Comparison of the pharmacokinetic properties of vancomycin, linezolid, tigecyclin, and daptomycin

Interaction of the Atypical Tetracyclines Chelocardin and Amidochelocardin with Renal Drug Transporters

Antimicrobial resistance is expected to increase mortality rates by up to several million deaths per year by 2050 without new treatment options at hand. Recently, we characterized the pharmacokinetic (PK) and pharmacodynamic properties of two atypical tetracyclines, chelocardin (CHD) and amidochelocardin (CDCHD) that exhibit no cross-resistance with clinically used antibacterials. Both compounds were preferentially renally cleared and demonstrated pronounced effects in an ascending urinary tract infection model against E. coli. Renal drug transporters are known to influence clearance into the urine. In particular, inhibition of apical transporters in renal tubular epithelial cells can lead to intracellular accumulation and potential cell toxicity, whereas inhibition of basolateral transporters can cause a higher systemic exposure. Here, selected murine and human organic cation (Oct), organic anion (Oat), and efflux transporters were studied to elucidate interactions with CHD and CDCHD underlying their PK behavior. CHD exhibited stronger inhibitory effects on mOat1 and mOat3 and their human homologues hOAT1 and hOAT3 compared to CDCHD. While CHD was a substrate of mOat3 and mOct1, CDCHD was not. By contrast, no inhibitory effect was observed on Octs. CDCHD rather appeared to foster enhanced substrate transport on mOct1. CHD and CDCHD inhibited the efflux transporter hMRP2 on the apical side. In summary, the substrate nature of CHD in conjunction with its autoinhibition toward mOat3 rationalizes the distinct urine concentration profile compared to CDCHD that was previously observed in vivo. Further studies are needed to investigate the accumulation in renal tubular cells and the nephrotoxicity risk.

Population pharmacokinetic analysis for dose regimen optimization of vancomycin in Southern Chinese children

Changes in physiological factors may result in large pharmacokinetic variability of vancomycin in pediatric patients, thereby leading to either supratherapeutic or subtherapeutic exposure and potentially affecting clinical outcomes. This study set out to characterize the disposition of vancomycin, quantify the exposure target and establish an optimal dosage regimen among the Southern Chinese pediatric population. Routine therapeutic drug monitoring data of 453 patients were available. We performed a retrospective population pharmacokinetic analysis of hospitalized children prescribed intravenous vancomycin using NONMEM® software. A one-compartment PPK model of vancomycin with body weight and renal functions as covariates based on a cutoff of 2 years old children was proposed in this study. Both internal and external validation showing acceptable and robust predictive performance of the model to estimate PK parameters. The value of area under the curve over 24 h to minimum inhibitory concentration ratio (AUC0-24/MIC) ≥ 260 was a significant predictor for therapeutic efficacy. Monte Carlo simulations served as a model-informed precision dosing approach and suggested that different optimal dose regimens in various scenarios should be considered rather than flat dosing. The evaluation of vancomycin exposure-efficacy relationship indicated that lower target level of AUC0-24/MIC may be needed to achieve clinical effectiveness in children, which was used to derive the recommended dosing regimen. Further prospective studies will be needed to corroborate and elucidate these results.

Updated antimicrobial dosing recommendations for obese patients

The prevalence of obesity has increased considerably in the last few decades. Pathophysiological changes in obese patients lead to pharmacokinetic (PK) and pharmacodynamic (PD) alterations that can condition the correct exposure to antimicrobials if standard dosages are used. Inadequate dosing in obese patients can lead to toxicity or therapeutic failure. In recent years, additional antimicrobial PK/PD data, extended infusion strategies, and studies in critically ill patients have made it possible to obtain data to provide a better dosage in obese patients. Despite this, it is usually difficult to find information on drug dosing in this population, which is sometimes contradictory. This is a comprehensive review of the dosing of different types of antimicrobials (antibiotics, antifungals, antivirals, and antituberculosis drugs) in obese patients, where the literature on PK and possible dosing strategies in obese adults was critically assessed.

Comparative effectiveness of daptomycin versus vancomycin among patients with methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections: A systematic literature review and meta-analysis

BACKGROUND

In the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSIs), vancomycin stands as the prevalent therapeutic agent. Daptomycin remains an alternative antibiotic to treat MRSA BSIs in cases where vancomycin proves ineffective. However, studies have conflicted on whether daptomycin is more effective than vancomycin among patients with MRSA BSI.

OBJECTIVE

To compare the effectiveness of daptomycin and vancomycin for the prevention of mortality among adult patients with MRSA BSI.

