept 15, 2022, 62 patients were assessed for eligibility, and 59 were randomly assigned to linezolid (n=29) or BPG (n=30). In the per-protocol population, after 48 weeks' follow-up, 19 (70%) of 27 participants (95% CI 49·8 to 86·2) in the linezolid group had responded to treatment and 28 (100%) of 28 participants (87·7 to 100·0) in the BPG group (treatment difference -29·6, 95% CI -50·5 to -8·8), which did not meet the non-inferiority criterion. The number of drug-related adverse events (all mild or moderate) was similar in both treatment groups (five [17%] of 29, 95% CI 5·8 to 35·8 in the linezolid group vs five [17%] of 30, 5·6 to 34·7, in the BPG group). No serious adverse events were reported during follow-up.

INTERPRETATION

The efficacy of linezolid at a daily dose of 600 mg for 5 days did not meet the non-inferiority criteria compared with BPG and, as a result, this treatment regimen should not be used to treat patients with early syphilis.

FUNDING

European Research Council and Fondo de Investigaciones Sanitarias.

Translational PK/PD for the Development of Novel Antibiotics-A Drug Developer's Perspective

Antibiotic development traditionally involved large Phase 3 programs, preceded by Phase 2 studies. Recognizing the high unmet medical need for new antibiotics and, in some cases, challenges to conducting large clinical trials, regulators created a streamlined clinical development pathway in which a lean clinical efficacy dataset is complemented by nonclinical data as supportive evidence of efficacy. In this context, translational Pharmacokinetic/Pharmacodynamic (PK/PD) plays a key role and is a major contributor to a "robust" nonclinical package. The classical PK/PD index approach, proven successful for established classes of antibiotics, is at the core of recent antibiotic approvals and the current antibacterial PK/PD guidelines by regulators. Nevertheless, in the case of novel antibiotics with a novel Mechanism of Action (MoA), there is no prior experience with the PK/PD index approach as the basis for translating nonclinical efficacy to clinical outcome, and additional nonclinical studies and PK/PD analyses might be considered to increase confidence. In this review, we discuss the value and limitations of the classical PK/PD approach and present potential risk mitigation activities, including the introduction of a semi-mechanism-based PK/PD modeling approach. We propose a general nonclinical PK/PD package from which drug developers might choose the studies most relevant for each individual candidate in order to build up a "robust" nonclinical PK/PD understanding.

Beta-Lactam Dose Optimisation in the Intensive Care Unit: Targets, Therapeutic Drug Monitoring and Toxicity

Beta-lactams are an important family of antibiotics used to treat infections and are commonly used in critically ill patients. Optimal use of these drugs in the intensive care unit (ICU) is important because of the serious complications from sepsis. Target beta-lactam antibiotic exposures may be chosen using fundamental principles of beta-lactam activity derived from pre-clinical and clinical studies, although the debate regarding optimal beta-lactam exposure targets is ongoing. Attainment of target exposures in the ICU requires overcoming significant pharmacokinetic (PK) and pharmacodynamic (PD) challenges. For beta-lactam drugs, the use of therapeutic drug monitoring (TDM) to confirm if the desired exposure targets are achieved has shown promise, but further data are required to determine if improvement in infection-related outcomes can be achieved. Additionally, beta-lactam TDM may be useful where a relationship exists between supratherapeutic antibiotic exposure and drug adverse effects. An ideal beta-lactam TDM service should endeavor to efficiently sample and report results in identified at-risk patients in a timely manner. Consensus beta-lactam PK/PD targets associated with optimal patient outcomes are lacking and should be a focus for future research.

ADME, Pharmacokinetic Scaling, Pharmacodynamic and Prediction of Human Dose and Regimen of Novel Antiviral Drugs

The search for new drugs is an extremely time-consuming and expensive endeavour. Much of that time and money go into generating predictive human pharmacokinetic profiles from preclinical efficacy and safety animal data. These pharmacokinetic profiles are used to prioritize or minimize the attrition at later stages of the drug discovery process. In the area of antiviral drug research, these pharmacokinetic profiles are equally important for the optimization, estimation of half-life, determination of effective dose, and dosing regimen, in humans. In this article we have highlighted three important aspects of these profiles. First, the impact of plasma protein binding on two primary pharmacokinetic parameters-volume of distribution and clearance. Second, interdependence of primary parameters on unbound fraction of the drug. Third, the ability to extrapolate human pharmacokinetic parameters and concentration time profiles from animal profiles.

Penicillin Treatment Failure in Rabbit Syphilis Due to the Persistence of Treponemes (Treponema paraluisleporidarum Ecovar Cuniculus) in the Focus of Infection

