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

Pharmacokinetics of thymoquinone in layer chickens following oral and intravenous administration

Thymoquinone (TQ) is the major constituent of Nigella sativa and known to possess a variety of pharmacological effects. This study was designed to evaluate the pharmacokinetic profile of TQ following oral (PO) and intravenous (IV) administration in layer chickens. The layer chickens were equally divided into two groups (six chickens in each group, total 12 chickens), and TQ was administered via PO and IV routes. For PO route, the dose was 20 mg/kg b.w. and for IV route, 5 mg/kg b.w. was administered, respectively. A sensitive and accurate High-Performance Liquid Chromatography (HPLC) technique was validated for the quantification of TQ from plasma. The limit of detection (LOD) and limit of quantification (LOQ) were 0.02 µg/ml and 0.05 µg/ml, respectively with >80% recovery. Maximum plasma concentration (C_max ) following PO and IV administration was 8.805 and 4.497 µg/ml, respectively, while time to reach at maximum concentration (T_max ) was 1 and 0.1 hr, respectively. The elimination half-lives were recorded as 1.02 and 0.978 hr, whereas the mean residence times were 1.79 and 1.036 hr following both PO and IV administration, respectively. The 85% PO bioavailability was indicative that TQ could be used for various therapeutic purposes in layer chickens.

Urinary antibacterial activity of fosfomycin and nitrofurantoin at registered dosages in healthy volunteers

Given emerging uropathogen resistance to more recent antibiotics, old antibiotics used for uncomplicated urinary tract infection (UTI) warrant re-examination. In this study, the urinary antibacterial activities of fosfomycin and nitrofurantoin were investigated by determining the urinary inhibitory titre and urinary bactericidal titre against uropathogens in urine samples from female volunteers following administration of single-dose fosfomycin (3 g) or nitrofurantoin (50 mg q6h or 100 mg q8h). Urine samples were collected over 48 h (fosfomycin) or 6 or 8 h (nitrofurantoin), with drug levels quantified with every void. Fosfomycin concentrations ranged from <0.75 mg/L [lower limit of quantification (LLOQ)] to 5729.9 mg/L and nitrofurantoin concentrations ranged from <4 mg/L (LLOQ) to 176.3 mg/L (50 mg q6h) or 209.4 mg/L (100 mg q8h). There was discrepancy in the response to fosfomycin between Escherichia coli and Klebsiella pneumoniae, with fosfomycin displaying strong bactericidal activity for 48 h against E. coli but moderate bactericidal activity for 18 h against K. pneumoniae. This effect was not related to the strain's baseline minimum inhibitory concentration but rather to the presence of a resistant subpopulation. Maximum titres of nitrofurantoin were obtained during the first 2 h, but no antibacterial effect was found in most samples regardless of the dose. In the rare samples in which antibacterial activity was detectable, titres were comparable for both species tested. These findings confirm doubts regarding fosfomycin administration in UTIs caused by K. pneumoniae and reveal a discrepancy between nitrofurantoin's measurable ex vivo activity and its clinical effect over multiple dosing intervals.

Effects of i.v. push administration on β-lactam pharmacodynamics

PURPOSE

The effects of i.v. push administration on the pharmacodynamic exposures of meropenem, cefepime, and aztreonam were evaluated.

METHODS

Pharmacokinetic and pharmacodynamic analyses were conducted using previously published pharmacokinetic data for meropenem, cefepime, and aztreonam. The probability of target attainment (PTA) was assessed using Monte Carlo simulations for 30-minute and 5-minute infusions of approved dosing regimens and alternative dosing schemes often used in clinical practice, including 500 mg every 6 hours and 1 g every 8 hours for meropenem, 1 g every 6 hours and 2 g every 8 hours for cefepime, and 2 g every 8 hours for aztreonam. For each regimen examined, means and standard deviations for the percentage of the dosing interval that the free drug concentration remained above the minimum inhibitory concentration (MIC) were calculated and reported.

RESULTS

No or only minor differences were noted between 30-minute and 5-minute infusions. The largest differences were observed at an MIC of 4 mg/L for meropenem and an MIC of 16 mg/L for aztreonam. At an MIC of 4 mg/L, meropenem 500 mg every 6 hours as a 30-minute infusion had an 8% greater PTA compared with the 5-minute infusion. At an MIC of 16 mg/L, a 30-minute infusion of aztreonam 2 g every 8 hours had a 12% greater PTA compared with the 5-minute infusion.

CONCLUSION

Simulations of meropenem, cefepime, and aztreonam by i.v. push over 5 minutes indicated that there would be minimal or no effect on pharmacodynamic exposures compared with the effect when administered by 30-minute infusions.

Development and validation of a fast and sensitive UHPLC-DAD assay for the quantification of nitrofurantoin in plasma and urine

Nitrofurantoin is an antimicrobial drug that has been used in the treatment of lower urinary tract infections for more than 50 years. Despite its long use, surprisingly little is known of the pharmacokinetics of nitrofurantoin, whereas this is essential to optimize patient treatment. We developed a novel analytical method for the quantification of nitrofurantoin in plasma and urine using ultra-high performance liquid chromatography and diode array detection to allow pharmacokinetic studies in these two matrices. The sample preparation method consisted of protein precipitation for plasma and liquid-liquid extraction for urine. 100 μL was needed for the sample preparation. Furazolidone was used as internal standard. Gradient chromatographic separation was performed on a HSS-T3 column. UV detection was performed at a wavelength of 369 nm. The analysis time was 5 min. The method was successfully validated according to the FDA-guidelines (2018). Linearity was confirmed over a concentration range from 50 to 1250 μg/L in plasma and from 4 to 200 mg/L in urine (r² > 0.95). Validation results of five QC concentrations for plasma and urine, respectively, are for within-day accuracy <± 13% in both matrices, for between-day accuracy <± 7% and <± 9%, for within-day precision <10% and <4% and for between-day precision <10% and <5%. Plasma samples are stable for seven days at 4 °C, and for 2 years at -20 °C and-80 °C. Urine samples are stable for at least seven days at 4 °C and at room temperature and for 2 years at -20 °C andat -80 °C, except from the lower concentrated samples, which are only stable at -80 °C. All samples were kept from daylight using amber colored glassware. The presented method meets all validation requirements and was successfully used in a clinical study where the pharmacokinetics of nitrofurantoin were investigated in healthy volunteers. The easy sample preparation method and the short analysis time make this method suitable for use during routine clinical practice to study the pharmacokinetics of nitrofurantoin.

Development of a Minimally Invasive Microneedle-Based Sensor for Continuous Monitoring of β-Lactam Antibiotic Concentrations in Vivo

Antimicrobial resistance poses a global threat to patient health. Improving the use and effectiveness of antimicrobials is critical in addressing this issue. This includes optimizing the dose of antibiotic delivered to each individual. New sensing approaches that track antimicrobial concentration for each patient in real time could allow individualized drug dosing. This work presents a potentiometric microneedle-based biosensor to detect levels of β-lactam antibiotics in vivo in a healthy human volunteer. The biosensor is coated with a pH-sensitive iridium oxide layer, which detects changes in local pH as a result of β-lactam hydrolysis by β-lactamase immobilized on the electrode surface. Development and optimization of the biosensor coatings are presented, giving a limit of detection of 6.8 μM in 10 mM PBS solution. Biosensors were found to be stable for up to 2 weeks at -20 °C and to withstand sterilization. Sensitivity was retained after application for 6 h in vivo. Proof-of-concept results are presented showing that penicillin concentrations measured using the microneedle-based biosensor track those measured using both discrete blood and microdialysis sampling in vivo. These preliminary results show the potential of this microneedle-based biosensor to provide a minimally invasive means to measure real-time β-lactam concentrations in vivo, representing an important first step toward a closed-loop therapeutic drug monitoring system.

