Protein binding of antimicrobials: methods for quantification and for investigation of its impact on bacterial killing

Interspecies variability in protein binding of antibiotics basis for translational PK/PD studies-a case study using cefazolin

For antimicrobial agents in particular, plasma protein binding (PPB) plays a pivotal role in deciphering key properties of drug candidates. Animal models are generally used in the preclinical development of new drugs to predict their effects in humans using translational pharmacokinetics/pharmacodynamics (PK/PD). Thus, we compared the protein binding (PB) of cefazolin as well as bacterial growth under various conditions in vitro. The PB extent of cefazolin was studied in human, bovine, and rat plasmas at different antibiotic concentrations in buffer and media containing 20-70% plasma or pure plasma using ultrafiltration (UF) and equilibrium dialysis (ED). Moreover, bacterial growth and time-kill assays were performed in Mueller Hinton Broth (MHB) containing various plasma percentages. The pattern for cefazolin binding to plasma proteins was found to be similar for both UF and ED. There was a significant decrease in cefazolin binding to bovine plasma compared to human plasma, whereas the pattern in rat plasma was more consistent with that in human plasma. Our growth curve analysis revealed considerable growth inhibition of Escherichia coli at 70% bovine or rat plasma compared with 70% human plasma or pure MHB. As expected, our experiments with cefazolin at low concentrations showed that E. coli grew slightly better in 20% human and rat plasma compared to MHB, most probably due to cefazolin binding to proteins in the plasma. Based on the example of cefazolin, our study highlights the interspecies differences of PB with potential impact on PK/PD. These findings should be considered before preclinical PK/PD data can be extrapolated to human patients.

Effect of albumin substitution on pharmacokinetics of piperacillin/tazobactam in patients with severe burn injury admitted to the ICU

BACKGROUND

Pathophysiological changes in severely burned patients alter the pharmacokinetics (PK) of anti-infective agents, potentially leading to subtherapeutic concentrations at the target site. Albumin supplementation, to support fluid resuscitation, may affect pharmacokinetic properties by binding drugs. This study aimed to investigate the PK of piperacillin/tazobactam in burn patients admitted to the ICU before and after albumin substitution as total and unbound concentrations in plasma.

PATIENTS AND METHODS

Patients admitted to the ICU and scheduled for 4.5 g piperacillin/tazobactam administration and 200 mL of 20% albumin substitution as part of clinical routine were included. Patients underwent IV microdialysis, and simultaneous arterial plasma sampling, at baseline and multiple timepoints after drug administration. PK analysis of total and unbound drug concentrations under steady-state conditions was performed before and after albumin supplementation.

RESULTS

A total of seven patients with second- to third-degree burns involving 20%-60% of the total body surface were enrolled. Mean (SD) AUC0-8 (h·mg/L) of total piperacillin/tazobactam before and after albumin substitution were 402.1 (242)/53.2 (27) and 521.8 (363)/59.7 (32), respectively. Unbound mean AUC0-8 before and after albumin supplementation were 398.9 (204)/54.5 (25) and 456.4 (439)/64.5 (82), respectively.

CONCLUSIONS

Albumin supplementation had little impact on the PK of piperacillin/tazobactam. After albumin supplementation, there was a numerical increase in mean AUC0-8 of total and unbound piperacillin/tazobactam, whereas similar Cmax values were observed. Future studies may investigate the effect of albumin supplementation on drugs with a higher plasma protein binding.

Microstructure, Physical and Biological Properties, and BSA Binding Investigation of Electrospun Nanofibers Made of Poly(AA-co-ACMO) Copolymer and Polyurethane

In this study, poly(AA-co-ACMO) and polyurethane-based nanofibers were prepared in a ratio of 1:1 (NF11) and 2:1 (NF21) as antimicrobial carriers for chronic wound management. Different techniques were used to characterize the nanofibers, and poly(AA-co-ACMO) was mostly found on the surface of PU. With an increase in poly(AA-co-ACMO) dose from 0 (PU) and 1:1 (NF11) to 2:1 (NF21) in the casting solution, the contact angle (CA) was reduced from 137 and 95 to 24, respectively, and hydrophilicity was significantly increased. As most medications inhibit biological processes by binding to a specific protein, in vitro protein binding was investigated mechanistically using a stopped-flow technique. Both NF11 and NF21 bind to BSA via two reversible steps: a fast second-order binding followed by a slow first-order one. The overall parameters for NF11 (K_a = 1.1 × 10⁴ M^-1, K_d = 89.0 × 10^-6, ΔG⁰ = -23.1 kJ mol^-1) and NF21 (K_a = 189.0 × 10⁴ M^-1, K_d = 5.3 × 10^-6 M, ΔG⁰ = -27.5 kJ mol^-1) were determined and showed that the affinity for BSA is approximately (NF11)/(NF21) = 1/180. This indicates that NF21 has much higher BSA affinity than NF11, although BSA interacts with NF11 much faster. NF21 with higher hydrophilicity showed effective antibacterial properties compared to NF11, in agreement with kinetic data. The study provided an approach to manage chronic wounds and treating protein-containing wastewater.

A rapid, simple, high-performance liquid chromatography method for the clinical measurement of beta-lactam antibiotics in serum and interstitial fluid

Background: enhanced methods of therapeutic drug monitoring are required to support the individualisation of antibiotic dosing based on pharmacokinetics (PK) parameters. PK studies can be hampered by limited total serum volume, especially in neonates, or by sensitivity in the case of critically ill patients. We aimed to develop a liquid chromatography-mass spectrometry (LC/MS) analysis of benzylpenicillin, phenoxymethylpenicillin and amoxicillin in single low volumes of human serum and interstitial fluid (ISF) samples, with an improved limit of detection (LOD) and limit of quantification (LOQ), compared with previously published assays. Methods: sample clean-up was performed by protein precipitation using acetonitrile. Reverse phase chromatography was performed using triple quadrupole LC/MS. The mobile phase consisted of 55% methanol in water + 0.1% formic acid, with a flow rate of 0.4 mL min^-1. Antibiotics stability was assessed at different temperatures. Results: chromatographic separation was achieved within 3 minutes for all analytes. Three common penicillins can now be measured in a single low-volume blood and ISF sample (15 μL) for the first time. Validation has demonstrated the method to be linear over the range 0.0015-10 mg L^-1, with an accuracy of 93-104% and high sensitivity, with LOD ≈ 0.003 mg L^-1 and LOQ ≈ 0.01 mg L^-1 for all three analytes, which is critical for use in dose optimisation/individualisation. All evaluated penicillins indicated good stability at room temperature over 4 h, at (4 °C) over 24 h and at -80 °C for 6 months. Conclusion: the developed method is simple, rapid, accurate and clinically applicable for the quantification of three penicillin classes.

Triple quadrupole LC/MS method for the simultaneous quantitative measurement of cefiderocol and meropenem in serum

Background: therapeutic drug monitoring is a crucial aspect of the management of hospitalized patients. The correct dosage of antibiotics is imperative to ensure their adequate exposure specially in critically ill patients. The aim of this study is to establish and validate a robust and fast liquid chromatography-tandem mass spectrometry (LC/MS) method for the simultaneous quantification of two important antibiotics in critically ill patients, cefiderocol and meropenem in human plasma. Methods: sample clean-up was performed by protein precipitation using acetonitrile. Reverse phase chromatography was performed using triple quadrupole LC/MS. The mobile phase was consisted of 55% methanol in water +0.1% formic acid, with flow rate of 0.4 ml min^-1. Antibiotics stability was assessed at different temperatures. Serum protein binding was assessed using ultrafiltration devices. Results: chromatographic separation was achieved within 1.5 minutes for all analytes. Validation has demonstrated the method to be linear over the range 0.0025-50 mg L^-1 for cefiderocol and 0.00028-50 mg L^-1 for meropenem, with accuracy of 94-101% and highly sensitive, with LLOQ ≈ 0.02 mg L^-1 and 0.003 mg L^-1 for cefiderocol and meropenem, respectively. Both cefiderocol and meropenem showed a good stability at room temperature over 6 h, and at (4 °C) over 24 h. Cefiderocol and meropenem demonstrated a protein binding of 49-60% and 98%, respectively in human plasma. Conclusion: the developed method is simple, rapid, accurate and clinically applicable for the quantification of cefiderocol and meropenem.

Comparison of ultrafiltration and microdialysis for ceftriaxone protein-binding determination

BACKGROUND

High protein binding (PB) of antibiotics has an impact on their antimicrobial activity. It has been questioned whether in vitro PB determination can capture the dynamic and concentration-dependent PB of highly bound antibiotics.

OBJECTIVES

This clinical study compared in vitro ultrafiltration (UF) and in vivo IV microdialysis (MD) methods to determine ceftriaxone PB.