Rabbit venereal spirochetosis, a disease caused by Treponema paraluisleporidarum ecovar Cuniculus (TPeC), affects both wild and pet rabbits, and is transmitted sexually and via direct contact among animals. Treatment of syphilis in pet rabbits requires administration of antibiotics, including penicillin G, chloramphenicol, or fluoroquinolones. The aim of this work was to elucidate the cause of penicillin treatment failure in rabbit syphilis in a pet rabbit treated in Brno, Czech Republic, and to assess the phylogenetic relatedness of the agent to previously characterized pathogenic treponemes. Following amputation of the infected digits, the second round of penicillin treatment using the same dosage and application route resulted in the disappearance of clinical symptoms within a period of two weeks. The bacterium was successfully isolated from the claws, propagated in three experimental rabbits, and the resulting TPeC strain was designated as Cz-2020. Analysis of four genetic loci revealed that the Cz-2020 strain was similar but also clearly distinct from the only TPeC strain, which had been characterized in detail to date, i.e., the Cuniculi A strain, which was isolated in North America. The strain Cz-2020 represents the first available viable TPeC strain of European origin. DNA sequences encoding five penicillin-binding proteins of the strain Cz-2020 were compared to those of Cuniculi A, which is known to be sensitive to penicillin. The sequences differed in six nucleotides resulting in single amino acid changes in Penicillin-binding protein 1, 2, and 3. Since the second round of treatment was successful, we conclude that the penicillin treatment failure in the first round resulted from the presence of infection foci in claws where treponemes persisted.

Towards precision medicine: Therapeutic drug monitoring-guided dosing of vancomycin and β-lactam antibiotics to maximize effectiveness and minimize toxicity

PURPOSE

The goal of this review is to explore the role of antimicrobial therapeutic drug monitoring (TDM), especially in critically ill, obese, and older adults, with a specific focus on β-lactams and vancomycin.

SUMMARY

The continued rise of antimicrobial resistance prompts the need to optimize antimicrobial dosing. The aim of TDM is to individualize antimicrobial dosing to achieve antibiotic exposures associated with improved patient outcomes. Initially, TDM was developed to minimize adverse effects during use of narrow therapeutic index agents. Today, patient and organism complexity are expanding the need for precision dosing through TDM services. Alterations of pharmacokinetics and pharmacodynamics (PK/PD) in the critically ill, obese, and older adult populations, in conjunction with declining organism susceptibility, complicate attainment of therapeutic targets. Over the last decade, antimicrobial TDM has expanded with the emergence of literature supporting β-lactam TDM and a shift from monitoring vancomycin trough concentrations to monitoring of the ratio of area under the concentration (AUC) curve to minimum inhibitory concentration (MIC). PK/PD experts should be at the forefront of implementing precision dosing practices.

CONCLUSION

Precision dosing through TDM is expanding and is especially important in populations with altered PK/PD, including critically ill, obese, and older adults. Due to wide PK/PD variability in these populations, TDM is vital to maximize antimicrobial effectiveness and decrease adverse event rates. However, there is still a need for studies connecting TDM to patient outcomes. Providing patient-specific care through β-lactam TDM and transitioning to vancomycin AUC/MIC monitoring may be challenging, but with experts at the forefront of this initiative, PK-based optimization of antimicrobial therapy can be achieved.

Combating Multidrug-Resistant Bacteria by Integrating a Novel Target Site Penetration and Receptor Binding Assay Platform Into Translational Modeling

Multidrug-resistant bacteria are causing a serious global health crisis. A dramatic decline in antibiotic discovery and development investment by pharmaceutical industry over the last decades has slowed the adoption of new technologies. It is imperative that we create new mechanistic insights based on latest technologies, and use translational strategies to optimize patient therapy. Although drug development has relied on minimal inhibitory concentration testing and established in vitro and mouse infection models, the limited understanding of outer membrane permeability in Gram-negative bacteria presents major challenges. Our team has developed a platform using the latest technologies to characterize target site penetration and receptor binding in intact bacteria that inform translational modeling and guide new discovery. Enhanced assays can quantify the outer membrane permeability of β-lactam antibiotics and β-lactamase inhibitors using multiplex liquid chromatography tandem mass spectrometry. While β-lactam antibiotics are known to bind to multiple different penicillin-binding proteins (PBPs), their binding profiles are almost always studied in lysed bacteria. Novel assays for PBP binding in the periplasm of intact bacteria were developed and proteins identified via proteomics. To characterize bacterial morphology changes in response to PBP binding, high-throughput flow cytometry and time-lapse confocal microscopy with fluorescent probes provide unprecedented mechanistic insights. Moreover, novel assays to quantify cytosolic receptor binding and intracellular drug concentrations inform target site occupancy. These mechanistic data are integrated by quantitative and systems pharmacology modeling to maximize bacterial killing and minimize resistance in in vitro and mouse infection models. This translational approach holds promise to identify antibiotic combination dosing strategies for patients with serious infections.

Combatting the Rising Tide of Antimicrobial Resistance: Pharmacokinetic/Pharmacodynamic Dosing Strategies for Maximal Precision

OBJECTIVE

Antimicrobial pharmacokinetics/pharmacodynamics (PK/PD) principles and PK/PD models have been essential in characterizing the mechanism of antibiotic bacterial killing and determining the most optimal dosing regimen that maximizes clinical outcomes. This review summarized the fundamentals of antimicrobial PK/PD and the various types of PK/PD experiments that shaped the utilization and dosing strategies of antibiotics today.

METHODS

Multiple databases - including PubMed, Scopus, and EMBASE - were searched for published articles that involved PK/PD modelling and precision dosing. Data from in vitro, in vivo and mechanistic PK/PD models were reviewed as a basis for compiling studies that guide dosing regimens used in clinical trials.