Therapeutic Drug Monitoring of Beta-Lactams and Other Antibiotics in the Intensive Care Unit: Which Agents, Which Patients and Which Infections?

Antibiotics are among the medications most frequently administered to the critically ill, a population with high levels of intra- and inter-individual pharmacokinetic variability. Our knowledge of the relationships among antibiotic dosing, exposure and clinical effect in this population has increased in recent decades. Therapeutic drug monitoring (TDM) of serum antibiotic concentrations is the most practical means of assessing adequate antibiotic exposure, though until recently, it has been underutilised for this end. Now TDM is becoming more widespread, particularly for the beta-lactam antibiotics, a class historically thought to have a wide therapeutic range. We review the basic requirements, indications, and targets for effective TDM of the glycopeptides, aminoglycosides, quinolones and beta-lactam antibiotics in the adult intensive-care setting, with a special focus on TDM of the beta-lactam antibiotics, the most widely used antibiotic class.

Optimizing dosing of nitrofurantoin from a PK/PD point of view: What do we need to know?

Nitrofurantoin is an old antibiotic and an important first-line oral antibiotic for the treatment of uncomplicated urinary tract infections. However despite its long term use for over 60 years, little information is available with respect to its dose justification and this may be the reason of highly variable recommended doses and dosing schedules. Furthermore, nitrofurantoin is not a uniform product -crystal sizes of nitrofurantoin, and therefore pharmacokinetic properties, differ significantly by product. Moreover, pharmacokinetic profiling of some products is even lacking, or difficult to interpret because of its unstable chemical properties. Pharmacokinetic and pharmacodynamic data is now slowly becoming available. This review provides an overview of nitrofurantoins antibacterial, pharmacokinetic and pharmacodynamic properties. This shows that a clear rationale of current dosing regimens is scanty.

Evolutionary epidemiology models to predict the dynamics of antibiotic resistance

The evolution of resistance to antibiotics is a major public health problem and an example of rapid adaptation under natural selection by antibiotics. The dynamics of antibiotic resistance within and between hosts can be understood in the light of mathematical models that describe the epidemiology and evolution of the bacterial population. "Between-host" models describe the spread of resistance in the host community, and in more specific settings such as hospitalized hosts (treated by antibiotics at a high rate), or farm animals. These models make predictions on the best strategies to limit the spread of resistance, such as reducing transmission or adapting the prescription of several antibiotics. Models can be fitted to epidemiological data in the context of intensive care units or hospitals to predict the impact of interventions on resistance. It has proven harder to explain the dynamics of resistance in the community at large, in particular because models often do not reproduce the observed coexistence of drug-sensitive and drug-resistant strains. "Within-host" models describe the evolution of resistance within the treated host. They show that the risk of resistance emergence is maximal at an intermediate antibiotic dose, and some models successfully explain experimental data. New models that include the complex host population structure, the interaction between resistance-determining loci and other loci, or integrating the within- and between-host levels will allow better interpretation of epidemiological and genomic data from common pathogens and better prediction of the evolution of resistance.

Highly variable absorption of clavulanic acid during the day: a population pharmacokinetic analysis

Objectives

To calculate the clavulanic acid exposure of oral amoxicillin/clavulanic acid dosing regimens, to investigate variability using a population pharmacokinetic model and to explore target attainment using Monte Carlo simulations.

Methods

Two groups of healthy male volunteers received amoxicillin/clavulanic acid tablets at the start of a standard meal on two separate days 1 week apart. One group (n = 14) received 875/125 mg q12h and 500/125 mg q8h and the other group (n = 15) received 500/125 mg q12h and 250/125 mg q8h. In total, 1479 blood samples were collected until 8-12 h after administration. Concentrations were analysed using non-compartmental (WinNonLin) and population pharmacokinetic (NONMEM) methods.

Results

Median Cmax and AUC0-8 were 2.21 mg/L (0.21-4.35) and 4.99 mg·h/L (0.44-8.31), respectively. In 40/58 daily concentration-time profiles, Cmax and AUC0-8 of the morning dose were higher than with later doses. The final population model included a lag time (0.447 h), first-order absorption (3.99 h-1 at 8:00 h, between-subject variability 52.8%, between-occasion variability 48.5%), one distribution compartment (33.0 L, between-subject variability 23.9%) and first-order elimination (24.6 L/h, between-subject variability 26.7%). Bioavailability (fixed at 1 at 8:00 h, between-occasion variability 28.2%) and absorption rate decreased over the day. For 97.5% of the simulated population after 125 mg q12h or q8h, %fT > Ct at 0.5 mg/L was 8.33% (q12h) and 15.2% (q8h), %fT > Ct at 1 mg/L was 0% (q12h + q8h), and fAUC0-24 was 3.61 (q12h) and 5.56 (q8h)  mg·h/L.

Conclusions

Clavulanic acid absorption in healthy volunteers is highly variable. Bioavailability and absorption rate decrease over the day. The model developed here may serve to suggest clavulanic acid dosing regimens to optimize efficacy and prevent underdosing.

Intravenous fosfomycin for the treatment of multidrug-resistant pathogens: what is the evidence on dosing regimens?

INTRODUCTION

The intravenous (IV) formulation of fosfomycin has been re-introduced in clinical practice mainly to overcome treatment failures against multidrug-resistant (MDR) bacteria. Appropriate dosing schedules of the IV formulation have not yet been established. Areas covered: The mechanism of action and resistance development, commercial IV formulations, pharmacokinetic/pharmacodynamic (PK/PD) properties, IV dosing regimens for the treatment of MDR infections along with efficacy and safety issues were reviewed. Data regarding specific MDR pathogens, daily doses and patients' outcomes, gaps in the current literature, and in progress research agenda are presented. Expert opinion: The doses of fosfomycin IV range between 12 and 24 grams/day depending on the severity of infection. The efficacy and safety of the commonly administered doses have been shown mainly in observational non-comparative trials. The optimal dose ensuring maximal efficacy with minimal toxicity along with the most appropriate co-administered antibiotic(s) need further evaluation. The pharmacokinetic/pharmacodynamic parameter associated with maximum efficacy has not yet been established, although, the ratio of the area under the concentration-time curve (AUC) for the free unbound fraction of fosfomycin versus the MIC (fAUC/MIC) may be linked to optimal treatment. RCTs and other comparative studies are underway to address gaps of knowledge in adult patients and neonates.

In vivo pharmacokinetic/Pharmacodynamic modeling of Enrofloxacin against Escherichia coli in broiler chickens

Background

Systemic Escherichia coli infections cause early mortality of commercial broiler chickens. Although enrofloxacin has long been used in poultry, the in vivo pharmacokinetic/pharmacodynamic (PK/PD) relationship of enrofloxacin against E. coli is unclear. The present study aimed to establish an in vivo PK/PD model of enrofloxacin against E. coli in seven-day-old chicks and to ascertain whether the selection of target organ for PD determination is critical for parameter magnitude calculation in enrofloxacin PK/PD modeling.