METHODS

Six healthy male volunteers received a single IV 2 g dose of ceftriaxone. Unbound ceftriaxone plasma concentrations were measured with MD and venous plasma sampling with subsequent UF. Pharmacokinetic parameters were determined using non-compartmental pharmacokinetic analysis. Non-linear mixed-effects modelling was used to quantify the PB. The PTA was estimated.

RESULTS

The Cmax of ceftriaxone total plasma concentration (297.42 ± 21.0 mg/L) was approximately 5.5-fold higher than for free concentrations obtained with UF (52.83 ± 5.07 mg/L), and only 3.5-fold higher than for free concentrations obtained with MD (81.37 ± 26.93 mg/L). Non-linear, saturable PB binding was confirmed for both UF and MD. Significantly different dissociation constants (Kd) for the albumin/ceftriaxone complex were quantified: in UF it was 23.7 mg/L (95% CI 21.3-26.2) versus 15.9 mg/L (95% CI 13.6-18.6) in MD. Moreover, the estimated number of binding sites (95% CI) per albumin molecule was 0.916 (0.86-0.97) in UF versus 0.548 in MD (0.51-0.59). The PTA obtained with MD was at most 27% higher than with UF.

CONCLUSIONS

In vitro UF versus in vivo intravasal MD revealed significantly different PB, especially during the distribution phase. The method of PB determination could have an impact on the breakpoint determination and dose optimisation of antibiotics.

Study protocol of REpeat versus SIngle ShoT Antibiotic prophylaxis in major Abdominal Surgery (RESISTAAS I): a prospective observational study of antibiotic prophylaxis practice for patients undergoing major abdominal surgery

INTRODUCTION

Surgical site infections (SSIs) are among the most common complications after abdominal surgery and develop in approximately 20% of patients. These patients suffer a 12% increase in mortality, underlying the need for strategies reducing SSI. Perioperative antibiotic prophylaxis is paramount for SSI prevention in major abdominal surgery. Yet, intraoperative redosing criteria are subjective and whether patients benefit from it remains unclear.

METHODS AND ANALYSIS

The REpeat versus SIngle ShoT Antibiotic prophylaxis in major Abdominal Surgery (RESISTAAS I) study is a single-centre, prospective, observational study investigating redosing of antibiotic prophylaxis in 300 patients undergoing major abdominal surgery. Adult patients scheduled for major abdominal surgery will be included. Current practice of redosing regarding number and time period will be recorded. Postoperative SSIs, nosocomial infections, clinically relevant infection-associated bacteria, postoperative antibiotic treatment, in addition to other clinical, pharmacological and economical outcomes will be evaluated. Differences between groups will be analysed with analysis of covariance.

ETHICS AND DISSEMINATION

RESISTAAS I will be conducted in accordance with the Declaration of Helsinki and internal, national and international standards of GCP. The Medical Ethics Review Board of Heidelberg University has approved the study prior to initiation (S-404/2021). The study has been registered on 7 February 2022 at German Clinical Trials Register, with identifier DRKS00027892. We plan to disseminate the results of the study in a peer-reviewed journal.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS): DRKS00027892.

Protein Binding in Translational Antimicrobial Development-Focus on Interspecies Differences

Background/Introduction: Plasma protein binding (PPB) continues to be a key aspect of antibiotic development and clinical use. PPB is essential to understand several properties of drug candidates, including antimicrobial activity, drug-drug interaction, drug clearance, volume of distribution, and therapeutic index. Focus areas of the review: In this review, we discuss the basics of PPB, including the main drug binding proteins i.e., Albumin and α-1-acid glycoprotein (AAG). Furthermore, we present the effects of PPB on the antimicrobial activity of antibiotics and the current role of PPB in in vitro pharmacodynamic (PD) models of antibiotics. Moreover, the effect of PPB on the PK/PD of antibiotics has been discussed in this review. A key aspect of this paper is a concise evaluation of PPB between animal species (dog, rat, mouse, rabbit and monkey) and humans. Our statistical analysis of the data available in the literature suggests a significant difference between antibiotic binding in humans and that of dogs or mice, with the majority of measurements from the pre-clinical species falling within five-fold of the human plasma value. Conversely, no significant difference in binding was found between humans and rats, rabbits, or monkeys. This information may be helpful for drug researchers to select the most relevant animal species in which the metabolism of a compound can be studied for extrapolating the results to humans. Furthermore, state-of-the-art methods for determining PPB such as equilibrium dialysis, ultracentrifugation, microdialysis, gel filtration, chromatographic methods and fluorescence spectroscopy are highlighted with their advantages and disadvantages.

An Overview of the Protein Binding of Cephalosporins in Human Body Fluids: A Systematic Review

Introduction: Protein binding can diminish the pharmacological effect of beta-lactam antibiotics. Only the free fraction has an antibacterial effect. The aim of this systematic literature review was to give an overview of the current knowledge of protein binding of cephalosporins in human body fluids as well as to describe patient characteristics influencing the level of protein binding.

Method: A systematic literature search was performed in Embase, Medline ALL, Web of Science Core Collection and the Cochrane Central Register of Controlled Trials with the following search terms: “protein binding,” “beta-lactam antibiotic,” and “body fluid.” Only studies were included where protein binding was measured in humans in vivo.

Results: The majority of studies reporting protein binding were performed in serum or plasma. Other fluids included pericardial fluid, blister fluid, bronchial secretion, pleural exudate, wound exudate, cerebrospinal fluid, dialysate, and peritoneal fluid. Protein binding differs between diverse cephalosporins and between different patient categories. For cefazolin, ceftriaxone, cefpiramide, and cefonicid a non-linear pattern in protein binding in serum or plasma was described. Several patient characteristics were associated with low serum albumin concentrations and were found to have lower protein binding compared to healthy volunteers. This was for critically ill patients, dialysis patients, and patients undergoing cardiopulmonary bypass during surgery. While mean/median percentages of protein binding are lower in these patient groups, individual values may vary considerably. Age is not likely to influence protein binding by itself, however limited data suggest that lower protein binding in newborns. Obesity was not correlated with altered protein binding.

Discussion/Conclusion: Conclusions on protein binding in other body fluids than blood cannot be drawn due to the scarcity of data. In serum and plasma, there is a large variability in protein binding per cephalosporin and between different categories of patients. Several characteristics were identified which lead to a lower protein binding. The finding that some of the cephalosporins display a non-linear pattern of protein binding makes it even more difficult to predict the unbound concentrations in individual patients. Taken all these factors, it is recommended to measure unbound concentrations to optimize antibiotic exposure in individual patients.

Systematic Review Registration: PROSPERO, identifier (CRD42021252776).

Pharmacokinetics and Pharmacodynamics of Fungal Defensin NZX Against Staphylococcus aureus-Induced Mouse Peritonitis Model

Staphylococcus aureus (S. aureus) is one of the most common pathogenic bacteria responsible for causing a life-threatening peritonitis disease. NZX, as a variant of fungal defensin plectasin, displayed potent antibacterial activity against S. aureus. In this study, the antibacterial and resistance characteristics, pharmacokinetics, and pharmacodynamics of NZX against the S. aureus E48 and S. aureus E48-induced mouse peritonitis model were studied, respectively. NZX exhibited a more rapid killing activity to S. aureus (minimal inhibitory concentration, 1 μg/ml) compared with linezolid, ampicillin and daptomycin, and serial passaging of S. aureus E48 for 30 days at 1/2 × MIC, NZX had a lower risk of resistance compared with ampicillin and daptomycin. Also, it displayed a high biocompatibility and tolerance to physiological salt, serum environment, and phagolysosome proteinase environment, except for acid environment in phagolysosome. The murine serum protein-binding rate of NZX was 89.25% measured by ultrafiltration method. Based on the free NZX concentration in serum after tail vein administration, the main pharmacokinetic parameters for T_1/2, C_max, V_d, MRT, and AUC ranged from 0.32 to 0.45 h, 2.85 to 20.55 μg/ml, 1469.10 to 2073.90 ml/kg, 0.32 to 0.56 h, and 1.11 to 8.89 μg.h/ml, respectively. Additionally, the in vivo pharmacodynamics against S. aureus demonstrated that NZX administrated two times by tail vein at 20 mg/kg could rescue all infected mice in the lethal mouse peritonitis model. And NZX treatment (20 mg/kg) significantly reduced CFU counts in the liver, lung, and spleen, especially for intracellular bacteria in the peritoneal fluid, which were similar or superior to those of daptomycin. In vivo efficacies of NZX against total bacteria and intracellular bacteria were significantly correlated with three PK/PD indices of ƒAUC/MIC, ƒC_max/MIC, and ƒT% > MIC analyzed by a sigmoid maximum-effect model. These results showed that NZX may be a potential candidate for treating peritonitis disease caused by intracellular S. aureus.