RESULTS

Literature regarding the utilization of exposure-response analyses, mathematical modelling and simulations that were summarized are able to provide a better understanding of antibiotic pharmacodynamics that influence translational drug development. Optimal pharmacokinetic sampling of antibiotics from patients can lead to personalized dosing regimens that attain target concentrations while minimizing toxicity. Thus the development of a fully integrated mechanistic model based on systems pharmacology can continually adapt to data generated from clinical responses, which can provide the framework for individualized dosing regimens.

CONCLUSIONS

The promise of what PK/PD can provide through precision dosing for antibiotics has not been fully realized in the clinical setting. Antimicrobial resistance, which has emerged as a significant public health threat, has forced clinicians to empirically utilize therapies. Future research focused on implementation and translation of PK/PD-based approaches integrating novel approaches that combine knowledge of combination therapies, systems pharmacology and resistance mechanisms are necessary. To fully realize maximally precise therapeutics, optimal PK/PD strategies are critical to maximize antimicrobial efficacy against extremely-drug-resistant organisms, while minimizing toxicity.

Phase II trial evaluating the clinical efficacy of cefixime for treatment of active syphilis in non-pregnant women in Brazil (CeBra)

BACKGROUND

Syphilis is a sexually and vertically transmitted infection caused by the bacteria Treponema pallidum for which there are few proven alternatives to penicillin for treatment. For pregnant women infected with syphilis, penicillin is the only WHO-recommended treatment that will treat the mother and cross the placenta to treat the unborn infant and prevent congenital syphilis. Recent shortages, national level stockouts as well as other barriers to penicillin use call for the urgent identification of alternative therapies to treat pregnant women infected with syphilis.

METHODS

This prospective, randomized, non-comparative trial will enroll non-pregnant women aged 18 years and older with active syphilis, defined as a positive rapid treponemal and a positive non-treponemal RPR test with titer ≥1:16. Women will be a, domized in a 2:1 ratio to receive the oral third generation cephalosporin cefixime at a dose of 400 mg two times per day for 10 days (n = 140) or benzathine penicillin G 2.4 million units intramuscularly based on the stage of syphilis infection (n = 70). RPR titers will be collected at enrolment, and at three, six, and nine months following treatment. Participants experiencing a 4-fold (2 titer) decline by 6 months will be considered as having an adequate or curative treatment response.

DISCUSSION

Demonstration of efficacy of cefixime in the treatment of active syphilis in this Phase 2 trial among non-pregnant women will inform a proposed randomized controlled trial to evaluate cefixime as an alternative treatment for pregnant women with active syphilis to evaluate prevention of congenital syphilis.

TRIAL REGISTRATION

Trial identifier: www.Clinicaltrials.gov, NCT03752112. Registration Date: November 22, 2018.

Animal Models for Drug Development for MRSA

One of the foremost challenges of drug discovery in any therapeutic area is that of solidifying the correlation between in vitro activity and clinical efficacy. Between these is the confirmation that affecting a particular target in vivo will lead to a therapeutic benefit. In antibacterial drug discovery, there is a key advantage from the start, since the targets are bacteria-therefore, it is simple to ascertain in vitro whether a drug has the desired effect, i.e., bacterial cell inhibition or killing, and to understand the mechanism by which that occurs. The downstream criteria, whether a compound reaches the infection site and achieves appropriately high levels to affect bacterial viability, can be evaluated in animal models of infection. In this way animal models of infection can be a highly valuable and predictive bridge between in vitro drug discovery and early clinical evaluation.The Gram-positive pathogen Staphylococcus aureus causes a wide variety of infections in humans (Archer, Clin Infect Dis 26:1179-1181, 1998), and has been said to be able to infect every tissue type. Fortunately, over the years a great deal of effort has been expended toward developing infection models in rodents using this organism, with good success. This chapter describes the advantages, setups, and outcome measurements of the rodent models most used in drug discovery for S. aureus. Mouse models will be the focus of this chapter, as they are the most economical and thus most commonly used, but a rat infection model is included as well.

Target attainment with continuous dosing of piperacillin/tazobactam in critical illness: a prospective observational study

Optimal dosing of β-lactam antibiotics in critically ill patients is a challenge given the unpredictable pharmacokinetic profile of this patient population. Several studies have shown intermittent dosing to often yield inadequate drug concentrations. Continuous dosing is an attractive alternative from a pharmacodynamic point of view. This study evaluated whether, during continuous dosing, piperacillin concentrations reached and maintained a pre-defined target in critically ill patients. Adult patients treated with piperacillin by continuous dosing in the intensive care unit of a university medical centre in The Netherlands were prospectively studied. Total and unbound piperacillin concentrations drawn at fixed time points throughout the entire treatment course were determined by liquid chromatography-tandem mass spectrometry. A pharmacokinetic combined target of a piperacillin concentration ≥80 mg/L, reached within 1 h of starting study treatment and maintained throughout the treatment course, was set. Eighteen patients were analysed. The median duration of monitored piperacillin treatment was 60 h (interquartile range, 33-96 h). Of the 18 patients, 5 (27.8%) reached the combined target; 15 (83.3%) reached and maintained a less strict target of >16 mg/L. In this patient cohort, this dosing schedule was insufficient to reach the pre-defined target. Depending on which target is to be met, a larger initial cumulative dose is desirable, combined with therapeutic drug monitoring.