Results

The in vivo effectiveness of enrofloxacin against E. coli in different organs varied, with the E_max ranging from − 4.4 to − 5.8 Log₁₀ colony forming units (cfu)/mL or cfu/g. Both the surrogate AUC_0–24/MIC of enrofloxacin or AUC_0–24/MIC of the combination of enrofloxacin and ciprofloxacin correlated well with effectiveness in each organ. The AUC_0–24/MIC ratio of the combination of enrofloxacin and ciprofloxacin producing bactericidal and elimination effects were 21.29 and 32.13 in blood; 41.68, and 58.52 in the liver; and 27.65 and 46.22 in the lung, respectively.

Conclusions

The in vivo effectiveness of enrofloxacin against E. coli in different organs was not identical after administration of the same dosage. To describe the magnitude of PK/PD parameter exactly, bacterial loading reduction in different organs as PD endpoints should be evaluated and compared in PK/PD modeling. The selection of a target organ to evaluate PDs is critical for rational dosage recommendation.

Validation of a Dried Blood Spot Ceftriaxone Assay in Papua New Guinean Children with Severe Bacterial Infections

Dried blood spot (DBS) antibiotic assays can facilitate pharmacokinetic (PK) studies in situations where venous blood sampling is logistically and/or ethically challenging. In this study, we aimed to demonstrate the validity of a DBS ceftriaxone assay in a PK study of children with severe illness from Papua New Guinea (PNG), a setting in which health care resources are limited and anemia is common. Using a previously validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay, serial plasma and DBS ceftriaxone concentrations were measured in PNG children aged 5 to 10 years with acute bacterial meningitis or severe pneumonia. The concentration-time data were incorporated into population PK models. Ten children were recruited with an admission hematocrit of 0.22 to 0.52. Raw data demonstrated good correlation between plasma and DBS concentrations (Spearman's rank correlation coefficient [r_s] = 0.94 [95% confidence interval, 0.91 to 0.97], P < 0.0001). A marked systematic hematocrit bias was observed, with lower hematocrits resulting in underestimation of DBS-predicted plasma concentration. After adjustment for red cell partitioning and hematocrit bias, a population PK model comparing plasma and DBS-predicted plasma concentrations did not differ in terms of key PK parameters, including clearance, volume of distribution, and residual variability. The performance of the ceftriaxone DBS assay is robust and provides reassurance that this platform can be used as a surrogate for plasma concentrations to provide valid PK and PK/pharmacodynamic studies of severely unwell children hospitalized in a resource-limited setting. It highlights the importance of hematocrit bias in validation studies of DBS assays.

Population Pharmacokinetic Study of Amoxicillin-Treated Burn Patients Hospitalized at a Swiss Tertiary-Care Center

The objective of this study was to investigate the population pharmacokinetics (PK) of amoxicillin in ICU burn patients and the optimal dosage regimens. This was a prospective study involving 21 consecutive burn patients receiving amoxicillin. PK data were analyzed using nonlinear mixed-effects modeling. Monte-Carlo simulations assessed the influence of various amoxicillin dosage regimens with identified covariates on the probability to achieve a target (PTA) value of time during which free amoxicillin concentrations in plasma exceeded the MIC (fT>MIC). A two-compartment model best described the data. Creatinine clearance (CL_CR) and body weight (BW) influenced amoxicillin CL and central volume of distribution (V₁), respectively. The median CL_CR (Cockcroft-Gault formula) was high (128 ml/min), with 25% of patients having CL_CRs of >150 ml/min. The CL, V₁, and half-life (t_1/2) values at steady state for a patient with a CL_CR of 110 ml/min and BW of 70 kg were 13.6 liters/h, 9.7 liters, and 0.8 h, respectively. Simulations showed that a target fT>MIC of ≥50% was achieved (PTA > 90%) with standard amoxicillin dosage regimens (1 to 2 g every 6 to 8 h [q6-8h]) when the MIC was low (<1 mg/liter). However, increased dosages of up to 2 g/4 h were necessary in patients with augmented CL_Rs or higher MICs. Prolonging amoxicillin infusion from 30 min to 2 h had a favorable effect on target attainment. In conclusion, this population analysis shows an increased amoxicillin CL and substantial CL PK variability in burn patients compared to literature data with nonburn patients. Situations of augmented CL_CR and/or high bacterial MIC target values may require dosage increases and longer infusion durations. (This study has been registered at ClinicalTrials.gov under identifier NCT01965340.).

[Bacterial sepsis : Diagnostics and calculated antibiotic therapy]

The mortality of patients with sepsis and septic shock is still unacceptably high. An effective antibiotic treatment within 1 h of recognition of sepsis is an important target of sepsis treatment. Delays lead to an increase in mortality; therefore, structured treatment concepts form a rational foundation, taking relevant diagnostic and treatment steps into consideration. In addition to the assumed focus and individual risks of each patient, local resistance patterns and specific problem pathogens must be taken into account for selection of anti-infection treatment. Many pathophysiological alterations influence the pharmacokinetics of antibiotics during sepsis. The principle of standard dosing should be abandoned and replaced by an individual treatment approach with stronger weighting of the pharmacokinetics/pharmacodynamics (PK/PD) index of the substance groups. Although this is not yet the clinical standard, prolonged (or continuous) infusion of beta-lactam antibiotics and therapeutic drug monitoring (TDM) can help to achieve defined PK targets. Prolonged infusion is sufficient without TDM but for continuous infusion TDM is basically necessary. A further argument for individual PK/PD-oriented antibiotic approaches is the increasing number of infections due to multidrug resistant pathogens (MDR) in the intensive care unit. For effective treatment antibiotic stewardship teams (ABS team) are becoming more established. Interdisciplinary cooperation of the ABS team with infectiologists, microbiologists and clinical pharmacists leads not only to a rational administration of antibiotics but also has a positive influence on the outcome. The gold standards for pathogen detection are still culture-based detection and microbiological resistance testing for the various antibiotic groups. Despite the rapid investigation time, novel polymerase chain reaction (PCR)-based procedures for pathogen identification and resistance determination, are currently only an adjunct to routine sepsis diagnostics due to the limited number of studies, high costs and limited availability. In complicated septic courses with multiple anti-infective treatment or recurrent sepsis, PCR-based procedures can be used in addition to therapy monitoring and diagnostics. Novel antibiotics represent potent alternatives in the treatment of MDR infections. Due to the often defined spectrum of pathogens and the practically absent resistance, they are suitable for targeted treatment of severe MDR infections (therapy escalation).

Clinical applications of population pharmacokinetic models of antibiotics: Challenges and perspectives

Because of increasing antimicrobial resistance and the shortage of new antibiotics, there is a growing need to optimize the use of old and new antibiotics. Modelling of the pharmacokinetic/pharmacodynamic (PK/PD) characteristics of antibiotics can support the optimization of dosing regimens. Antimicrobial efficacy is determined by susceptibility of the drug to the microorganism and exposure to the drug, which relies on the PK and the dose. Population PK models describe relationships between patients characteristics and drug exposure. This article highlights three clinical applications of these models applied to antibiotics: 1) dosing evaluation of old antibiotics, 2) setting clinical breakpoints and 3) dosing individualization using therapeutic drug monitoring (TDM). For each clinical application, challenges regarding interpretation are discussed. An important challenge is to improve the understanding of the interpretation of modelling results for good implementation of the dosing recommendations, clinical breakpoints and TDM advices. Therefore, also background information on PK/PD principles and approaches to analyse PK/PD data are provided.