Armeniaspirol analogues with more potent Gram-positive antibiotic activity show enhanced inhibition of the ATP-dependent proteases ClpXP and ClpYQ

Antibiotics with fundamentally new mechanisms of action such as the armeniaspirols, which target the ATP-dependent proteases ClpXP and ClpYQ, must be developed to combat antimicrobial resistance. While the mechanism of action of armeniaspirol against Gram-positive bacteria is understood, little is known about the structure-activity relationship for its antibiotic activity. Based on the preliminary data showing that modifications of armeniaspirol's N-methyl group increased antibiotic potency, we probed the structure-activity relationship of N-alkyl armeniaspirol derivatives. A series of focused derivatives were synthesized and evaluated for antibiotic activity against clinically relevant pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. Replacement of the N-methyl with N-hexyl, various N-benzyl, and N-phenethyl substituents led to substantial increases in antibiotic activity and potency for inhibition of both ClpYQ and ClpXP. Docking studies identified binding models for ClpXP and ClpYQ that were consistent with the inhibition data. This work confirms the role of ClpXP and ClpYQ in the mechanism of action of armeniaspirol and provides important lead compounds for further antibiotic development.

Albumin in Tears Modulates Bacterial Susceptibility to Topical Antibiotics in Ophthalmology

Bacterial keratitis is a serious and vision-threatening condition in veterinary and human patients, one that often requires culture and susceptibility testing to adjust therapy and improve clinical outcomes. The present study challenges the antimicrobial susceptibility testing (AST) paradigm in ophthalmology, enabling more accurate in vitro-to-in vivo translation by incorporating factors normally present during host-pathogen interactions in clinical patients. Thirty bacteria (10 Staphylococcus pseudintermedius, 10 Streptococcus canis, 10 Pseudomonas aeruginosa) were isolated from canine patients with infectious keratitis. For each isolate, commercial plates (Sensititre™ JOEYE2) were used to assess the minimal inhibitory concentration (MIC) of 17 different antibiotics in the absence (0% albumin, control) or presence of canine albumin (0.01–2%). For Staphylococcus pseudintermedius, the experiment was repeated with actual tear fluid collected from canine eyes with ocular surface inflammation. Kruskal-Wallis, Wilcoxon signed rank test and Spearman's correlation tests were used for statistical analysis. Clinical outcomes were unfavorable in selected canine patients with bacterial keratitis (e.g., globe perforation, graft dehiscence) despite standard AST (i.e., 0% albumin in test medium) confirming that most corneal infections (93%) were susceptible to ≥1 topical antibiotics used at the initial visit. Albumin levels ≥0.05% increased MICs in a dose-dependent, bacteria-specific, and antibiotic-specific manner. No significant differences (P = 1.000) were noted in MICs of any antibiotic whether albumin or tear fluid was added to the Mueller-Hinton broth. Percent protein binding inherent to each antibiotic was associated with clinical interpretations (Spearman's rho = −0.53, P = 0.034) but not changes in MICs. Albumin in tears impacted the efficacy of selected ophthalmic antibiotics as only the unbound portion of an antibiotic is microbiologically active. The present findings could improve decision making of clinicians managing bacterial keratitis, reduce development of antimicrobial resistance, influence current guidelines set by the Clinical and Laboratory Standards Institute, and serve as a reference for bacteriological evaluations across medical fields and across species.

Population Pharmacokinetics of Intravenous Amoxicillin Combined With Clavulanic Acid in Healthy and Critically Ill Dogs

Background: Data regarding antimicrobial pharmacokinetics (PK) in critically ill dogs are lacking and likely differ from those of healthy dogs. The aim of this work is to describe a population PK model for intravenous (IV) amoxicillin–clavulanic acid (AMC) in both healthy and sick dogs and to simulate a range of clinical dosing scenarios to compute PK/PD cutoffs for both populations.

Methods: This study used a prospective clinical trial in normal and critically ill dogs. Twelve client-owned dogs hospitalized in the intensive care unit (ICU) received IV AMC 20 mg/kg every 8 h (0.5-h infusion) during at least 48 h. Eight blood samples were collected at predetermined times, including four trough samples before the next administration. Clinical covariates and outcome were recorded, including survival to discharge and bacteriologic clinical failure. Satellite PK data were obtained de novo from a group of 12 healthy research dogs that were dosed with a single AMC 20 mg/kg IV. Non-linear mixed-effects model was used to estimate the PK parameters (and the effect of health upon them) together with variability within and between subjects. Monte Carlo simulations were performed with seven dosage regimens (standard and increased doses). The correlation between model-derived drug exposure and clinical covariates was tested with Spearman's non-parametric correlation analysis. Outcome was recorded including survival to discharge and bacteriologic clinical failure.

Results: A total of 218 amoxicillin concentrations in plasma were available for healthy and sick dogs. A tricompartmental model best described the data. Amoxicillin clearance was reduced by 56% in sick dogs (0.147 L/kg/h) compared with healthy dogs (0.336 L/kg/h); intercompartmental clearance was also decreased (p <0.01). None of the clinical data covariates were significantly correlated with individual exposure. Monte Carlo simulations showed that higher PK/PD cutoff values of 8 mg/L could be reached in sick dogs by extending the infusion to 3 h or doubling the dose.

Conclusions: The PK of AMC is profoundly different in critically ill dogs compared with normal dogs, with much higher interindividual variability and a lower systemic clearance. Our study allows to generate hypotheses with regard to higher AMC exposure in clinical dogs and provides supporting data to revise current AMC clinical breakpoint for IV administration.

Composition and biological assays of the leaf essential oil of Asparagus flagellaris (Kunth) Bak

Background

Asparagus flagellaris leaves are ethnomedicinally used to treat syphilis, gonorrhea and other sexually transmitted diseases (STDs), with no reports on the volatile constituents. This study was aimed to quantitatively and qualitatively characterise the composition of essential oil, evaluates the free radical scavenging and antimicrobial capacity of the essential oil.

Methods

The essential oil was isolated by hydrodistillation method using all-glass Clevenger-type apparatus, while the identification and quantification of constituents were performed by gas chromatography-mass spectrometry (GC-MS) technique. The antioxidant activity on 2, 2-diphenyl-1-picrylhydrazyl (DPPH) was evaluated and the oil was also tested against 10 strains of microorganisms consisting of 6 bacteria: Escherichia coli, Salmonella typhi, Klebsiella pneumonia, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis and 4 fungi: Candida albicans, Penicillium notatum, Aspergillus niger and Rhizopus spp. using broth dilution and surface plate methods, respectively.

Results

A pale yellow essential oil with a characteristic scent was obtained, with a yield of 0.80% (w/w). A total of 28 compounds accounting for 97.41% of the total oil contents were identified. The oil was predominated by Thymol and its derivatives, accounting for 57.48%. The most abundance (% area) constituents of the essential oil were 5-Thymyl tiglate (18.49%), Thymyl-2-methyl butyrate (17.34%), Thymol hydroquinone dimethyl ether (10.52%), Thymol methyl ether (9.42%) and 5-Propyl-1, 3-benzodioxole (4.59%). The essential oil showed a significant free radical scavenging activity compared to the standard antioxidant drugs used in this study, with % inhibition varying from 88.06 ± 0.0001 to 93.05 ± 0.0006. The leaf essential oil exhibited antimicrobial activity on all the tested organisms at 500–125 μg/mL, with an 18–10 mm inhibitory zone.

Conclusion

The leaf essential oil of A. flagellaris contains notable chemical compounds responsible for its antioxidant and antimicrobial activities.

Antibacterial Profile of a Microbicidal Agent Targeting Tyrosine Phosphatases and Redox Thiols, Novel Drug Targets

The activity profile of a protein tyrosine phosphatase (PTP) inhibitor and redox thiol oxidant, nitropropenyl benzodioxole (NPBD), was investigated across a broad range of bacterial species. In vitro assays assessed inhibitory and lethal activity patterns, the induction of drug variants on long term exposure, the inhibitory interactions of NPBD with antibiotics, and the effect of plasma proteins and redox thiols on activity. A literature review indicates the complexity of PTP and redox signaling and suggests likely metabolic targets. NPBD was broadly bactericidal to pathogens of the skin, respiratory, urogenital and intestinal tracts. It was effective against antibiotic resistant strains and slowly replicating and dormant cells. NPBD did not induce resistant or drug-tolerant phenotypes and showed low cross reactivity with antibiotics in synergy assays. Binding to plasma proteins indicated lowered in-vitro bioavailability and reduction of bactericidal activity in the presence of thiols confirmed the contribution of thiol oxidation and oxidative stress to lethality. This report presents a broad evaluation of the antibacterial effect of PTP inhibition and redox thiol oxidation, illustrates the functional diversity of bacterial PTPs and redox thiols, and supports their consideration as novel targets for antimicrobial drug development. NPBD is a dual mechanism agent with an activity profile which supports consideration of tyrosine phosphatases and bacterial antioxidant systems as promising targets for drug development.