Pharmacodynamic Properties of Antibiotics: Application to Drug Monitoring and Dosage Regimen Design

The goal of antimicrobial chemotherapy is to effectively eradicate pathogenic organisms while minimizing the likelihood of drug-related adverse effects. In this era of cost containment, consideration should also be given to performing this task with the smallest total dose of drug and the shortest duration of therapy. Determination of the appropriate dose and dosing interval of an antimicrobial requires knowledge and integration of both its pharmacokinetic and pharmacodynamic properties.

UK national guidelines on the management of syphilis 2015

These guidelines are an update for 2015 of the 2008 UK guidelines for the management of syphilis. The writing group have piloted the new BASHH guideline methodology, notably using the GRADE system for assessing evidence and making recommendations. We have made significant changes to the recommendations for screening infants born to mothers with positive syphilis serology and to facilitate accurate and timely communication between the teams caring for mother and baby we have developed a birth plan. Procaine penicillin is now an alternative, not preferred treatment, for all stages of syphilis except neurosyphilis, but the length of treatment for this is shortened. Other changes are summarised at the start of the guideline.

Animal models in drug development for MRSA

One of the foremost challenges of drug discovery in any therapeutic area is that of solidifying the correlation between in vitro activity and clinical efficacy. Between these is the confirmation that affecting a particular target in vivo will lead to a therapeutic benefit. In antibacterial drug discovery, there is a key advantage from the start, since the targets are bacteria-therefore, it is simple to ascertain in vitro whether a drug has the desired effect, i.e., bacterial cell inhibition or killing, and to understand the mechanism by which that occurs. The downstream criteria, whether a compound reaches the infection site and achieves appropriately high levels to affect bacterial viability, can be evaluated in animal models of infection. In this way animal models of infection can be a highly valuable and predictive bridge between in vitro drug discovery and early clinical evaluation.The Gram-positive pathogen Staphylococcus aureus causes a wide variety of infections in humans (Archer, Clin Infect Dis 26:1179-1181, 1998) and has been said to be able to infect every tissue type. Fortunately, over the years a great deal of effort has been expended toward developing infection models in rodents using this organism, with good success. This chapter will describe the advantages, methods, and outcome measurements of the rodent models most used in drug discovery for S. aureus. Mouse models will be the focus of this chapter, as they are the most economical and thus most commonly used, but a rat infection model is included as well.

Understanding pharmacokinetics to improve tuberculosis treatment outcome

INTRODUCTION

Tuberculosis (TB) remains the leading cause of death from a curable infectious disease; drug-resistant TB threatens to dismantle all prior gains in global control. Suboptimal circulating anti-TB drug concentrations can lead to lack of cure and acquired drug resistance.

AREAS COVERED

This review will introduce pharmacokinetic parameters for key anti-TB drugs, as well as the indications and limitations of measuring these parameters in clinical practice. Current and novel methodologies for delivering anti-TB pharmacokinetic-pharmacodynamic data are highlighted and gaps in operational research described.

EXPERT OPINION

Individual pharmacokinetic variability is commonplace, underappreciated and difficult to predict without therapeutic drug monitoring (TDM). Pharmacokinetic thresholds associated with poor TB treatment outcome in drug-susceptible TB have recently been described and may now guide the application of TDM, but require validation in a variety of settings and comorbidities. Dried blood spots for TDM and prepackaged multidrug plates for minimum inhibitory concentration testing will overcome barriers of accessibility and represent areas for innovation. Operationalizing pharmacokinetics has the potential to improve TB outcomes in the most difficult-to-treat forms of the disease such as multidrug resistance. Clinical studies in these areas are eagerly anticipated and we expect will better define the rational introduction of novel therapeutics.

Nonlinear pharmacokinetics of piperacillin in healthy volunteers--implications for optimal dosage regimens

AIMS

(i) To describe the first-order and mixed-order elimination pathways of piperacillin, (ii) to determine the between occasion variability (BOV) of pharmacokinetic parameters and (iii) to propose optimized dosage regimens.

METHODS

We performed a five-period replicate dose study in four healthy volunteers. Each subject received 4g piperacillin as a single 5min intravenous infusion in each study period. Drug analysis was performed by HPLC. We used NONMEM and S-ADAPT for population pharmacokinetic analysis and Monte Carlo simulation to predict the probability of target attainment (PTA) with a target time of non-protein bound concentration above MIC >50% of the dosing interval.

RESULTS

A model with first-order nonrenal elimination and parallel first-order and mixed-order renal elimination had the best predictive performance. For a 70kg subject we estimated 4.40lh(-1) for nonrenal clearance, 5.70lh(-1) for first-order renal clearance, 170mgh(-1) for V(max) , and 49.7mgl(-1) for K(m) for the mixed-order renal elimination. The BOV was 39% for V(max) , 117% for K(m) , and 8.5% for total clearance. A 30min infusion of 4g every 6h achieved robust (≥90%) PTAs for MICs ≤12mgl(-1) . As an alternative mode of administration, a 5h infusion of 6g every 8h achieved robust PTAs for MICs ≤48mgl(-1) .