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.

Optimization of Antimicrobial Treatment to Minimize Resistance Selection

Optimization of antimicrobial treatment is a cornerstone in the fight against antimicrobial resistance. Various national and international authorities and professional veterinary and farming associations have released generic guidelines on prudent antimicrobial use in animals. However, these generic guidelines need to be translated into a set of animal species- and disease-specific practice recommendations. This article focuses on prevention of antimicrobial resistance and its complex relationship with treatment efficacy, highlighting key situations where the current antimicrobial drug products, treatment recommendations, and practices may be insufficient to minimize antimicrobial selection. The authors address this topic using a multidisciplinary approach involving microbiology, pharmacology, clinical medicine, and animal husbandry. In the first part of the article, we define four key targets for implementing the concept of optimal antimicrobial treatment in veterinary practice: (i) reduction of overall antimicrobial consumption, (ii) improved use of diagnostic testing, (iii) prudent use of second-line, critically important antimicrobials, and (iv) optimization of dosage regimens. In the second part, we provided practice recommendations for achieving these four targets, with reference to specific conditions that account for most antimicrobial use in pigs (intestinal and respiratory disease), cattle (respiratory disease and mastitis), dogs and cats (skin, intestinal, genitourinary, and respiratory disease), and horses (upper respiratory disease, neonatal foal care, and surgical infections). Lastly, we present perspectives on the education and research needs for improving antimicrobial use in the future.

Effect of outpatient antibiotics for urinary tract infections on antimicrobial resistance among commensal Enterobacteriaceae: a multinational prospective cohort study

OBJECTIVES

We quantified the impact of antibiotics prescribed in primary care for urinary tract infections (UTIs) on intestinal colonization by ciprofloxacin-resistant (CIP-RE) and extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-PE), while accounting for household clustering.

METHODS

Prospective cohort study from January 2011 to August 2013 at primary care sites in Belgium, Poland and Switzerland. We recruited outpatients requiring antibiotics for suspected UTIs or asymptomatic bacteriuria (exposed patients), outpatients not requiring antibiotics (non-exposed patients), and one to three household contacts for each patient. Faecal samples were tested for CIP-RE, ESBL-PE, nitrofurantoin-resistant Enterobacteriaceae (NIT-RE) and any Enterobacteriaceae at baseline (S1), end of antibiotics (S2) and 28 days after S2 (S3).

RESULTS

We included 300 households (205 exposed, 95 non-exposed) with 716 participants. Most exposed patients received nitrofurans (86; 42%) or fluoroquinolones (76; 37%). CIP-RE were identified in 16% (328/2033) of samples from 202 (28%) participants. Fluoroquinolone treatment caused transient suppression of Enterobacteriaceae (S2) and subsequent two-fold increase in CIP-RE prevalence at S3 (adjusted prevalence ratio (aPR) 2.0, 95% CI 1.2-3.4), with corresponding number-needed-to-harm of 12. Nitrofurans had no impact on CIP-RE (aPR 1.0, 95% CI 0.5-1.8) or NIT-RE. ESBL-PE were identified in 5% (107/2058) of samples from 71 (10%) participants, with colonization not associated with antibiotic exposure. Household exposure to CIP-RE or ESBL-PE was associated with increased individual risk of colonization: aPR 1.8 (95% CI 1.3-2.5) and 3.4 (95% CI 1.3-9.0), respectively.

CONCLUSIONS

These findings support avoidance of fluoroquinolones for first-line UTI therapy in primary care, and suggest potential for interventions that interrupt household circulation of resistant Enterobacteriaceae.

Fosfomycin: Pharmacological, Clinical and Future Perspectives

Fosfomycin is a bactericidal, low-molecular weight, broad-spectrum antibiotic, with putative activity against several bacteria, including multidrug-resistant Gram-negative bacteria, by irreversibly inhibiting an early stage in cell wall synthesis. Evidence suggests that fosfomycin has a synergistic effect when used in combination with other antimicrobial agents that act via a different mechanism of action, thereby allowing for reduced dosages and lower toxicity. Fosfomycin does not bind to plasma proteins and is cleared via the kidneys. Due to its extensive tissue penetration, fosfomycin may be indicated for infections of the CNS, soft tissues, bone, lungs, and abscesses. The oral bioavailability of fosfomycin tromethamine is <50%; therefore, oral administration of fosfomycin tromethamine is approved only as a 3-gram one-time dose for treating urinary tract infections. However, based on published PK parameters, PK/PD simulations have been performed for several multiple-dose regimens, which might lead to the future use of fosfomycin for treating complicated infections with multidrug-resistant bacteria. Because essential pharmacological information and knowledge regarding mechanisms of resistance are currently limited and/or controversial, further studies are urgently needed, and fosfomycin monotherapy should be avoided.

Reducing Antibacterial Development Risk for GSK1322322 by Exploring Potential Human Dose Regimens in Nonclinical Efficacy Studies Using Immunocompetent Rats

Directly testing proposed clinical dosing regimens in nonclinical studies can reduce the risk during the development of novel antibacterial agents. Optimal dosing regimens can be identified in animal models by testing recreated human pharmacokinetic profiles. An example of this approach using continuous intravenous infusions of GSK1322322 in immunocompetent rats to evaluate recreated human exposures from phase I trials in pneumonia models with Streptococcus pneumoniae and Haemophilus influenzae and an abscess model with Staphylococcus aureus is presented. GSK1322322 was administered via continuous intravenous infusion to recreate 1,000- or 1,500-mg oral doses every 12 h in humans. Significant reductions (P ≤ 0.05 for all comparisons) in bacterial numbers compared with those for the baseline controls were observed for S. pneumoniae and H. influenzae (mean log₁₀ reductions, 1.6 to ≥2.7 and 1.8 to 3.3 CFU/lungs, respectively) with the recreated 1,000-mg oral dose. This profile was also efficacious against S. aureus (mean log₁₀ reduction, 1.9 to 2.4 CFU/abscess). There was a nonsignificant trend for improved efficacy against S. aureus with the 1,500-mg oral dose (mean log₁₀ reduction, 2.4 to 3.1 CFU/abscess). These results demonstrate that the human oral 1,000- or 1,500-mg exposure profiles of GSK1322322 recreated in rats were effective against representative community-associated pathogens and supported selection of the 1,500-mg oral dose given every 12 h for a phase II clinical skin infection study. Furthermore, this work exemplifies how the testing of recreated human pharmacokinetic profiles can be incorporated into the development process and serve as an aid for selecting optimal dosing regimens prior to conducting large-scale clinical studies.