Protein binding of clindamycin in vivo by means of intravascular microdialysis in healthy volunteers

OBJECTIVES

The efficacy of an anti-infective drug is influenced by its protein binding (PB), since only the free fraction is active. We hypothesized that PB may vary in vitro and in vivo, and used clindamycin, a drug with high and concentration-dependent PB to investigate this hypothesis.

METHODS

Six healthy volunteers received a single intravenous infusion of clindamycin 900 mg. Antibiotic plasma concentrations were obtained by blood sampling and unbound drug concentrations were determined by means of in vivo intravascular microdialysis (MD) or in vitro ultrafiltration (UF) for up to 8 h post dosing. Clindamycin was assayed in plasma and MD fluid using a validated HPLC-UV (ultraviolet) method. Non-linear mixed effects modelling in NONMEM® was used to quantify the PB in vivo and in vitro.

RESULTS

C max was 14.95, 3.39 and 2.32 mg/L and AUC0-8h was 41.78, 5.80 and 6.14 mg·h/L for plasma, ultrafiltrate and microdialysate, respectively. Calculated ratio of AUCunbound/AUCtotal showed values of 13.9%±1.8% and 14.7%±3.1% for UF and microdialysate, respectively. Modelling confirmed non-linear, saturable PB for clindamycin with slightly different median (95% CI) dissociation constants (Kd) for the alpha-1 acid glycoprotein (AAG)-clindamycin complex of 1.16 mg/L (0.91-1.37) in vitro versus 0.85 mg/L (0.58-1.01) in vivo. Moreover, the estimated number of binding sites per AAG molecule was 2.07 (1.79-2.25) in vitro versus 1.66 in vivo (1.41-1.79).

CONCLUSIONS

Concentration-dependent PB was observed for both investigated methods with slightly lower levels of unbound drug fractions in vitro as compared with in vivo.

Prediction of Minocycline Activity in the Gut From a Pig Preclinical Model Using a Pharmacokinetic -Pharmacodynamic Approach

The increase of multidrug-resistant (MDR) bacteria has renewed interest in old antibiotics, such as minocycline, that can be active against various MDR Gram-negative pathogens. The elimination of minocycline by both kidneys and liver makes it suitable for impaired renal function patients. However, the drawback is the possible elimination of a high amount of drug in the intestines, with potential impact on the digestive microbiota during treatment. This study aimed to predict the potential activity of minocycline against Enterobacterales in the gut after parenteral administration, by combining in vivo and in vitro studies. Total minocycline concentrations were determined by UPLC-UV in the plasma and intestinal content of piglets following intravenous administration. In parallel, the in vitro activity of minocycline was assessed against two Escherichia coli strains in sterilized intestinal contents, and compared to activity in a standard broth. We found that minocycline concentrations were 6–39 times higher in intestinal contents than plasma. Furthermore, minocycline was 5- to 245-fold less active in large intestine content than in a standard broth. Using this PK-PD approach, we propose a preclinical pig model describing the link between systemic and gut exposure to minocycline, and exploring its activity against intestinal Enterobacterales by taking into account the impact of intestinal contents.

Microsampling Assays for Pharmacokinetic Analysis and Therapeutic Drug Monitoring of Antimicrobial Drugs in Children: A Critical Review

BACKGROUND

With the increasing prevalence of multidrug resistant organisms, therapeutic drug monitoring (TDM) has become a common tool for assuring the safety and efficacy of antimicrobial drugs at higher doses. Microsampling techniques, including dried blood spotting (DBS) and volumetric absorptive microsampling (VAMS), are attractive tools for TDM and pediatric clinical research. For microsampling techniques to be a useful tool for TDM, it is necessary to establish the blood-plasma correlation and the therapeutic window of antimicrobial drugs in the blood.

METHODS

DBS involves the collection of small volumes of blood (30-50 µL per spot) on a filter paper, whereas VAMS allows the accurate and precise collection of a fixed volume of blood (10-30 µL) with microsampling devices. One of the major advantages of VAMS is that it reduces or eliminates the volumetric blood hematocrit (HCT) bias associated with DBS. Liquid chromatography with tandem mass spectrometry is a powerful tool for the accurate quantification of antimicrobial drugs from small volumes of blood specimens.

RESULTS

This review summarizes the recent liquid chromatography with tandem mass spectrometry assays that have used DBS and VAMS approaches for quantifying antimicrobial drugs. Sample collection, extraction, validation outcomes, including the interassay and intra-assay accuracy and precision, recovery, stability, and matrix effect, as well as the clinical application of these assays and their potential as tools of TDM are discussed herein.

CONCLUSIONS

Microsampling techniques, such as VAMS, provide an alternative approach to traditional plasma sample collection for TDM.

Current In Vitro Biofilm-Infected Chronic Wound Models for Developing New Treatment Possibilities

Significance: The prevalence of chronic wounds is increasing worldwide. The most recent estimates suggest that up to 2% of the population in the industrialized countries is affected. Recent Advances: During the past few decades, bacterial biofilms have been elucidated as one of the primary reasons why chronic wounds fail to heal. Critical Issues: There is a lack of direct causation and evidence of the role that biofilms play in persistent wounds, which complicates research on new treatment options, since it is still unknown which factors dominate. For this reason, several different in vitro wound models that mimic the biofilm infections observed in chronic wounds and other chronic infections have been created. These different models are, among other purposes, used to test a variety of wound care products. However, chronic wounds are highly complex, and several different factors must be taken into consideration along with the infection, including physiochemical and human-supplemented factors. Furthermore, the limitations of using in vitro models, such as the lack of a responsive immune system should always be given due consideration. Future Directions: Present understandings of all the elements and interactions that take place within chronic wounds are incomplete. As our insight of in vivo chronic wounds continues to expand, so too must the in vitro models used to mimic these infections evolve and adapt to new knowledge.

Assay validation and determination of in vitro binding of mefloquine to plasma proteins from clinically normal and FIP-affected cats

The antimalarial agent mefloquine is currently being investigated for its potential to inhibit feline coronavirus and feline calicivirus infections. A simple, high pressure liquid chromatography assay was developed to detect mefloquine plasma concentrations in feline plasma. The assay’s lower limit of quantification was 250 ng/mL. The mean ± standard deviation intra- and inter-day precision expressed as coefficients of variation were 6.83 ± 1.75 and 5.33 ± 1.37%, respectively, whereas intra- and inter-day accuracy expressed as a percentage of the bias were 11.40 ± 3.73 and 10.59 ± 3.88%, respectively. Accordingly, this validated assay should prove valuable for future in vivo clinical trials of mefloquine as an antiviral agent against feline coronavirus and feline calicivirus. However, the proportion of mefloquine binding to feline plasma proteins has not been reported. The proportion of drug bound to plasma protein binding is an important concept when developing drug dosing regimens. As cats with feline infectious peritonitis (FIP) demonstrate altered concentrations of plasma proteins, the proportion of mefloquine binding to plasma proteins in both clinically normal cats and FIP-affected cats was also investigated. An in vitro method using rapid equilibrium dialysis demonstrated that mefloquine was highly plasma protein bound in both populations (on average > 99%).

Comparative Plasma Pharmacokinetics of Ceftriaxone and Ertapenem in Normoalbuminemia, Hypoalbuminemia, and Albumin Replacement in a Sheep Model

Optimal concentrations of unbound antimicrobials are essential for a maximum microbiological effect. Although hypoalbuminemia and albumin fluid resuscitation are common in critical care, the effects of different albumin concentrations on the unbound concentrations of highly protein-bound antimicrobials are not known. The aim of this study was to compare the effects of different albumin states on total and unbound concentrations of ertapenem and ceftriaxone using an ovine model. The study design was a prospective, three-phase intervention observational study. The subjects were healthy Merino sheep. Eight sheep were subjected to three experimental phases: normoalbuminemia, hypoalbuminemia using plasmapheresis, and albumin replacement using a 25% albumin solution. In each phase, ceftriaxone at 40 mg/kg of body weight and ertapenem at 15 mg/kg were given intravenously. Blood samples were collected at predefined intervals and analyzed using an ultrahigh-performance liquid chromatography-tandem mass spectrometry method. Pharmacokinetic parameters such as the area under the curve from 0 to 24 h (AUC_0-24), plasma clearance (CL), and apparent volume of distribution in the terminal phase (V) were estimated and compared between the phases. The protein and albumin concentrations were significantly different between phases. Hypoalbuminemia resulted in a significantly lower AUC_0-24 and higher CL of total and unbound concentrations of ceftriaxone than in the other phases, whereas albumin replacement led to higher AUC_0-24 and lower CL than in the other phases for both drugs. The V values for total drug concentrations for both drugs were significantly lower with albumin replacement. For highly protein-bound drugs such as ceftriaxone and ertapenem, both hypoalbuminemia and albumin replacement may affect unbound drug exposure.