CONCLUSIONS

Part of the renal elimination of piperacillin is saturable at clinically used doses. The BOV of total clearance and volume of distribution were low. Prolonged infusions achieved better PTAs compared with shorter infusions at similar daily doses. This benefit was most pronounced for MICs between 12 and 48mgl(-1) .

Pharmacokinetics-pharmacodynamics of gatifloxacin in a lethal murine Bacillus anthracis inhalation infection model

We determined the pharmacokinetic-pharmacodynamic (PK-PD) measure most predictive of gatifloxacin efficacy and the magnitude of this measure necessary for survival in a murine Bacillus anthracis inhalation infection model. We then used population pharmacokinetic models for gatifloxacin and simulation to identify dosing regimens with high probabilities of attaining exposures likely to be efficacious in adults and children. In this work, 6- to 8-week-old nonneutropenic female BALB/c mice received aerosol challenges of 50 to 75 50% lethal doses of B. anthracis (Ames strain, for which the gatifloxacin MIC is 0.125 mg/liter). Gatifloxacin was administered at 6- or 8-h intervals beginning 24 h postchallenge for 21 days, and dosing was designed to produce profiles mimicking fractionated concentration-time profiles for humans. Mice were evaluated daily for survival. Hill-type models were fitted to survival data. To identify potentially effective dosing regimens, adult and pediatric population pharmacokinetic models for gatifloxacin and Monte Carlo simulation were used to generate 5,000 individual patient exposure estimates. The ratio of the area under the concentration-time curve from 0 to 24 h (AUC(0-24)) to the MIC of the drug for the organism (AUC(0-24)/MIC ratio) was the PK-PD measure most predictive of survival (R(2) = 0.96). The 50% effective dose (ED(50)) and the ED(90) and ED(99) corresponded to AUC(0-24)/MIC ratios of 11.5, 15.8, and 30, respectively, where the maximum effect was 97% survival. Simulation results indicate that a daily gatifloxacin dose of 400 mg for adults and 10 mg/kg of body weight for children gives a 100% probability of attaining the PK-PD target (ED(99)). Sensitivity analyses suggest that the probability of PK-PD target attainment in adults and children is not affected by increases in MICs for strains of B. anthracis to levels as high as 0.5 mg/liter.

Antimicrobial stewardship and the role of pharmacokinetics-pharmacodynamics in the modern antibiotic era

Antimicrobial stewardship, a term coined by Dale Gerding, is defined as the optimal selection, dose, and duration of an antimicrobial that results in the best clinical outcome for the treatment or prevention of infection, with minimal toxicity to the patient and minimal impact on subsequent resistance development. Methods to promote and ensure good antimicrobial stewardship have been implemented and studied, and have typically provided tangible benefits in terms of a reduction in overall or targeted antimicrobial usage and resistance emergence. Although most of the programmatic antimicrobial stewardship efforts have been conducted in acute care inpatient settings, some strategies usually involving education have been evaluated in the outpatient venue. In this review, we shall discuss issues related to why antimicrobial stewardship is of particular importance in the modern antibiotic era. In addition, general pharmacokinetic-pharmacodynamic (PK-PD) concepts will be reviewed and specific PK-PD analyses that support the optimal selection, dosing, and duration of therapy for beta-lactam antimicrobials will be provided.

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

Since the advent of the modern era of antimicrobial chemotherapy in the 1930s, animal infection models have allowed for the in vivo evaluation of antimicrobial agents for the treatment of experimentally induced infection. Today, animal pharmacokinetic-pharmacodynamic (PK-PD) infection models serve as a cornerstone of the preclinical assessment process for antibacterial agents and dose and dosing interval selection, as decision support for setting in vitro susceptibility breakpoints, and, finally, for the evaluation of the meaning of in vitro resistance. Over the past 15 years, considerable PK-PD data have been derived from infected patients for many classes of antimicrobial agents. These data provide the opportunity to confirm knowledge gained from animal PK-PD infection models.

Clindamycin in the treatment of group G beta-haemolytic streptococcal infections

We report a case of severe streptococcal cellulitis in a healthy 47 year old male, where the sole microbial isolate was a beta-haemolytic group G Streptococcus. Treatment failure with high dose penicillin was observed despite in vitro sensitivity. The addition of clindamycin resulted in dramatic clinical improvement. This may indicate an Eagle-type effect (whereby antibiotics exhibit paradoxically reduced bactericidal activities at high drug concentrations), in group G beta-haemolytic infections. Although well documented with group A streptococcal infections, this phenomenon has not been fully recognised with group G beta-haemolytic streptococcal infections. This may have important implications for clinical management.

GlpD and PlsB participate in persister cell formation in Escherichia coli

Bacterial populations produce dormant persister cells that are resistant to killing by all antibiotics currently in use, a phenomenon known as multidrug tolerance (MDT). Persisters are phenotypic variants of the wild type and are largely responsible for MDT of biofilms and stationary populations. We recently showed that a hipBA toxin/antitoxin locus is part of the MDT mechanism in Escherichia coli. In an effort to find additional MDT genes, an E. coli expression library was selected for increased survival to ampicillin. A clone with increased persister production was isolated and was found to overexpress the gene for the conserved aerobic sn-glycerol-3-phosphate dehydrogenase GlpD. The GlpD overexpression strain showed increased tolerance to ampicillin and ofloxacin, while a strain with glpD deleted had a decreased level of persisters in the stationary state. This suggests that GlpD is a component of the MDT mechanism. Further genetic studies of mutants affected in pathways involved in sn-glycerol-3-phosphate metabolism have led to the identification of two additional multidrug tolerance loci, glpABC, the anaerobic sn-glycerol-3-phosphate dehydrogenase, and plsB, an sn-glycerol-3-phosphate acyltransferase.