Exploiting ecology in drug pulse sequences in favour of population reduction

A deterministic population dynamics model involving birth and death for a two-species system, comprising a wild-type and more resistant species competing via logistic growth, is subjected to two distinct stress environments designed to mimic those that would typically be induced by temporal variation in the concentration of a drug (antibiotic or chemotherapeutic) as it permeates through the population and is progressively degraded. Different treatment regimes, involving single or periodical doses, are evaluated in terms of the minimal population size (a measure of the extinction probability), and the population composition (a measure of the selection pressure for resistance or tolerance during the treatment). We show that there exist timescales over which the low-stress regime is as effective as the high-stress regime, due to the competition between the two species. For multiple periodic treatments, competition can ensure that the minimal population size is attained during the first pulse when the high-stress regime is short, which implies that a single short pulse can be more effective than a more protracted regime. Our results suggest that when the duration of the high-stress environment is restricted, a treatment with one or multiple shorter pulses can produce better outcomes than a single long treatment. If ecological competition is to be exploited for treatments, it is crucial to determine these timescales, and estimate for the minimal population threshold that suffices for extinction. These parameters can be quantified by experiment.

High interindividual variability in urinary fosfomycin concentrations in healthy female volunteers

OBJECTIVES

Fosfomycin is increasingly being prescribed for treatment of uncomplicated urinary tract infections in an era of emerging drug resistance. Surprisingly, little is known of the urinary concentrations of fosfomycin and its interindividual variation after the standard single 3-g oral dose. We aimed to gain more insight into urinary fosfomycin pharmacokinetics to evaluate its effectiveness.

METHODS

Three grams of fosfomycin trometamol was administered to 40 healthy female volunteers with an estimated mean glomerular filtration rate of >90 mL/min/1.73m². Urine samples were collected from every urination during 48 hours, and then twice daily for up to 7 days. Time, volume, and pH were recorded. Concentrations were quantified with UPLC-MS/MS. Effectiveness was evaluated based on urinary concentrations and the target MIC of E. coli, the most common uropathogen.

RESULTS

A high interindividual variability was found. Peak concentration was 1982.0 ± 1257.4 mg/L, urinary half-life 12.4 ± 5.7 hours, and excretion rate over 48 hours 29.9 ± 7.1 mg/h. Recovery was 44.5 ± 12.6% after 48 hours and 47.0 ± 10.4% after 7 days. Concentrations remained above the EUCAST breakpoint of 32 mg/L in 100% of the volunteers over the first 24 hours, 67.5% for 48 hours, and 30% for 72 hours. A high urinary output was associated with low urinary concentrations and consequently reduced time > MIC, AUC_0-7days/MIC, and C_max/MIC values.

CONCLUSIONS

Considerable interindividual variability observed in the pharmacokinetics of fosfomycin signifies a risk for inadequate drug exposure in a significant proportion of the population. The current dosing regimen should therefore be reevaluated.

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.

Pharmacokinetic-pharmacodynamic integration and modelling of oxytetracycline for the calf pathogens Mannheimia haemolytica and Pasteurella multocida

A calf tissue cage model was used to study the pharmacokinetics (PK) and pharmacodynamics (PD) of oxytetracycline in serum, inflamed (exudate) and noninflamed (transudate) tissue cage fluids. After intramuscular administration, the PK was characterized by a long mean residence time of 28.3 hr. Based on minimum inhibitory concentrations (MICs) for six isolates each of Mannheimia haemolytica and Pasteurella multocida, measured in serum, integration of in vivo PK and in vitro PD data established area under serum concentration-time curve (AUC_0-∞ )/MIC ratios of 30.0 and 24.3 hr for M. haemolytica and P. multocida, respectively. Corresponding AUC_0-∞ /MIC ratios based on MICs in broth were 656 and 745 hr, respectively. PK-PD modelling of in vitro bacterial time-kill curves for oxytetracycline in serum established mean AUC_0-24 hr /MIC ratios for 3log₁₀ decrease in bacterial count of 27.5 hr (M. haemolytica) and 60.9 hr (P. multocida). Monte Carlo simulations predicted target attainment rate (TAR) dosages. Based on the potency of oxytetracycline in serum, the predicted 50% TAR single doses required to achieve a bacteriostatic action covering 48-hr periods were 197 mg/kg (M. haemolytica) and 314 mg/kg (P. multocida), respectively, against susceptible populations. Dosages based on the potency of oxytetracycline in broth were 25- and 27-fold lower (7.8 and 11.5 mg/kg) for M. haemolytica and P. multocida, respectively.

Prediction of marbofloxacin dosage for the pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida by pharmacokinetic/pharmacodynamic modelling

Background

Bacterial pneumonia in pigs occurs widely and requires antimicrobial therapy. It is commonly caused by the pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida. Marbofloxacin is an antimicrobial drug of the fluoroquinolone class, licensed for use against these organisms in the pig. In recent years there have been major developments in dosage schedule design, based on integration and modelling of pharmacokinetic (PK) and pharmacodynamic (PD) data, with the objective of optimising efficacy and minimising the emergence of resistance. From in vitro time-kill curves in pig serum, PK/PD breakpoint Area under the curve (AUC) _24h /minimum inhibitory concentration (MIC) values were determined and used in conjunction with published PK, serum protein binding data and MIC distributions to predict dosages based on Monte Carlo simulation (MCS).

Results

For three levels of inhibition of growth, bacteriostasis and 3 and 4log₁₀ reductions in bacterial count, mean AUC_24h/MIC values were 20.9, 45.2 and 71.7 h, respectively, for P. multocida and 32.4, 48.7 and 55.5 h for A. pleuropneumoniae. Based on these breakpoint values, doses for each pathogen were predicted for several clinical scenarios: (1) bacteriostatic and bactericidal levels of kill; (2) 50 and 90% target attainment rates (TAR); and (3) single dosing and daily dosing at steady state. MCS for 90% TAR predicted single doses to achieve bacteriostatic and bactericidal actions over 48 h of 0.44 and 0.95 mg/kg (P. multocida) and 0.28 and 0.66 mg/kg (A. pleuropneumoniae). For daily doses at steady state, and 90% TAR bacteriostatic and bactericidal actions, dosages of 0.28 and 0.59 mg/kg (P. multocida) and 0.22 and 0.39 mg/kg (A. pleuropneumoniae) were required for pigs aged 12 weeks. Doses were also predicted for pigs aged 16 and 27 weeks.

Conclusions

PK/PD modelling with MCS approaches to dose determination demonstrates the possibility of tailoring clinical dose rates to a range of bacterial kill end-points.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1128-y) contains supplementary material, which is available to authorized users.

Antimicrobial Activity and Resistance: Influencing Factors

Rational use of antibiotic is the key approach to improve the antibiotic performance and tackling of the antimicrobial resistance. The efficacy of antimicrobials are influenced by many factors: (1) bacterial status (susceptibility and resistance, tolerance, persistence, biofilm) and inoculum size; (2) antimicrobial concentrations [mutant selection window (MSW) and sub-inhibitory concentration]; (3) host factors (serum effect and impact on gut micro-biota). Additional understandings regarding the linkage between antimicrobial usages, bacterial status and host response offers us new insights and encourage the struggle for the designing of antimicrobial treatment regimens that reaching better clinical outcome and minimizing the emergence of resistance at the same time.

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.