METHODS

Systematic searches of databases were performed, including Embase, PubMed, Web of Science, and Cochrane Library. The Newcastle Ottawa Scale (NOS) and Revised Cochrane risk-of-bias tool for randomized trials (RoB 2) were used to assess the quality of individual observational and randomized control studies, respectively. Pooled odd ratios were calculated using random effects models.

RESULTS

Twenty studies were included based on a priori set inclusion and exclusion criteria. Daptomycin treatment was associated with non-significant lower mortality odds, compared to vancomycin treatment (OR = 0.81; 95% CI, 0.62, 1.06). Sub-analyses based on the time patients were switched from another anti-MRSA treatment to daptomycin demonstrated that switching to daptomycin within 3 or 5 days was significantly associated with 55% and 45% decreased odds of all-cause mortality, respectively. However, switching to daptomycin any time after five days of treatment was not significantly associated with lower odds of mortality. Stratified analysis based on vancomycin minimum inhibitory concentration (MIC) revealed that daptomycin treatment among patients infected with MRSA strains with MIC≥1 mg/L was significantly associated with 40% lower odds of mortality compared to vancomycin treatment.

CONCLUSION

Compared with vancomycin, an early switch from vancomycin to daptomycin was significantly associated with lower odds of mortality. In contrast, switching to daptomycin at any time only showed a trend towards reduced mortality, with a non-significant association. Therefore, the efficacy of early daptomycin use over vancomycin against mortality among MRSA BSIs patients may add evidence to the existing literature in support of switching to daptomycin early over remaining on vancomycin. More randomized and prospective studies are needed to assess this association.

Pharmacokinetics in Critically Ill Children with Acute Kidney Injury

Acute kidney injury (AKI) is a commonly encountered comorbidity in critically ill children. The coexistence of AKI disturbs drug pharmacokinetics and pharmacodynamics, leading to clinically significant consequences. This can complicate an already critical clinical scenario by causing potential underdosing or overdosing giving way to possible therapeutic failures and adverse reactions. Current available studies offer little guidance to help maneuver such complex dosing regimens and decision-making in pediatric patients as most of them are done on heterogeneous groups of adult populations. Though there are some studies on drug dosing during continuous renal replacement therapy (CRRT), their utility is in question because of the recent advances in CRRT technology. Our review aims to discuss the principles of pharmacokinetics pertinent for honing the existing practices of drug dosing in critically ill children with AKI, and the various complexities and intricate challenges involved. This in turn will provide a framework to help enable caretakers to tailor dosing regimens in complex clinical setups with further ease and precision.

Dose optimization in surgical prophylaxis: sub-inhibitory dosing of vancomycin increases rates of biofilm formation and the rates of surgical site infection

Antibiotic stewardship is viewed as having great public health benefit with limited direct benefit to the patient at the time of administration. The objective of our study was to determine if inappropriate administration of antibiotics could create conditions that would increase the rates of surgical infection. We hypothesized that sub-MIC levels of vancomycin would increase Staphylococcus aureus growth, biofilm formation, and rates of infection. S. aureus MRSA and MSSA strains were used for all experiments. Bacteria were grown planktonically and monitored using spectrophotometry. Quantitative agar culture was used to measure planktonic and biofilm bacterial burden. A mouse abscess model was used to confirm phenotypes in vivo. In the planktonic growth assay, increases in bacterial burden at ¼ MIC vancomycin were observed in USA300 JE2 by 72 h. Similar findings were observed with ½ MIC in Newman and SH1000. For biofilm formation, USA300 JE2 at ¼ and ½ MIC vancomycin increased biofilm formation by approximately 1.3- and 2.3-fold respectively at 72 h as compared to untreated controls. Similar findings were observed with Newman and SH1000 with a 2.4-fold increase in biofilm formation at ½ MIC vancomycin. In a mouse abscess model, there was a 1.2-fold increase with sub-MIC vancomycin at 3 days post infection. Our study showed that Sub-optimal vancomycin dosing promoted S. aureus planktonic growth and biofilm formation, phenotypic measures of bacterial virulence. This phenotype induced by sub-MIC levels of vancomycin was also observed to increase rates of infection and pathogenesis in our mouse model. Risks of exposure to sub-MIC concentrations with vancomycin in surgical procedures are greater as there is decreased bioavailability in tissue in comparison to other antibiotics. This highlights the importance of proper antibiotic selection, stewardship, and dosing for both surgical prophylaxis and treatment of infection.