Evolution of a new drug formulation: the rationale for high-dose, short-course therapy with azithromycin

The rationale for the use of high-dose, short-course azithromycin treatment regimens is based on the pharmacokinetic properties of azithromycin. Its long elimination half-life (approximately 60 h) and antibacterial potency make short-course (1-day) regimens feasible. Azithromycin is concentrated within phagocytic cells, which deliver it in a targeted manner to sites of infection. In vitro and in vivo models demonstrate that azithromycin is taken up, transported and released at the sites of infection by polymorphonuclear neutrophils and macrophages. Uptake is not saturable, so delivery of the total azithromycin therapeutic regimen as a single dose of azithromycin microspheres should lead to increased uptake and delivery of the drug to sites of infection. By achieving higher drug concentrations at the site of infection, a single, high dose of azithromycin microspheres should maximize efficacy. The new microsphere formulation allows for 'front loading' of the dose to achieve the highest drug levels early in the course of infection while maintaining favorable tolerability.

[Syphilis treatment. German and international guidelines--a comparison]

Guidelines are an important instrument for improving the quality of medical care. In 2001, the German STD Society (DSTDG) published guidelines for syphilis diagnostics and treatment. For two reasons, these guidelines had to be reviewed urgently: Firstly, there is an obvious "renaissance" of syphilis among men having sex with men, which is complicated by a frequent comorbidity with HIV infection. Secondly, the standard drug for syphilis treatment in Germany, clemizole penicillin, has no longer been available since July 2003. In this article, the new German guidelines for syphilis treatment 2004, published by the DSTDG, are compared with other syphilis guidelines, which are valid for the European countries, i.e., the CDC, UK, Russian, and European guidelines 2002.

Antimicrobial drug delivery in food animals and microbial food safety concerns: an overview of in vitro and in vivo factors potentially affecting the animal gut microflora

This review provides an overview of considerations particular to the delivery of antimicrobial agents to food animals. Antimicrobial drugs are used in food animals for a variety of purposes. These drugs may have therapeutic effects against disease agents, or may cause changes in the structure and/or function of systems within the target animal. Routes of administration, quantity, duration, and potency of an antimicrobial drug are all important factors affecting their action(s) and success. Not only might targeted pathogens be affected, but also bacteria residing in (or on) the treated food animals, especially in the intestines (gastrointestinal tract microflora). Resistance to antimicrobial agents can occur through a number of mechanisms. The extent to which resistance develops is greatly affected by the amount of drug [or its metabolite(s)] a bacterium is exposed to, the duration of exposure, and the interaction between an individual antimicrobial agent and a particular bacterium. The impact of antimicrobial agents on the emergence of resistance in vitro and in vivo may not readily correlate.

Rationale for single and high dose treatment regimens with azithromycin

The rationale for the use of single dose and shorter course azithromycin treatment regimens is based on the pharmacokinetic properties of azithromycin. The drug has a long elimination half-life (>50 h), which enables short course 1- or 3-day dose regimens to be clinically effective. Azithromycin is concentrated within phagocytic cells and tissues and it achieves targeted delivery by these cells to sites of infection. In vitro and in vivo models have demonstrated that azithromycin is taken up, transported and released at the sites of infection by phagocytic cells such as polymorphonuclear neutrophils and macrophages. Uptake is not saturable; therefore delivery of the total dose of azithromycin as a 1- or 3-day regimen should lead to increased uptake and delivery of the drug to sites of infection.

Clinical pharmacodynamics of quinolones

An understanding of fundamental PK-PD principles forms the basis for the rational use of antimicrobial agents. For quinolones, the fAUC24:MIC ratio is predictive of efficacy in animal and in vitro infection models, and in infected patients. The magnitude of the fAUC24:MIC ratio predictive of efficacy in animal and in vitro infection models has been shown to be concordant with those obtained from human data. By accounting for PK and microbiologic variability together with PK-PD targets associated with efficacy or resistance suppression by Monte Carlo simulation, it is possible to discriminate between therapeutic regimens and select those regimens likely to be of greater benefit to patients. The maturation of antimicrobial PK-PD as a scientific discipline continues to accelerate and currently impacts clinical practice, drug development, and regulatory decision making.

Penicillin concentrations in sera and tonsils after intramuscular administration of benzathine penicillin G to children

BACKGROUND

The optimal regimen of benzathine penicillin G for secondary prevention of rheumatic fever is controversial. Data from serum pharmacokinetic studies do not fully agree on the period of protection after drug administration. Data from concentration of penicillin in tonsils may provide additional information.

METHODS

To evaluate penicillin concentrations in palatine tonsils and in sera 1, 10, 14 and 21 days after intramuscular injection of benzathine penicillin G 40,000 IU/kg, 58 children between 4 and 12 years of age with chronic tonsillitis and indication for tonsillectomy were given the study drug 1, 10, 14 or 21 days before surgery. Blood and tonsil samples were obtained during surgery, and penicillin concentrations were determined microbiologically by the agar well diffusion technique.