Cost-Effectiveness Analysis of Fosfomycin for Treatment of Uncomplicated Urinary Tract Infections in Ontario

Background and Objective. Bacterial resistance to antibiotics traditionally used to treat uncomplicated urinary tract infections (uUTIs) is rising in Canada. We compared the cost-per-patient in Ontario of including fosfomycin (an antibiotic with a low resistance profile) as an option for first-line empirical treatment of uUTIs with current cost of treatment with sulfonamides, fluoroquinolones, and nitrofurantoin. Methods. A decision-tree model was used to perform a cost-minimization analysis. All possible outcomes of a uUTI caused by bacterial species treated with either sulfonamides, fluoroquinolones, nitrofurantoin, or fosfomycin were included. Results. In the base case analysis, the cost-per-patient for treating uUTI with fosfomycin was $105.12. This is similar to the cost-per-patient for each of the other currently reimbursed antibiotics (e.g., $96.19 for sulfonamides, $98.85 for fluoroquinolones, and $99.09 for nitrofurantoins). The weighted average cost-per-patient for treating uUTI was not substantially elevated with the inclusion of fosfomycin in the treatment landscape ($98.41 versus $98.29 with and without fosfomycin, resp.). The sensitivity analyses revealed that most (88.34%) of the potential variation in cost was associated with the probability of progressing to pyelonephritis and hospitalization for pyelonephritis. Conclusion. Fosfomycin in addition to being a safe and effective agent to treat uUTI has a low resistance profile, offers a single-dose treatment administration, and is similar in cost to other reimbursed antibiotics.

Pharmacokinetic/pharmacodynamic integration and modelling of oxytetracycline for the porcine pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida

Pharmacokinetic–pharmacodynamic (PK/PD) integration and modelling were used to predict dosage schedules of oxytetracycline for two pig pneumonia pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) were determined in broth and porcine serum. PK/PD integration established ratios of average concentration over 48 h (C_av0–48 h)/MIC of 5.87 and 0.27 μg/mL (P. multocida) and 0.70 and 0.85 μg/mL (A. pleuropneumoniae) for broth and serum MICs, respectively. PK/PD modelling of in vitro time–kill curves established broth and serum breakpoint values for area under curve (AUC_0–24 h)/MIC for three levels of inhibition of growth, bacteriostasis and 3 and 4 log₁₀ reductions in bacterial count. Doses were then predicted for each pathogen, based on Monte Carlo simulations, for: (i) bacteriostatic and bactericidal levels of kill; (ii) 50% and 90% target attainment rates (TAR); and (iii) single dosing and daily dosing at steady‐state. For 90% TAR, predicted daily doses at steady‐state for bactericidal actions were 1123 mg/kg (P. multocida) and 43 mg/kg (A. pleuropneumoniae) based on serum MICs. Lower TARs were predicted from broth MIC data; corresponding dose estimates were 95 mg/kg (P. multocida) and 34 mg/kg (A. pleuropneumoniae).

Using Chemical Reaction Kinetics to Predict Optimal Antibiotic Treatment Strategies

Identifying optimal dosing of antibiotics has proven challenging-some antibiotics are most effective when they are administered periodically at high doses, while others work best when minimizing concentration fluctuations. Mechanistic explanations for why antibiotics differ in their optimal dosing are lacking, limiting our ability to predict optimal therapy and leading to long and costly experiments. We use mathematical models that describe both bacterial growth and intracellular antibiotic-target binding to investigate the effects of fluctuating antibiotic concentrations on individual bacterial cells and bacterial populations. We show that physicochemical parameters, e.g. the rate of drug transmembrane diffusion and the antibiotic-target complex half-life are sufficient to explain which treatment strategy is most effective. If the drug-target complex dissociates rapidly, the antibiotic must be kept constantly at a concentration that prevents bacterial replication. If antibiotics cross bacterial cell envelopes slowly to reach their target, there is a delay in the onset of action that may be reduced by increasing initial antibiotic concentration. Finally, slow drug-target dissociation and slow diffusion out of cells act to prolong antibiotic effects, thereby allowing for less frequent dosing. Our model can be used as a tool in the rational design of treatment for bacterial infections. It is easily adaptable to other biological systems, e.g. HIV, malaria and cancer, where the effects of physiological fluctuations of drug concentration are also poorly understood.

Potency of marbofloxacin for pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida: Comparison of growth media

Pharmacodynamic properties of marbofloxacin were established for six isolates each of the pig respiratory tract pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida. Three in vitro indices of potency were determined; Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Mutant Prevention Concentration (MPC). For MIC determination Clinical Laboratory Standards Institute guidelines were modified in three respects: (1) comparison was made between two growth media, an artificial broth and pig serum; (2) a high inoculum count was used to simulate heavy clinical bacteriological loads; and (3) five overlapping sets of two-fold dilutions were used to improve accuracy of determinations. Similar methods were used for MBC and MPC estimations. MIC and MPC serum:broth ratios for A. pleuropneumoniae were 0.79:1 and 0.99:1, respectively, and corresponding values for P. multocida were 1.12:1 and 1.32:1. Serum protein binding of marbofloxacin was 49%, so that fraction unbound (fu) serum MIC values were significantly lower than those predicted by correction for protein binding; fu serum:broth MIC ratios were 0.40:1 (A. pleuropneumoniae) and 0.50:1 (P. multocida). For broth, MPC:MIC ratios were 13.7:1 (A. pleuropneumoniae) and 14.2:1 (P. multocida). Corresponding ratios for serum were similar, 17.2:1 and 18.8:1, respectively. It is suggested that, for dose prediction purposes, serum data might be preferable to potency indices measured in broths.

[Pharmacokinetics and pharmacodynamics of antibiotics in intensive care]

Optimized dosage regimens of antibiotics have remained obscure since their introduction. During the last two decades pharmacokinetic(PK)-pharmacodynamic(PD) relationships, originally established in animal experiments, have been increasingly used in patients. The action of betalactams is believed to be governed by the time the plasma concentration is above the minimum inhibitory concentration (MIC). Aminoglycosides act as planned when the peak concentration is a multiple of the MIC and vancomycin seems to work best when the area under the plasma vs. time curve (AUC) to MIC has a certain ratio. Clinicians should be aware that these relationships can only be an indication in which direction dosing should go. Larger studies with sufficiently high numbers of patients and particularly severely sick patients are needed to prove the concepts. In times where all antibiotics can be measured with new technologies, the introduction of therapeutic drug monitoring (TDM) is suggested for ICUs (Intensive Care Unit). The idea of a central lab for TDM of antibiotics such as PEAK (Paul Ehrlich Antibiotika Konzentrationsmessung) is supported.

Linezolid in the treatment of drug-resistant tuberculosis: the challenge of its narrow therapeutic index

INTRODUCTION

Linezolid is an oxazolidinone with potent activity against M tuberculosis, and improves culture conversion and cure rates when added to treatment regimens for drug resistant tuberculosis. However, linezolid has a narrow therapeutic window, and the optimal dosing strategy that minimizes the substantial toxicity associated with linezolid's prolonged use in tuberculosis treatment has not been determined, limiting the potential impact of this anti-mycobacterial agent.

AREAS COVERED

This paper aims to review and summarize the current knowledge on linezolid for the treatment of drug-resistant tuberculosis. The focus is on the pharmacokinetic-pharmacodynamic determinants of linezolid's efficacy and toxicity in tuberculosis, and how this relates to defining an optimal dose. Mechanisms of linezolid toxicity and resistance, and the potential role of therapeutic drug monitoring are also covered. Expert commentary: Prospective pharmacokinetic-pharmacodynamic studies are required to define optimal therapeutic targets and to inform improved linezolid dosing strategies for drug-resistant tuberculosis.