Developmental Pharmacokinetics of Antibiotics Used in Neonatal ICU: Focus on Preterm Infants

Neonatal Infections are among the most common reasons for admission to the intensive care unit. Neonatal sepsis (NS) significantly contributes to mortality rates. Empiric antibiotic therapy of NS recommended by current international guidelines includes benzylpenicillin, ampicillin/amoxicillin, and aminoglycosides (gentamicin). The rise of antibacterial resistance precipitates the growth of the use of antibiotics of the Watch (second, third, and fourth generations of cephalosporines, carbapenems, macrolides, glycopeptides, rifamycins, fluoroquinolones) and Reserve groups (fifth generation of cephalosporines, oxazolidinones, lipoglycopeptides, fosfomycin), which are associated with a less clinical experience and higher risks of toxic reactions. A proper dosing regimen is essential for effective and safe antibiotic therapy, but its choice in neonates is complicated with high variability in the maturation of organ systems affecting drug absorption, distribution, metabolism, and excretion. Changes in antibiotic pharmacokinetic parameters result in altered efficacy and safety. Population pharmacokinetics can help to prognosis outcomes of antibiotic therapy, but it should be considered that the neonatal population is heterogeneous, and this heterogeneity is mainly determined by gestational and postnatal age. Preterm neonates are common in clinical practice, and due to the different physiology compared to the full terms, constitute a specific neonatal subpopulation. The objective of this review is to summarize the evidence about the developmental changes (specific for preterm and full-term infants, separately) of pharmacokinetic parameters of antibiotics used in neonatal intensive care units.

Off-label use versus formal recommendations of conventional and novel antibiotics for the treatment of infections caused by multidrug-resistant bacteria

The infections caused by multidrug- and extensively drug-resistant (MDR, XDR) bacteria, including Gram-positive cocci (GPC, including methicillin-resistant Staphylococcus aureus, MDR-Streptococcus pneumoniae and vancomycin-resistant enterococci) and Gram-negative bacilli (GNB, including carbapenem-resistant [CR] Enterobacterales, CR-Pseudomonas aeruginosa and XDR/CR-Acinetobacter baumannii complex) can be quite challenging for physicians with respect to treatment decisions. Apart from complicated urinary tract and intra-abdominal infections (cUTIs, cIAIs), bloodstream infections and pneumonia, these difficult-to-treat bacteria also cause infections at miscellaneous sites (bones, joints, native/prosthetic valves and skin structures, etc.). Antibiotics like dalbavancin, oritavancin, telavancin and daptomycin are currently approved for the treatment of acute bacterial skin and skin structural infections (ABSSSIs) caused by GPC. Additionally, ceftaroline, linezolid and tigecycline have been formally approved for the treatment of community-acquired pneumonia and ABSSSI. Cefiderocol and meropenem-vaborbactam are currently approved for the treatment of cUTIs caused by XDR-GNB. The spectra of ceftazidime-avibactam and imipenem/cilastatin-relebactam are broader than that of ceftolozane-tazobactam, but these three antibiotics are currently approved for the treatment of hospital-acquired pneumonia, cIAIs and cUTIs caused by MDR-GNB. Clinical investigations of other novel antibiotics (including cefepime-zidebactam, aztreonam-avibactam and sulbactam-durlobactam) for the treatment of various infections are ongoing. Nevertheless, evidence for adequate antibiotic regimens against osteomyelitis, arthritis and infective endocarditis due to several GPC and MDR-GNB is still mostly lacking. A comprehensive review of PubMed publications was undertaken and the formal indications and off-label use of important conventional and novel antibiotics against MDR/XDR-GPC and GNB isolates cultured from miscellaneous sites are presented in this paper.

A Brief Review of Pharmacokinetic Assessments of Vancomycin in Special Groups of Patients with Altered Pharmacokinetic Parameters

Vancomycin is considered the drug of choice against many Gram-positive bacterial infections. Therapeutic drug monitoring (TDM) is essential to achieve an optimum clinical response and avoid vancomycin-induced adverse reactions including nephrotoxicity. Although different studies are available on vancomycin TDM, still there are controversies regarding the selection among different pharmacokinetic parameters including trough concentration, the area under the curve to minimum inhibitory concentration ratio (AUC24h/MIC), AUC of intervals, elimination constant, and vancomycin clearance. In this review, different pharmacokinetic parameters for vancomycin TDM have been discussed along with corresponding advantages and disadvantages. Also, vancomycin pharmacokinetic assessments are discussed in patients with altered pharmacokinetic parameters including those with renal and/or hepatic failure, critically ill patients, patients with burn injuries, intravenous drug users, obese and morbidly obese patients, those with cancer, patients undergoing organ transplantation, and vancomycin administration during pregnancy and lactation. An individualized dosing regimen is required to guarantee the optimum therapeutic responses and minimize adverse reactions including acute kidney injury in these special groups of patients. According to the pharmacoeconomic data on vancomycin TDM, pharmacokinetic assessments would be cost-effective in patients with altered pharmacokinetics and are associated with shorter hospitalization period, faster clinical stability status, and shorter courses of inpatient vancomycin administration.