RESULTS

Mean serum penicillin concentrations 1, 10, 14 and 21 days after drug administration were, respectively, 0.080, 0.031, 0.023 and 0.014 microg/ml. Mean penicillin concentrations in tonsils at 1, 10, 14 and 21 days were 0.023, 0.010, 0.007 and 0.002 microg/g, respectively. Detectable penicillin concentration in tonsils (method sensitivity, 0.006 microg/g) was obtained in all patients on Day 1 and in 91% and 83.3% of patients on Days 10 and 14, respectively. By Day 21 this proportion was reduced to 30%.

CONCLUSIONS

The results of this study suggest that penicillin values may be inadequate for prevention of rheumatic fever by Week 3 of administration in a majority of children.

Optimizing antimicrobial dosing in the critically ill patient

"We know everything about antibiotics except how much to give," Maxwell Finland once stated. Finally, with the proliferation of pharmacodynamics as a science, we are addressing the question of how much to give. We have moved from an era of more or less arbitrary antimicrobial dosage selection toward one characterized by evidence-based optimal dosing strategies. Optimizing antimicrobial therapy in critically ill patients is more than just the selection of a suitable dose for a particular patient. Optimizing therapy also involves the selection of an appropriate single or combination antibiotic regimen that is active against the suspected or documented pathogens at the site(s) of infection. The regimen should offer the fewest potential adverse events, and the duration of therapy should be the shortest possible so as not to encourage resistance. Dosing of the chosen regimen should reflect variables that are often ignored, such as the patient's weight and age. The new continuous renal replacement therapies are commonly used in the critical care unit and must be considered. Finally, the cost of the regimen should be considered, but not only the cost to purchase the chosen antimicrobial agent but the cost to administer it (, the cost of minibags or syringes, intravenous tubing, saline flushes [all multiplied by the number of times per day the drug is given]), and, most importantly, if the patient fails to respond to therapy, the cost necessary to re-treat the patient to bring about a cure. In this review, we discuss some of the principles required to optimize antimicrobial dosing and recently obtained data regarding its application to the critically ill patient.

Management issues in syphilis

Syphilis is a sexually transmitted infection which is systemic from the outset and has increased in incidence worldwide over the last decade. There has been concern as to whether or not co-infection with HIV can modify the clinical presentation of syphilis and, as a genital ulcer disease, it can facilitate the transmission of HIV infection. Diagnosis is based on the microscopic identification of the causative treponeme and serological testing. Recommendations for the treatment of syphilis have been based on expert opinion, case series, some clinical trials and 50 years of clinical experience. Penicillin, given intramuscularly, is the mainstay of treatment and the favoured preparations for early infectious syphilis are benzathine penicillin as a single injection or a course of daily procaine penicillin injections for 10 to 14 days. The duration of treatment is longer for late syphilis. There has been concern that benzathine penicillin may not prevent the development of neurosyphilis but that is a rare outcome with this therapy. The main alternative to penicillin is doxycycline, but the place of azithromycin and ceftriaxone is yet to be established. It is not necessary to carry out examination of the cerebrospinal fluid in patients with early infectious syphilis but it should be performed in those with neurological or ocular signs, psychiatric signs or symptoms, when there is evidence of treatment failure and in those who are co-infected with HIV. Follow-up is an essential part of management and should be particularly assiduous, for at least 24 months, in those co-infected with HIV. Partner notification should be mandatory to try to contain the spread of infection.

Antimicrobial pharmacodynamics

The ultimate goal of antimicrobial therapy is to provide the best possible outcomes for patients. For this to occur, the clinician should be cognizant of many clinical, microbiologic, pharmacologic, and epidemiologic data as well as fundamental pharmacodynamic concepts. An understanding of pharmacodynamic principles is essential; it forms the scientific basis for the design of dosing strategies that maximize clinical efficacy and minimize toxicity. In the 1990s, data accumulated from in vitro models of infection, animal models of infection, healthy volunteer studies, and clinical trials that have expanded knowledge on how drugs best kill microorganisms. This knowledge has enabled clinicians to establish the best modes of antibiotic administration to maximize the killing of microorganisms and to optimize clinical outcomes.

Concentrations of procaine and aqueous penicillin in the cerebrospinal fluid of infants treated for congenital syphilis

Penicillin concentrations in cerebrospinal fluid (CSF) were measured at various hours and days of treatment in 163 infants undergoing therapy for congenital syphilis. The CSF levels were compared for three treatment regimens. Aqueous penicillin G (A-PEN), 100,000 U/kg per day, was used in 23 infant, and a dosage of 200,000 U/kg per day was used in 40 patients; procaine penicillin G (P-PEN), 50,000 U/kg per day, was used in 100 children. Mean CSF penicillin levels were 0.416, 0.493, and 0.077 microgram/ml, respectively, in the three treatment groups. The mean CSF penicillin concentration among the 63 infants treated with either of the A-PEN regimens (0.465 microgram/ml) was significantly greater than the mean concentration (0.077 microgram/ml) among those treated with P-PEN (p < 0.001). Among those who received A-PEN, the difference in dosage was not associated with a significant difference in mean CSF penicillin concentration (p = 0.68). All the specimens obtained from patients who received A-PEN, but only 82% of those from patients who received P-PEN, had treponemicidal concentrations (> or = 0.018 microgram/ml). However, 33.3% (9/27) of specimens from infants who received P-PEN, tested between 18 and 24 hours after a dose, had CSF penicillin concentrations < 0.018 microgram/ml. These data suggest that administration of A-PEN may be the preferred therapy if CSF levels > 0.018 microgram/ml are desired, especially for infants with severe disease or congenital neurosyphilis.