Paclitaxel, Imatinib and 5-Fluorouracil Increase the Unbound Fraction of Flucloxacillin In Vitro

Flucloxacillin (FLU), an isoxazolyl penicillin, is widely used for the treatment of different bacterial infections in intensive care units (ICU). Being highly bound to plasma proteins, FLU is prone to drug-drug interactions (DDI) when administered concurrently with other drugs. As FLU is binding to both Sudlow’s site I and site II of human serum albumin (HSA), competitive and allosteric interactions with other drugs, highly bound to the same sites, seem conceivable. Knowledge about interaction(s) of FLU with the widely used anticancer agents paclitaxel (PAC), imatinib (IMA), and 5-fluorouracil (5-FU is scarce. The effects of the selected anticancer agents on the unbound fraction of FLU were evaluated in pooled plasma as well as in HSA and α-1-acid glycoprotein (AGP) samples, the second major drug carrier in plasma. FLU levels in spiked samples were analyzed by LC-MS/MS after ultrafiltration. Significant increase in FLU unbound fraction was observed when in combination with PAC and IMA and to a lesser extent with 5-FU. Furthermore, significant binding of FLU to AGP was observed. Collectively, this is the first study showing the binding of FLU to AGP as well as demonstrating a significant DDI between PAC/IMA/5-FU and FLU.

Measuring Unbound Versus Total Piperacillin Concentrations in Plasma of Critically Ill Patients: Methodological Issues and Relevance

BACKGROUND

Piperacillin is considered a moderately protein-bound antibiotic (20%-40%), with albumin being an important binding protein. Although infrequently used in practice, different methods to measure the fraction unbound (fu) are available, but uncertainty remains as to what the most appropriate method is. The main goal of this study was to estimate the impact of the methodology used to measure unbound piperacillin in plasma on the fu of piperacillin; we compared ultrafiltration (UF) at 4°C and 37°C with the reference method, equilibrium dialysis. In addition, we analyzed the impact of other proteins on the fu.

METHODS

Anonymized left-over Li-heparin plasma samples (n = 41) from 30 critically ill patients who were treated with piperacillin were used for the analyses.

RESULTS

We found that the piperacillin fu, determined by UF, is on average 8% higher at 37°C (91%) than at 4°C (83%). There were no systematic or proportional differences between UF at 4°C and equilibrium dialysis at 4°C. This emphasizes the importance of the temperature during UF, which should therefore be clearly stated in publications that report on the methodology of UF. No significant impact of the albumin-, IgA-, total protein-, or α1-acid glycoprotein concentration on the fu was found. The fu found in this study was higher than the generally assumed fu value of 60%-80%. A possible explanation lies in the studied population or in the temperature used. Based on our results, routine monitoring of unbound piperacillin in intensive care unit patients is not recommended.

CONCLUSIONS

Based on the prediction model, we can state that in intensive care patients the fu of piperacillin is 91% (SD 7%), determined with UF at 37°C.

Profiling antimicrobial peptides from the medical maggot Lucilia sericata as potential antibiotics for MDR Gram-negative bacteria

Background

The ability of MDR Gram-negative bacteria to evade even antibiotics of last resort is a severe global challenge. The development pipeline for conventional antibiotics cannot address this issue, but antimicrobial peptides (AMPs) offer an alternative solution.

Objectives

Two insect-derived AMPs (LS-sarcotoxin and LS-stomoxyn) were profiled to assess their suitability for systemic application in humans.

Methods

The peptides were tested against an extended panel of 114 clinical MDR Gram-negative bacterial isolates followed by time–kill analysis, interaction studies and assays to determine the likelihood of emerging resistance. In further in vitro studies we addressed cytotoxicity, cardiotoxicity and off-target interactions. In addition, an in vivo tolerability and pharmacokinetic study in mice was performed.

Results

LS-sarcotoxin and LS-stomoxyn showed potent and selective activity against Gram-negative bacteria and no cross-resistance with carbapenems, fluoroquinolones or aminoglycosides. Peptide concentrations of 4 or 8 mg/L inhibited 90% of the clinical MDR isolates of Escherichia coli, Enterobacter cloacae, Acinetobacter baumannii and Salmonella enterica isolates tested. The ‘all-d’ homologues of the peptides displayed markedly reduced activity, indicating a chiral target. Pharmacological profiling revealed a good in vitro therapeutic index, no cytotoxicity or cardiotoxicity, an inconspicuous broad-panel off-target profile, and no acute toxicity in mice at 10 mg/kg. In mouse pharmacokinetic experiments LS-sarcotoxin and LS-stomoxyn plasma levels above the lower limit of quantification (1 and 0.25 mg/mL, respectively) were detected after 5 and 15 min, respectively.

Conclusions

LS-sarcotoxin and LS-stomoxyn are suitable as lead candidates for the development of novel antibiotics; however, their pharmacokinetic properties need to be improved for systemic administration.

Impact of thrombocytes, on bacterial growth and antimicrobial activity of selected antibiotics

In vitro pharmacodynamic models are used to optimize in vivo dosing regimens in antimicrobial drug development. One limiting factor of such models is the lack of host factors such as corpuscular blood components as erythrocytes which have already been shown to impact activity of antibiotics and/or growth of the pathogen. However, the impact of thrombocytes has not previously been investigated. We set out to investigate if the addition of thrombocytes (set to physiological concentrations in blood of healthy human, i.e., 5 × 10⁵ thrombocytes/μL standard growth media Mueller Hinton Broth, MHB) has an influence on bacterial growth and on the efficacy of antibiotics against Gram+ and Gram− bacteria. Growth assays and time-killing-curves (TKC) were performed with ATCC-strains of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa in triplicate over 24 h. The same approach was followed for 5 clinical isolates of Escherichia coli. Meropenem, ciprofloxacin, and tigecycline were tested as representatives of broad-spectrum antibiotics, and concentrations several-fold above and below the minimal inhibitory concentration (MIC) were simulated. No significant impact of thrombocytes was found on bacterial growth or antimicrobial stability for the investigated agents. Bacteria reduced thrombocyte content to different degree, indicating direct interaction of pathogens and thrombocytes. Impact on bacterial killing was observed but was not fully reproducible when thrombocytes from different donors where used. While interaction of bacteria and thrombocytes was evident in the present study, interaction between antibiotic activity and thrombocytes seems unlikely. Whether variability was caused by different thrombocyte concentrates needs further investigation.

Repeated determination of moxifloxacin concentrations in interstitial space fluid of muscle and subcutis in septic patients

BACKGROUND

For an effective antimicrobial treatment, it is crucial that antibiotics reach sufficient concentrations in plasma and tissue. Currently no data exist regarding moxifloxacin plasma concentrations and exposure levels in tissue under septic conditions.

OBJECTIVES

To determine the pharmacokinetics of moxifloxacin in plasma and interstitial space fluid over a prolonged period.

PATIENTS AND METHODS

Ten septic patients were treated with 400 mg of moxifloxacin once a day; on days 1, 3 and 5 of treatment plasma sampling and microdialysis in the subcutis and muscle of the upper thigh were performed to determine concentrations of moxifloxacin in different compartments. This trial was registered in the German Clinical Trials Register (DRKS, register number DRKS00012985).

RESULTS

Mean unbound fraction of moxifloxacin in plasma was 85.5±3.4%. On day 1, Cmax in subcutis and muscle was 2.8±1.8 and 2.5±1.3 mg/L, respectively, AUC was 24.8±15.1 and 21.3±10.5 mg·h/L, respectively, and fAUC0-24/MIC was 100.9±62.9 and 86.5±38.3 h, respectively. Cmax for unbound moxifloxacin in plasma was 3.5±0.9 mg/L, AUC was 23.5±7.5 mg·h/L and fAUC0-24/MIC was 91.6±24.8 h. Key pharmacokinetic parameters on days 3 and 5 showed no significant differences. Clearance was higher than in healthy adults, but tissue concentrations were comparable, most likely due to a lower protein binding.

CONCLUSIONS

Surprisingly, the first dose already achieved exposure comparable to steady-state conditions. The approved daily dose of 400 mg was adequate in our patient population. Thus, it seems that in septic patients a loading dose on the first day of treatment with moxifloxacin is not required.