Tissue Penetration of Antimicrobials in Intensive Care Unit Patients: A Systematic Review-Part II

In patients that are admitted to intensive care units (ICUs), the clinical outcome of severe infections depends on several factors, as well as the early administration of chemotherapies and comorbidities. Antimicrobials may be used in off-label regimens to maximize the probability of therapeutic concentrations within infected tissues and to prevent the selection of resistant clones. Interestingly, the literature clearly shows that the rate of tissue penetration is variable among antibacterial drugs, and the correlation between plasma and tissue concentrations may be inconstant. The present review harvests data about tissue penetration of antibacterial drugs in ICU patients, limiting the search to those drugs that mainly act as protein synthesis inhibitors and disrupting DNA structure and function. As expected, fluoroquinolones, macrolides, linezolid, and tigecycline have an excellent diffusion into epithelial lining fluid. That high penetration is fundamental for the therapy of ventilator and healthcare-associated pneumonia. Some drugs also display a high penetration rate within cerebrospinal fluid, while other agents diffuse into the skin and soft tissues. Further studies are needed to improve our knowledge about drug tissue penetration, especially in the presence of factors that may affect drug pharmacokinetics.

Tissue Penetration of Antimicrobials in Intensive Care Unit Patients: A Systematic Review—Part I

The challenging severity of some infections, especially in critically ill patients, makes the diffusion of antimicrobial drugs within tissues one of the cornerstones of chemotherapy. The knowledge of how antibacterial agents penetrate tissues may come from different sources: preclinical studies in animal models, phase I–III clinical trials and post-registration studies. However, the particular physiopathology of critically ill patients may significantly alter drug pharmacokinetics. Indeed, changes in interstitial volumes (the third space) and/or in glomerular filtration ratio may influence the achievement of bactericidal concentrations in peripheral compartments, while inflammation can alter the systemic distribution of some drugs. On the contrary, other antibacterial agents may reach high and effective concentrations thanks to the increased tissue accumulation of macrophages and neutrophils. Therefore, the present review explores the tissue distribution of beta-lactams and other antimicrobials acting on the cell wall and cytoplasmic membrane of bacteria in critically ill patients. A systematic search of articles was performed according to PRISMA guidelines, and tissue/plasma penetration ratios were collected. Results showed a highly variable passage of drugs within tissues, while large interindividual variability may represent a hurdle which must be overcome to achieve therapeutic concentrations in some compartments. To solve that issue, off-label dosing regimens could represent an effective solution in particular conditions.

Pharmacokinetic assessment of vancomycin in critically ill patients and nephrotoxicity prediction using individualized pharmacokinetic parameters

Introduction: Therapeutic drug monitoring (TDM) and pharmacokinetic assessments of vancomycin would be essential to avoid vancomycin-associated nephrotoxicity and obtain optimal therapeutic and clinical responses. Different pharmacokinetic parameters, including trough concentration and area under the curve (AUC), have been proposed to assess the safety and efficacy of vancomycin administration. Methods: Critically ill patients receiving vancomycin at Nemazee Hospital were included in this prospective study. Four blood samples at various time intervals were taken from each participated patient. Vancomycin was extracted from plasma samples and analyzed using a validated HPLC method. Results: Fifty-three critically ill patients with a total of 212 blood samples from June 2019 to June 2021 were included in this study. There was a significant correlation between baseline GFR, baseline serum creatinine, trough and peak concentrations, AUCτ, AUC24h, Cl, and Vd values with vancomycin-induced AKI. Based on trough concentration values, 66% of patients were under-dosed (trough concentration <15 μg/ml) and 18.9% were over-dosed (trough concentration ≥20 μg/ml). Also, based on AUC24h values, about 52.2% were under-dosed (AUC24h < 400 μg h/ml), and 21.7% were over-dosed (AUC24h > 600 μg h/ml) that emphasizes on the superiority of AUC-based monitoring approach for TDM purposes to avoid nephrotoxicity occurrence. Conclusion: The AUC-based monitoring approach would be superior in terms of nephrotoxicity prediction. Also, to avoid vancomycin-induced AKI, trough concentration and AUCτ values should be maintained below the cut-off points.