Validation and Application of a Dried Blood Spot Assay for Biofilm-Active Antibiotics Commonly Used for Treatment of Prosthetic Implant Infections

Dried blood spot (DBS) antibiotic assays can facilitate pharmacokinetic (PK)/pharmacodynamic (PD) studies in situations where venous blood sampling is logistically difficult. We sought to develop, validate, and apply a DBS assay for rifampin (RIF), fusidic acid (FUS), and ciprofloxacin (CIP). These antibiotics are considered active against organisms in biofilms and are therefore commonly used for the treatment of infections associated with prosthetic implants. A liquid chromatography-mass spectroscopy DBS assay was developed and validated, including red cell partitioning and thermal stability for each drug and the rifampin metabolite desacetyl rifampin (Des-RIF). Plasma and DBS concentrations in 10 healthy adults were compared, and the concentration-time profiles were incorporated into population PK models. The limits of quantification for RIF, Des-RIF, CIP, and FUS in DBS were 15 μg/liter, 14 μg/liter, 25 μg/liter, and 153 μg/liter, respectively. Adjusting for hematocrit, red cell partitioning, and relative recovery, DBS-predicted plasma concentrations were comparable to measured plasma concentrations for each antibiotic (r > 0.95; P < 0.0001), and Bland-Altman plots showed no significant bias. The final population PK estimates of clearance, volume of distribution, and time above threshold MICs for measured and DBS-predicted plasma concentrations were comparable. These drugs were stable in DBSs for at least 10 days at room temperature and 1 month at 4°C. The present DBS antibiotic assays are robust and can be used as surrogates for plasma concentrations to provide valid PK and PK/PD data in a variety of clinical situations, including therapeutic drug monitoring or studies of implant infections.

[Dosing regimens of antibiotics in neonates: Variations in clinical practice and what should be done?]

There is wide variation in neonatal dosages of antibiotics in clinical practice, both nationally and internationally. This reflects the lack of evaluation of drugs in this therapeutic class, although widely prescribed. Given this situation, optimization of antibiotic prescription is required to ensure efficacy and safety of neonatal treatment and reduce microbial resistance. Rational prescription should be based on the knowledge of developmental pharmacokinetics and pharmacodynamics. Rigorous studies, conducted in collaboration between neonatologists and pharmacologists, are essential to develop and validate evidence-based neonatal dosage regimens.

Integrated pharmacokinetic-pharmacodynamic modelling to evaluate antimicrobial prophylaxis in abdominal surgery

OBJECTIVES

To use Monte Carlo simulation with an integrated pharmacokinetic-pharmacodynamic (PK-PD) model to evaluate guideline-recommended antimicrobial prophylaxis (AP) regimens with anaerobic coverage in abdominal surgery.

METHODS

AP regimens were tested in simulated subjects undergoing elective abdominal surgery using relevant PK models and pathogen distributions in surgical site infections (SSIs). Predicted cumulative target attainment was the percentage of simulated subjects with free (unbound) antimicrobial plasma concentrations above the MICs for potential SSI pathogens.

RESULTS

Cefazolin plus metronidazole covered SSI aerobes in 70% and the Bacteroides fragilis group in 99% of subjects, whereas cefoxitin only covered aerobes and anaerobes in 63% and 27% of cases, respectively. The broad-spectrum ceftriaxone plus metronidazole covered aerobes in 82% and anaerobes in 99% of simulations, while ertapenem covered aerobes in 88% and anaerobes in 90% of cases. Clindamycin covered the B. fragilis group in only 11% of cases. For cefazolin, 2 g doses maintained target attainment in simulated subjects from 80 to 120 kg, whereas 1 g doses were associated with lower target attainment against potential Gram-negative pathogens even in those <80 kg. For gentamicin, 3 mg/kg doses were comparable to the suggested 5 mg/kg, but superior to the traditional 1.5 mg/kg.

CONCLUSIONS

This study demonstrates the use of PK-PD to inform decisions regarding AP in abdominal surgery. In this case, the findings support avoiding cefoxitin, avoiding clindamycin for anaerobic coverage, selecting 2 g doses of cefazolin even in patients <80 kg and using 3 mg/kg doses of gentamicin.

Non-linear absorption pharmacokinetics of amoxicillin: consequences for dosing regimens and clinical breakpoints

OBJECTIVES

To describe the population pharmacokinetics of oral amoxicillin and to compare the PTA of current dosing regimens.

METHODS

Two groups, each with 14 healthy male volunteers, received oral amoxicillin/clavulanic acid tablets on two separate days 1 week apart. One group received 875/125 mg twice daily and 500/125 mg three times daily and the other group 500/125 mg twice daily and 250/125 mg three times daily. A total of 1428 amoxicillin blood samples were collected before and after administration. We analysed the concentration-time profiles using a non-compartmental pharmacokinetic method (PKSolver) and a population pharmacokinetic method (NONMEM). The PTA was computed using Monte Carlo simulations for several dosing regimens.

RESULTS

AUC0-24 and Cmax increased non-linearly with dose. The final model included the following components: Savic's transit compartment model, Michaelis-Menten absorption, two distribution compartments and first-order elimination. The mean central volume of distribution was 27.7 L and mean clearance was 21.3 L/h. We included variability for the central volume of distribution (34.4%), clearance (25.8%), transit compartment model parameters and Michaelis-Menten absorption parameters. For 40% fT>MIC and >97.5% PTA, the breakpoints were 0.125 mg/L (500 mg twice daily), 0.25 mg/L (250 mg three times daily and 875 mg twice daily), 0.5 mg/L (500 mg three times daily) and 1 mg/L (750, 875 or 1000 mg three times daily and 500 mg four times daily).

CONCLUSIONS

The amoxicillin absorption rate appears to be saturable. The PTAs of high-dose as well as twice-daily regimens are less favourable than regimens with lower doses and higher frequency.

Pharmacodynamics and differential activity of nitrofurantoin against ESBL-positive pathogens involved in urinary tract infections

BACKGROUND

Although nitrofurantoin has been used for >60 years for the treatment of uncomplicated urinary tract infections, its pharmacodynamic properties are not fully explored. Use is increasing because of increasing resistance to other antimicrobials due to ESBLs.

METHODS

We tested nine ESBL+ and two ESBL- strains in time-kill assays. Bactericidal activity and regrowth were assessed for all species and concentrations. Early-phase pharmacodynamics was analysed with a sigmoidal Emax model and the maximal killing rate, slope and EC50/MIC ratio were determined for each species.

RESULTS

A bactericidal effect was found at ≥2× MIC for Enterobacter cloacae after 4-8 h, for Klebsiella pneumoniae after 8-10 h and for Escherichia coli after 12-16 h. Overall, no killing was observed at low sub-MIC concentrations, whereas regrowth was found at 0.5-1× MIC after a short decline in cfu. The lowest maximal killing rates were observed for E. coli (0.21 ± 0.05 h(-1)), followed by K. pneumoniae (0.37 ± 0.09 h(-1)) and E. cloacae (0.87 ± 0.01 h(-1)). Surprisingly, the Hill slopes for these three species were significantly different (10.45 ± 9.37, 2.68 ± 0.64 and 1.01 ± 0.06, respectively), indicating a strong concentration-dependent early-phase antibacterial activity against E. cloacae. EC50/MIC ratios were significantly lower for E. coli (0.24 ± 0.08 mg/L) and K. pneumoniae (0.27 ± 0.03 mg/L) as compared with E. cloacae (0.77 ± 0.18 mg/L).