A review and update on adult syphilis, with particular reference to its treatment

Syphilis has become less common in Europe in the last decade, but has once again become a major problem in the USA, and remains so in many developing countries. Several treponemal genes have now been cloned and expressed in Escherichia coli, allowing study of treponemal proteins. The importance of cell mediated immunity in syphilis has been demonstrated in animal models. A diagnosis of syphilis is usually confirmed by dark-field microscopy or serological tests. Seroconversion may be delayed in HIV infected individuals. A positive reaginic test in cerebrospinal fluid (CSF) has a high specificity but low sensitivity in the diagnosis of neurosyphilis. Indeed, virulent treponemes can be identified in CSF samples which have negative reaginic tests, normal cell counts and protein levels. In the CSF, the FTA-Abs test has a high sensitivity but low specificity for neurosyphilis. Penicillin remains the treatment of choice for all stages of syphilis, although it penetrates the blood brain barrier poorly. Treatment with intramuscular benzathine penicillin 2.4 million units stat, or 600,000 units procaine penicillin daily does not produce treponemicidal levels within the CSF. However, the incidence of neurosyphilis is low in immunocompetent patients treated with such regimens during early syphilis. Acceptable alternatives in penicillin-allergic patients include ceftriaxone and doxycycline. Erythromycin is not recommended as it has produced unacceptably high rates of treatment failure. Recently, a strain of macrolide-resistant Treponema pallidum was isolated from a patient with secondary syphilis. For the treatment of neurosyphilis, treponemicidal levels of penicillin can be achieved in the CSF using 2.4 million units procaine penicillin daily with concurrent probenecid 500 mg 4 times a day, or an intravenous infusion of benzyl penicillin 12-24 million units daily. Early syphilis can be treated adequately over 10 days, but 21 to 28 days is appropriate for late syphilis. In HIV-infected patients syphilis may present atypically with initially negative serological tests. Treatment of early syphilis in HIV-positive patients has been associated with the early development of neurosyphilis. It is advisable to treat all patients co-infected with HIV with an antibiotic regimen that achieves adequate levels within the CSF.

Single-dose antibiotic therapy: what has the past taught us?

The proper dosage schedule of antibiotics has generally been determined empirically, due to the difficulty of clinical trials. Initially, the dosage was chosen to allow high sustained levels greater than MIC in the blood. Antibiotics (beta lactams, tetracyclins, macrolides) were given at high doses three to six times daily, whatever their kinetic properties. The data obtained by Eagle3 with beta lactams in animal models of streptococcal and treponemal infections outlined the importance of interval between doses on the in vivo efficacy. They also showed that increasing the dose of penicillin had a positive effect on the bactericidal activity only through the persistence of effective levels (greater than MIC) at the site of infection. Further illustrations were given through experimental and clinical studies with beta lactams or other compounds on different types of infections: LRTIs, UTIs, meningitis, and endocarditis. The importance of both dynamic (i.e., pattern of bactericidal effect) and kinetic (elimination half-life) parameters was thus further identified. Information on toxicity with some compounds with a narrow therapeutic index, such as aminoglycosides, indicated that increasing the dose to enhance efficacy had some limitations. This led to numerous studies on the relations between concentration and toxicity, stating that nephro- or ototoxicity were not directly related to peak level in serum. Experimental studies showed that OD administration of aminoglycosides was both more efficient and less toxic than the multiple-dose regimen of the same daily amount. Economic considerations progressively justified attempts to both reduce the dose and the work load related to multiple administrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-antibiotic effect of the new streptogramin RP 59500

The post-antibiotic effect (PAE) of RP 59500, a new streptogramin antibiotic, was determined for Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, Streptococcus pneumoniae, and Streptococcus pyogenes. A 30 min exposure of Staphylococcus aureus to 5 micrograms/ml of RP 59500 produced a PAE of 1.9-6.9 h, and a 60 min exposure of 2.5 micrograms/ml produced a PAE of 3.2-8 h. A 30 min exposure of 5 micrograms/ml of RP 59500 of coagulase-negative staphylococci produced a PAE of 2.5-7.5 h. PAEs of constitutively erythromycin-resistant staphylococcal isolates were shorter than were the PAEs of highly susceptible isolates. A 30 min exposure to 5 micrograms/ml of RP 59500 produced a PAE of 7.5-9.5 h for Streptococcus pneumoniae and a PAE of greater than 18 h for Streptococcus pyogenes. RP 59500 produced a longer PAE with Staphylococcus aureus than did vancomycin, oxacillin or erythromycin. These results suggest that RP 59500 may be administered less frequently than would be suggested by its half-life.

Antibiotic tissue penetration and its relevance: models of tissue penetration and their meaning

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