A population pharmacokinetic model of intravenous telavancin in healthy individuals to assess tissue exposure

Non-compartmental analysis of telavancin microdialysis data indicated a sustained exposure in soft tissues and that unbound plasma concentrations were underestimated in vitro. The objective of the present evaluation was to develop a population pharmacokinetic model of telavancin to describe its plasma protein binding, its distribution into muscle, and subcutaneous tissue and to predict pharmacokinetic/-dynamic target attainment (PTA). Total plasma concentrations and microdialysate concentrations (plasma, subcutaneous, and muscle tissue) were available up to 24 h (plasma microdialysate, up to 8 h) post-dose from eight healthy subjects after a single intravenous infusion of 10 mg/kg telavancin. Population pharmacokinetic modeling and simulations were performed using NONMEM. A two-compartment model with saturable protein binding best described plasma concentrations. Plasma unbound fractions at steady state were 23, 15, and 11% at 100, 50, and 10% of the maximum predicted concentrations respectively. Distribution into muscle and subcutaneous tissue was non-linear and described appropriately by one additional compartment each. Based on total plasma concentrations, predicted median (95% confidence interval) values of AUC/MIC (MIC 0.125 mg/L, clinical breakpoint for MRSA) at steady state were 4009 [3421-4619] with a PTA of 96 [78-100] %. The fAUC/MIC in muscle was 496 [227-1232] with a PTA of 100 [98-100] %. The %fT_>MIC was approximately 100% in plasma and interstitial space fluid of muscle and subcutaneous tissues up to an MIC of 0.25 mg/L. The model provided a new hypothesis on telavancin plasma protein binding in vivo. Proposed pharmacodynamic targets in plasma and muscle are achieved with currently approved doses of 10 mg/kg daily.

The Antistaphylococcal Lysin, CF-301, Activates Key Host Factors in Human Blood To Potentiate Methicillin-Resistant Staphylococcus aureus Bacteriolysis

Bacteriophage-derived lysins are cell-wall-hydrolytic enzymes that represent a potential new class of antibacterial therapeutics in development to address burgeoning antimicrobial resistance. CF-301, the lead compound in this class, is in clinical development as an adjunctive treatment to potentially improve clinical cure rates of Staphylococcus aureus bacteremia and infective endocarditis (IE) when used in addition to antibiotics. In order to profile the activity of CF-301 in a clinically relevant milieu, we assessed its in vitro activity in human blood versus in a conventional testing medium (cation-adjusted Mueller-Hinton broth [caMHB]). CF-301 exhibited substantially greater potency (32 to ≥100-fold) in human blood versus caMHB in three standard microbiologic testing formats (e.g., broth dilution MICs, checkerboard synergy, and time-kill assays). We demonstrated that CF-301 acted synergistically with two key human blood factors, human serum lysozyme (HuLYZ) and human serum albumin (HSA), which normally have no nascent antistaphylococcal activity, against a prototypic methicillin-resistant S. aureus (MRSA) strain (MW2). Similar in vitro enhancement of CF-301 activity was also observed in rabbit, horse, and dog (but not rat or mouse) blood. Two well-established MRSA IE models in rabbit and rat were used to validate these findings in vivo by demonstrating comparable synergistic efficacy with standard-of-care anti-MRSA antibiotics at >100-fold lower lysin doses in the rabbit than in the rat model. The unique properties of CF-301 that enable bactericidal potentiation of antimicrobial activity via activation of "latent" host factors in human blood may have important therapeutic implications for durable improvements in clinical outcomes of serious antibiotic-resistant staphylococcal infections.

Impact of erythrocytes on bacterial growth and antimicrobial activity of selected antibiotics

It has been shown that protein binding, temperature, and pH influence in vitro pharmacodynamic (PD) models. The fact that corpuscular blood compounds might also have an important impact is something which has, until now, often been neglected. We investigated if the addition of human erythrocytes to standard growth media (Mueller Hinton Broth, MHBII) has an influence on bacterial growth behavior and on antibiotic efficacy. We did this by using bacterial growth assays and time kill curves (TKC) of selected strains (Escherichia coli ATCC25922, Staphylococcus aureus ATCC29213, and Pseudomonas aeruginosa ATCC27853) over 24 h. The final concentration of erythrocytes was set to match the physiological concentrations in the blood of a healthy human, i.e., 3 × 10^6 cells/μl in MHBII. Meropenem, ciprofloxacin, and tigecycline were tested with concentrations several-fold above and below the minimal inhibitory concentration (MIC). Moreover, HPLC analysis of antibiotic stability and distribution in erythrocytes was performed. Meropenem, ciprofloxacin, and tigecycline showed the greatest decline in activity against E. coli when erythrocytes were present. A mean difference in log10 bacterial killing between pure MHBII and 50%-Ery of 3.83, 1.33, and 2.42 was found for ciprofloxacin, meropenem, and tigecycline, respectively. In the case of ciprofloxacin, HPLC analysis revealed that less extracellular antibiotic is available in the presence of erythrocytes. We have demonstrated that erythrocytes do influence antimicrobial activity and that this might have an impact on the extrapolation of in vitro activity testing to in vivo efficacy in patients.

A Population Pharmacokinetic Analysis to Study the Effect of Extracorporeal Membrane Oxygenation on Cefepime Disposition in Children

OBJECTIVES

Limited data exist on the effects of extracorporeal membrane oxygenation on pharmacokinetics of cefepime in critically ill pediatric patients. The objective was to describe cefepime disposition in children treated with extracorporeal membrane oxygenation using population pharmacokinetic modeling.

DESIGN

Multicenter, prospective observational study.

SETTING

The pediatric and cardiac ICUs of six sites of the Collaborative Pediatric Critical Care Research Network.

PATIENTS

Seventeen critically ill children (30 d to < 2 yr old) on extracorporeal membrane oxygenation who received cefepime as standard of care between January 4, 2014, and August 24, 2015, were enrolled.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A pharmacokinetic model was developed to evaluate cefepime disposition differences due to extracorporeal membrane oxygenation. A two-compartment model with linear elimination, weight effects on clearance, intercompartmental clearance (Q), central volume of distribution (V1), and peripheral volume of distribution (V2) adequately described the data. The typical value of clearance in this study was 7.1 mL/min (1.9 mL/min/kg) for a patient weighing 5.8 kg. This value decreased by approximately 40% with the addition of renal replacement therapy. The typical value for V1 was 1,170 mL. In the setting of blood transfusions, V1 increased by over two-fold but was reduced with increasing age of the extracorporeal membrane oxygenation circuit oxygenator.

CONCLUSIONS

Cefepime clearance was reduced in pediatric patients treated with extracorporeal membrane oxygenation compared with previously reported values in children not receiving extracorporeal membrane oxygenation. The model demonstrated that the age of the extracorporeal membrane oxygenation circuit oxygenator is inversely correlated to V1. For free cefepime, only 14 of the 19 doses (74%) demonstrated a fT_minimum inhibitory concentration of 16 mg/L, an appropriate target for the treatment of pseudomonal infections, for greater than 70% of the dosing interval. Pediatric patients on extracorporeal membrane oxygenation might benefit from the addition of therapeutic drug monitoring of cefepime to assure appropriate dosing.

Combination of Antibodies and Antibiotics as a Promising Strategy Against Multidrug-Resistant Pathogens of the Respiratory Tract

The emergence of clinical isolates associated to multidrug resistance is a serious threat worldwide in terms of public health since complicates the success of the antibiotic treatment and the resolution of the infectious process. This is of great concern in pathogens affecting the lower respiratory tract as these infections are one of the major causes of mortality in children and adults. In most cases where the respiratory pathogen is associated to multidrug-resistance, antimicrobial concentrations both in serum and at the site of infection may be insufficient and the resolution of the infection depends on the interaction of the invading pathogen with the host immune response. The outcome of these infections largely depends on the susceptibility of the pathogen to the antibiotic treatment, although the humoral and cellular immune responses also play an important role in this process. Hence, prophylactic measures or even immunotherapy are alternatives against these multi-resistant pathogens. In this sense, specific antibodies and antibiotics may act concomitantly against the respiratory pathogen. Alteration of cell surface structures by antimicrobial drugs even at sub-inhibitory concentrations might result in greater exposure of microbial ligands that are normally hidden or hardly exposed. This alteration of the bacterial envelope may stimulate opsonization by natural and/or specific antibodies or even by host defense components, increasing the recognition of the microbial pathogen by circulating phagocytes. In this review we will explain the most relevant studies, where vaccination or the use of monoclonal antibodies in combination with antimicrobial treatment has demonstrated to be an alternative strategy to overcome the impact of multidrug resistance in respiratory pathogens.