CONCLUSIONS

Nitrofurantoin was bactericidal against all species, demonstrating an unusual differential pattern of activity with concentration-dependent-type killing behaviour against E. cloacae and time-dependent killing behaviour against E. coli, which may have significant consequences on species-dependent dosing regimens. The results also demonstrate that the pharmacodynamic properties of some drugs cannot be generalized within a family, here the Enterobacteriaceae.

Clinically relevant concentrations of fosfomycin combined with polymyxin B, tobramycin or ciprofloxacin enhance bacterial killing of Pseudomonas aeruginosa, but do not suppress the emergence of fosfomycin resistance

OBJECTIVES

Fosfomycin resistance occurs rapidly with monotherapy. This study systematically investigated bacterial killing and emergence of fosfomycin resistance with fosfomycin combinations against Pseudomonas aeruginosa.

METHODS

Four clinical isolates and a reference strain of P. aeruginosa were employed. Combinations of fosfomycin plus polymyxin B, tobramycin or ciprofloxacin were examined over 24 h using time-kill studies (inocula ∼10(6) cfu/mL) incorporating clinically relevant concentrations (fosfomycin, 30, 150 or 300 mg/L; polymyxin B, 0.5, 1 or 2 mg/L; tobramycin, 0.5, 1.5 or 4 mg/L; ciprofloxacin, 0.5, 1 or 2.5 mg/L). Microbiological response was examined by log changes and population analysis profiles.

RESULTS

Against susceptible isolates, monotherapy produced varying degrees of initial killing followed by rapid regrowth. Fosfomycin plus polymyxin B or tobramycin produced greater initial killing (up to ∼4 log10 cfu/mL) with many concentrations compared with monotherapy against fosfomycin-susceptible (FOF(S)) isolates. With these combinations, synergy or additivity was observed in 54 (67%) and 49 (60%) of 81 cases (nine combinations across three isolates at three timepoints) for polymyxin B and tobramycin, respectively. Substantial improvements in killing were absent against fosfomycin-resistant (FOF(R)) isolates. For fosfomycin/ciprofloxacin combinations, synergy or additivity was observed against FOF(R) isolates in 33 of 54 (61%) cases (nine combinations across two isolates at three timepoints), while improvements in killing were largely absent against FOF(S) isolates. No combination prevented emergence of fosfomycin resistance.

CONCLUSIONS

Against P. aeruginosa, fosfomycin in combination with polymyxin B or tobramycin (FOF(S) isolates) or ciprofloxacin (FOF(R) isolates) increased bacterial killing, but did not suppress emergence of fosfomycin resistance.

Antimicrobial Drugs in Fighting against Antimicrobial Resistance

The outbreak of antimicrobial resistance, together with the lack of newly developed antimicrobial drugs, represents an alarming signal for both human and animal healthcare worldwide. Selection of rational dosage regimens for traditional antimicrobial drugs based on pharmacokinetic/pharmacodynamic principles as well as development of novel antimicrobials targeting new bacterial targets or resistance mechanisms are key approaches in tackling AMR. In addition to the cellular level resistance (i.e., mutation and horizontal gene transfer of resistance determinants), the community level resistance (i.e., bilofilms and persisters) is also an issue causing antimicrobial therapy difficulties. Therefore, anti-resistance and antibiofilm strategies have currently become research hotspot to combat antimicrobial resistance. Although metallic nanoparticles can both kill bacteria and inhibit biofilm formation, the toxicity is still a big challenge for their clinical applications. In conclusion, rational use of the existing antimicrobials and combinational use of new strategies fighting against antimicrobial resistance are powerful warranties to preserve potent antimicrobial drugs for both humans and animals.

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.

Pharmacodynamic modelling of in vitro activity of tetracycline against a representative, naturally occurring population of porcine Escherichia coli

Background

The complex relationship between drug concentrations and bacterial growth rates require not only the minimum inhibitory concentration but also other parameters to capture the dynamic nature of the relationship. To analyse this relationship between tetracycline concentration and growth of Escherichia coli representative of those found in the Danish pig population, we compared the growth of 50 randomly selected strains. The observed net growth rates were used to describe the in vitro pharmacodynamic relationship between drug concentration and net growth rate based on E_max model with three parameters: maximum net growth rate (α_max); concentration for a half-maximal response (E_max); and the Hill coefficient (γ).

Results

The net growth rate in the absence of antibiotic did not differ between susceptible and resistant isolates (P = 0.97). The net growth rate decreased with increasing tetracycline concentrations, and this decline was greater in susceptible strains than resistant strains. The lag phase, defined as the time needed for the strain to reach an OD₆₀₀ value of 0.01, increased exponentially with increasing tetracycline concentration. The pharmacodynamic parameters confirmed that the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \alpha_{max} $$\end{document}αmax between susceptible and resistant strains in the absence of a drug was not different. EC₅₀ increased linearly with MIC on a log–log scale, and γ was different between susceptible and resistant strains.

Conclusions

The in vitro model parameters described the inhibition effect of tetracycline on E. coli when strains were exposed to a wide range of tetracycline concentrations. These parameters, along with in vivo pharmacokinetic data, may be useful in mathematical models to predict in vivo competitive growth of many different strains and for development of optimal dosing regimens for preventing selection of resistance.

Pharmacokinetics/Pharmacodynamics of Peptide Deformylase Inhibitor GSK1322322 against Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus in Rodent Models of Infection

GSK1322322 is a novel inhibitor of peptide deformylase (PDF) with good in vitro activity against bacteria associated with community-acquired pneumonia and skin infections. We have characterized the in vivo pharmacodynamics (PD) of GSK1322322 in immunocompetent animal models of infection with Streptococcus pneumoniae and Haemophilus influenzae (mouse lung model) and with Staphylococcus aureus (rat abscess model) and determined the pharmacokinetic (PK)/PD index that best correlates with efficacy and its magnitude. Oral PK studies with both models showed slightly higher-than-dose-proportional exposure, with 3-fold increases in area under the concentration-time curve (AUC) with doubling doses. GSK1322322 exhibited dose-dependent in vivo efficacy against multiple isolates of S. pneumoniae, H. influenzae, and S. aureus. Dose fractionation studies with two S. pneumoniae and S. aureus isolates showed that therapeutic outcome correlated best with the free AUC/MIC (fAUC/MIC) index in S. pneumoniae (R(2), 0.83), whereas fAUC/MIC and free maximum drug concentration (fCmax)/MIC were the best efficacy predictors for S. aureus (R(2), 0.9 and 0.91, respectively). Median daily fAUC/MIC values required for stasis and for a 1-log10 reduction in bacterial burden were 8.1 and 14.4 for 11 S. pneumoniae isolates (R(2), 0.62) and 7.2 and 13.0 for five H. influenzae isolates (R(2), 0.93). The data showed that for eight S. aureus isolates, fAUC correlated better with efficacy than fAUC/MIC (R(2), 0.91 and 0.76, respectively), as efficacious AUCs were similar for all isolates, independent of their GSK1322322 MIC (range, 0.5 to 4 μg/ml). Median fAUCs of 2.1 and 6.3 μg · h/ml were associated with stasis and 1-log10 reductions, respectively, for S. aureus.