Discovery of a cofactor-independent inhibitor of Mycobacterium tuberculosis InhA

AN12855 is a novel cofactor-independent inhibitor of Mycobacterium tuberculosis InhA. AN12855 has potent activity against M. tuberculosis, good oral bioavailability, and comparable efficacy to isoniazid in infection models.

New antitubercular agents are needed to combat the spread of multidrug- and extensively drug-resistant strains of Mycobacterium tuberculosis. The frontline antitubercular drug isoniazid (INH) targets the mycobacterial enoyl-ACP reductase, InhA. Resistance to INH is predominantly through mutations affecting the prodrug-activating enzyme KatG. Here, we report the identification of the diazaborines as a new class of direct InhA inhibitors. The lead compound, AN12855, exhibited in vitro bactericidal activity against replicating bacteria and was active against several drug-resistant clinical isolates. Biophysical and structural investigations revealed that AN12855 binds to and inhibits the substrate-binding site of InhA in a cofactor-independent manner. AN12855 showed good drug exposure after i.v. and oral delivery, with 53% oral bioavailability. Delivered orally, AN12855 exhibited dose-dependent efficacy in both an acute and chronic murine model of tuberculosis infection that was comparable with INH. Combined, AN12855 is a promising candidate for the development of new antitubercular agents.

In Vitro ADME Properties of Two Novel Antimicrobial Peptoid-Based Compounds as Potential Agents against Canine Pyoderma

Antimicrobial peptides (AMPs) hold promise as the next generation of antimicrobial agents, but often suffer from rapid degradation in vivo. Modifying AMPs with non-proteinogenic residues such as peptoids (oligomers of N-alkylglycines) provides the potential to improve stability. We have identified two novel peptoid-based compounds, B1 and D2, which are effective against the canine skin pathogen Staphylococcus pseudintermedius, the main cause of antibiotic use in companion animals. We report on their potential to treat infections topically by characterizing their release from formulation and in vitro ADME properties. In vitro ADME assays included skin penetration profiles, stability to proteases and liver microsomes, and plasma protein binding. Both B1 and D2 were resistant to proteases and >98% bound to plasma proteins. While half-lives in liver microsomes for both were >2 h, peptoid D2 showed higher stability to plasma proteases than the peptide-peptoid hybrid B1 (>2 versus 0.5 h). Both compounds were suitable for administration in an oil-in-water cream formulation (50% release in 8 h), and displayed no skin permeation, in the absence or presence of skin permeability modifiers. Our results indicate that these peptoid-based drugs may be suitable as antimicrobials for local treatment of canine superficial pyoderma and that they can overcome the inherent limitations of stability encountered in peptides.

Seventy-Five Years of Research on Protein Binding

This review summarizes evidence that the impact of protein binding of the activity of antibiotics is multifaceted and more complex than indicated by the numerical value of protein binding alone. A plethora of studies has proven that protein binding of antibiotics matters, as the free fraction only is antibacterially active and governs pharmacokinetics. Several studies have indicated that independent from protein binding of immunoglobulin G, albumin, α1-acid-glycoprotein, and pulmonary surfactant acted synergistically with antibacterial agents, thus suggesting that some intrinsic properties of serum proteins may have mediated serum-antibiotic synergisms. It has been demonstrated that IgG and albumin permeabilized Gram-negative and Gram-positive bacteria and facilitated the uptake of poorly penetrating antibiotics. Alpha-1-acid-glycoprotein and pulmonary surfactant also exerted a permeabilizing activity, but proof that this property results in a sensitizing effect is missing. The permeabilizing effect of serum proteins may explain why serum-antibiotic synergisms do not represent a general phenomenon but are limited to specific drug-bug associations only. Although evidence has been generated to support the hypothesis that native serum proteins interact synergistically with antibiotics, systematic and well-controlled studies have to be performed to substantiate this phenomenon. The interactions between serum proteins and bacterial surfaces are driven by physicochemical forces. However, preparative techniques, storage conditions, and incubation methods have a significant impact on the intrinsic activities of these serum proteins affecting serum-antibiotic synergisms, so these techniques have to be standardized; otherwise, contradictory data or even artifacts will be generated.

Effect of cardiopulmonary bypass on cytochrome P450 enzyme activity: implications for pharmacotherapy

For patients undergoing cardiopulmonary bypass (CPB) during cardiac surgery, there are well-documented changes in the pharmacokinetics (PK) of commonly administered drugs. Although multiple factors potentially underpin these changes, there has been scant research attention on the impact of CPB to alter the activities of cytochrome P450 (CYP) isoenzymes. PK changes during cardiac surgery with CPB have the potential to adversely affect the safety and efficacy of pharmacotherapy and increase the risk of drug-drug interactions. Clinically significant changes in drug PK during CPB are likely to be prominent for drugs where CYP metabolism is a major clearance (CL) mechanism. However, clinical data from patients undergoing CPB surgery in support of this hypothesis are lacking, leaving a significant knowledge gap. In this review, we address the effects of CPB on the release of pro-inflammatory cytokines, in surgeries with and without CPB, both pre and post initiation of surgery. We reviewed literature to explore the relationship between the release of pro-inflammatory cytokines, and the expression and activities of CYP enzymes. Through this approach, we provide new insight on the effects of CPB on the PK of drugs administered to patients in the clinical setting. Future research to address this knowledge gap will have considerable impact to assist clinicians with optimizing pharmacotherapy in this patient population.

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.

Plasma Protein Binding Structure-Activity Relationships Related to the N-Terminus of Daptomycin

Daptomycin is a lipopeptide antibiotic that is highly bound to plasma proteins. To date, the plasma components and structure-activity relationships responsible for the plasma protein binding profile of daptomycin remain uncharacterized. In the present study we have employed a surface plasmon resonance assay together with molecular docking techniques to investigate the plasma protein binding structure-activity relationships related to the N-terminal fatty acyl of daptomycin. Three compounds were investigated: (1) native daptomycin, which displays an N-terminal n-decanoyl fatty acid side chain, and two analogues with modifications to the N-terminal fatty acyl chain; (2) des-acyl daptomycin; and (3) acetyl-daptomycin. The surface plasmon resonance (SPR) data showed that the binding profile of native daptomycin was in the rank order human serum albumin (HSA) ≫ α-1-antitrypsin > low-density lipoprotein ≥ hemoglobin > sex hormone binding globulin > α-1-acid-glycoprotein (AGP) > hemopexin > fibrinogen > α-2-macroglobulin > β2-microglobulin > high-density lipoprotein > fibronectin > haptoglobulin > transferrin > immunoglobulin G. Notably, binding to fatty acid free HSA was greater than binding to nondelipidated HSA. SPR and ultrafiltration studies also indicated that physiological concentrations of calcium increase binding of daptomycin and acetyl-daptomycin to HSA and AGP. A molecular model of the daptomycin-human serum albumin A complex is presented that illustrates the pivotal role of the N-terminal fatty acyl chain of daptomycin for binding to drug site 1 of HSA. In proof-of-concept, the capacity of physiological cocktails of the identified plasma proteins to inhibit the antibacterial activity of daptomycin was assessed with in vitro microbiological assays. We show that HSA, α-1-antitrypsin, low-density lipoprotein, sex hormone binding globulin, α-1-acid-glycoprotein, and hemopexin are responsible for the majority of the sequestering activity in human plasma. The findings are relevant to medicinal chemistry programs focused on the development of next-generation daptomycin lipopeptides. Tailored modifications to the N-terminal fatty acyl domain of the daptomycin molecule should yield novel daptomycin lipopeptides with more ideal plasma protein binding profiles to increase the levels of active (free) drug in plasma and improved in vivo activity.

Bionano Interaction Study on Antimicrobial Star-Shaped Peptide Polymer Nanoparticles

'Structurally nanoengineered antimicrobial peptide polymers' (SNAPPs), in the form of star-shaped peptide polymer nanoparticles, have been recently demonstrated as a new class of antimicrobial agents with superior in vitro and in vivo efficacy against Gram-negative pathogens, including multidrug-resistant species. Herein, we present a detailed bionano interaction study on SNAPPs by assessing their antimicrobial activities against several Gram-negative bacteria in complex biological matrices. Simulated body fluid and animal serum were used as test media to reveal factors that influence the antimicrobial efficacy of SNAPPs. With the exception of Acinetobacter baumannii, the presence of divalent cations at physiological concentrations reduced the antimicrobial efficacy of SNAPPs from minimum inhibitory concentrations (MICs) within the nanomolar range (40-300 nM) against Escherichia coli, Pseudomanas aeruginosa, and Klebsiella pneumoniae to 0.6-4.7 μM. By using E. coli as a representative bacterial species, we demonstrated that the reduction in activity was due to a decrease in the ability of SNAPPs to cause outer and inner membrane disruption. This effect could be reversed through coadministration with a chelating agent. Interestingly, the potency of SNAPPs against A. baumannii was retained even under high salt concentrations. The presence of serum proteins was also found to affect the interaction of SNAPPs with bacterial membranes, possibly through intermolecular binding. Collectively, this study highlights the need to consider the possible interactions of (bio)molecules present in vivo with any new antimicrobial agent under development. We also demonstrate that outer membrane disruption/destabilization is an important but hitherto under-recognized target for the antimicrobial action of peptide-based agents, such as antimicrobial peptides (AMPs). Overall, the findings presented herein could aid in the design of more efficient peptide-based antimicrobial agents with uncompromised potency even under physiological conditions.

A structure-based model for predicting serum albumin binding

One of the many factors involved in determining the distribution and metabolism of a compound is the strength of its binding to human serum albumin. While experimental and QSAR approaches for determining binding to albumin exist, various factors limit their ability to provide accurate binding affinity for novel compounds. Thus, to complement the existing tools, we have developed a structure-based model of serum albumin binding. Our approach for predicting binding incorporated the inherent flexibility and promiscuity known to exist for albumin. We found that a weighted combination of the predicted logP and docking score most accurately distinguished between binders and nonbinders. This model was successfully used to predict serum albumin binding in a large test set of therapeutics that had experimental binding data.

Importance of relating efficacy measures to unbound drug concentrations for anti-infective agents

For the optimization of dosing regimens of anti-infective agents, it is imperative to have a good understanding of pharmacokinetics (PK) and pharmacodynamics (PD). Whenever possible, drug efficacy needs to be related to unbound concentrations at the site of action. For anti-infective drugs, the infection site is typically located outside plasma, and a drug must diffuse through capillary membranes to reach its target. Disease- and drug-related factors can contribute to differential tissue distribution. As a result, the assumption that the plasma concentration of drugs represents a suitable surrogate of tissue concentrations may lead to erroneous conclusions. Quantifying drug exposure in tissues represents an opportunity to relate the pharmacologically active concentrations to an observed pharmacodynamic parameter, such as the MIC. Selection of an appropriate specimen to sample and the advantages and limitations of the available sampling techniques require careful consideration. Ultimately, the goal will be to assess the appropriateness of a drug and dosing regimen for a specific pathogen and infection.

Protein binding: do we ever learn?

Although the influence of protein binding (PB) on antibacterial activity has been reported for many antibiotics and over many years, there is currently no standardization for pharmacodynamic models that account for the impact of protein binding of antimicrobial agents in vitro. This might explain the somewhat contradictory results obtained from different studies. Simple in vitro models which compare the MIC obtained in protein-free standard medium versus a protein-rich medium are prone to methodological pitfalls and may lead to flawed conclusions. Within in vitro test systems, a range of test conditions, including source of protein, concentration of the tested antibiotic, temperature, pH, electrolytes, and supplements may influence the impact of protein binding. As new antibiotics with a high degree of protein binding are in clinical development, attention and action directed toward the optimization and standardization of testing the impact of protein binding on the activity of antibiotics in vitro become even more urgent. In addition, the quantitative relationship between the effects of protein binding in vitro and in vivo needs to be established, since the physiological conditions differ. General recommendations for testing the impact of protein binding in vitro are suggested.

Pharmacokinetics of Cefovecin in squirrel monkey (Saimiri sciureus), rhesus macaques (Macaca mulatta), and cynomolgus macaques (Macaca fascicularis)

Cefovecin sodium is a third-generation broad-spectrum cephalosporin antibiotic licensed for the treatment of skin infections in cats and dogs. The objective of our study was to assess whether its pharmacokinetic profile in squirrel monkey, rhesus macaques, and cynomolgus macaques was similar to that of dogs. Plasma levels were determined by using protein precipitation followed by liquid chromatography tandem mass spectrometry. After subcutaneous dosing at 8 mg/kg, the plasma terminal half-life of cefovecin was substantially shorter in the nonhuman primates (2.6 to 8.0 h) than in dogs (102 h). The total plasma exposure (AUC(0-96h)) was 10- to 40-fold lower in nonhuman primate species. In cynomolgus macaques, cefovecin showed a similar subcutaneous bioavailability (82% compared with 100%) and volume of distribution (0.16 compared with 0.12 L/kg) as compared to dogs; however, the plasma clearance of cefovecin was 20-fold higher. Cefovecin susceptibility testing and minimum inhibitory concentrations were not established for clinical isolates in nonhuman primates. However, if the minimum inhibitory concentrations of cefovecin for various nonhuman primates pathogens are in the same range as those observed for canine pathogens, our results suggest that cefovecin used at the same dosing regimen and frequency prescribed for the dogs will be ineffective and that increases in dose or frequency (or both) may be required.

Plasma protein binding may reduce antimicrobial activity by preventing intra-bacterial uptake of antibiotics, for example clindamycin

OBJECTIVES

although plasma protein binding (PPB) is accepted to be an essential factor in reducing antimicrobial activity, little is known about the underlying mechanisms. One possibility includes impaired penetration of an antimicrobial into bacterial cells in the presence of PPB. As a prerequisite for testing this hypothesis an optimized medium displaying high protein binding without impairing bacterial growth had to be identified for our model compound clindamycin.

METHODS

determination of PPB, bacterial growth and antimicrobial killing was performed in Mueller-Hinton broth (MHB) containing various amounts of human albumin or serum. [(3)H]clindamycin was used to investigate clindamycin penetration into Staphylococcus aureus.

RESULTS

of all investigated media only MHB(50%serum) and MHB(70%serum) achieved protein binding comparable to pure serum. In contrast, MHB(20%serum) and most media containing only albumin demonstrated considerably lower protein binding. Pure serum resulted in bacterial growth inhibition compared with MHB while MHB(16%albumin) and MHB(50%serum) did not result in significant differences in bacterial count after 24 h. However, in both MHB(16%albumin) and MHB(50%serum) the antimicrobial activity of clindamycin was reduced by >2 log(10) cfu/mL compared with pure MHB. The radioactive signal after administration of [(3)H]clindamycin to S. aureus was significantly decreased in pure serum as well as in MHB(16%albumin) and MHB(50%serum), while no significant difference was observed for MHB(4%albumin) and MHB(20%serum).

CONCLUSIONS

reduction of the intracellular radioactive signal in the presence of serum proteins correlated both with the degree of protein binding and reduction of antimicrobial activity supporting the hypothesis of impairment of activity by PPB by reducing intra-bacterial antimicrobial concentrations.

Human serum binding and its effect on the pharmacodynamics of the lantibiotic MU1140

The degree of MU1140 binding to human serum was measured and the effect of serum on MU1140 pharmacodynamics against Streptococcus pneumoniae and Staphylococcus aureus was investigated. 92.7% ± 2.0% of total MU1140 was bound to serum components as determined by ultrafiltration when tested in the concentration range 6.25-200 μg/ml. MIC and time-kill studies were used to study the effect of serum on the dynamics of MU1140. Serum inhibited MU1140 activity against S. pneumoniae but was found to enhance its activity against S. aureus. This phenomenon has not been reported for any other lantibiotic. Time-kill studies of MU1140 against S. aureus in various concentrations of serum revealed that the greatest bactericidal effect was observed at the lowest serum concentration. Mathematical modeling was used to quantify serum augmentation of MU1140 activity against S. aureus. Serum, at the lowest concentration, was shown to decrease MU1140 EC(50) against S. aureus by an order of magnitude. The data suggests that unbound MU1140 comprise the pharmacologically active fraction. Further, these findings suggest the possible existence of a complex dual inhibition and augmentation effect of serum on MU1140's activity against S. aureus. The molecular mechanism responsible for the synergistic action of human serum on MU1140's activity against S. aureus remains to be elucidated.

Significance of protein binding in pharmacokinetics and pharmacodynamics

The significance of plasma protein binding on drug efficacy and, subsequently, the clinical relevance of changes in protein binding has been controversially discussed for decades. The uncertainty concerning the impact of plasma protein binding on a drug's pharmacological activity is, in part, related to the approach used when investigating and interpreting protein binding effects in vitro and in vivo. Frequently, a generalized one-size-fits-all approach, such as "protein binding does matter/does not matter," may not be applicable. An appropriate analysis requires careful consideration of both pharmacokinetic and pharmacodynamic processes, as they both contribute to the safety and efficacy of drugs. Therefore, the aim of this article is to provide a concise review of the theoretical concepts of protein binding, and to discuss relevant examples where applicable.