Comparing the pharmacokinetics and organ/tissue distribution of anti-methicillin-resistant Staphylococcus aureus agents using a rat model of sepsis

Sepsis is a major cause of death, and sepsis-derived physiological changes complicate the understanding of drug distribution in organs/tissues, which determines the efficacy and toxicity of antimicrobial agents. In this study, we evaluated and compared the pharmacokinetics of methicillin-resistant Staphylococcus aureus treatment agents in sepsis with that of vancomycin, arbekacin, linezolid, and daptomycin.Rat models of sepsis were prepared using cecal ligation puncture. The pharmacokinetics of vancomycin, arbekacin, linezolid, and daptomycin were evaluated using their drug concentration profiles in plasma, kidneys, liver, lungs, skin, and muscles after intravenous administration in normal and septic rats.The kidney/plasma concentration ratio was higher in septic rats than in normal rats for vancomycin, arbekacin, and daptomycin but not for linezolid. The increase in the kidney/plasma concentration ratio for vancomycin was time-dependent, indicating an association between sepsis and stasis of vancomycin in the kidneys. In contrast, the distribution of linezolid from the blood to the organs/tissues in septic rats was comparable to that in normal rats.Sepsis-induced nephrotoxicity results in the stasis of vancomycin in the kidney, suggesting that this exacerbates proximal tubular epithelial cell injury. No dose modification of linezolid may be required for patients with sepsis.

Occurrence, detection and ecotoxicity studies of selected pharmaceuticals in aqueous ecosystems- a systematic appraisal

Pharmaceutical compounds (PCs) have globally emerged as a significant group of environmental contaminants due to the constant detection of their residues in the environment. The main scope of this review is to fill the void of information on the knowledge on the African occurrence of selected PCs in environmental matrices in comparison with those outside Africa and their respective toxic actions on both aquatic and non-aquatic biota through ecotoxicity bioassays. To achieve this objective, the study focused on commonly used and detected pharmaceutical drugs (residues). Based on the conducted literature survey, Africa has the highest levels of ciprofloxacin, sulfamethoxazole, lamivudine, acetaminophen, and diclofenac while Europe has the lowest of all these PC residues in her physical environments. For ecotoxicity bioassays, the few data available are mostly on individual groups of pharmaceuticals whereas there is sparsely available data on their combined forms.

Factors Associated with Daptomycin-Induced Eosinophilic Pneumonia

The risk factors for eosinophilic pneumonia (EP) remain unclear. We investigate the characteristics of patients with daptomycin (DAP)-induced EP and conducted a retrospective observational study. A total of 450 patients aged ≥ 18 years who received DAP (25 DAP with EP, 425 DAP without EP) were included. The median duration from the first DAP administration to EP onset was 18.0 days. Definite, probable, and possible DAP-induced EP were diagnosed in 0, 9, and 16 patients, respectively. The median age (DAP with EP, 72.0 years; DAP without EP, 64.0 years), DAP dosage/body weight (BW) (9.00 vs. 7.50 mg/kg), blood eosinophil count (cells/μL) (419 vs. 96), and the percentage of hemodialyzed patients (40.0% vs. 13.4%) were significantly higher in patients with EP than in patients without EP in the univariate analysis. In separate multivariate logistic regression analyses, age (odds ratio (OR), 1.03; 95% confidence interval (CI), 1.00–1.05), DAP dosage/BW (OR, 1.61; 95% CI, 1.25–2.07), and hemodialysis (OR, 4.42; 95% CI, 1.86–10.5) were significantly associated with DAP-induced EP. Clinicians may need to consider the potential factors associated with EP, especially in older patients, patients on hemodialysis, or patients who receive > 9.00 mg/kg of DAP.

Digestive Decolonization of Colorectal Carriage of Vancomycin-resistant Enterococcus faecium in a Japanese Adult

Patients with vancomycin-resistant Enterococcus (VRE) colonization should be managed in an isolation room with contact precautions. We herein report a patient whose colorectal carriage of VRE was successfully decolonized using concomitant bowel irrigation with polyethylene glycol, probiotics, and oral antimicrobials, linezolid and orally-administered daptomycin, for release from isolation and contact precautions. We therefore would like to suggest a potential strategy for managing patients with VRE colonization.

Antibacterial and antioxidant activity of cinnamon essential oil-laden 45S5 bioactive glass/soy protein composite scaffolds for the treatment of bone infections and oxidative stress

This study aimed to fabricate cinnamon essential oil (CO)-laden 45S5 bioactive glass (BG)/soy protein (SP) scaffolds exhibiting antioxidant and antibacterial activity. In this regard, 45S5 BG-based scaffolds were produced by the foam replica method, and subsequently the scaffolds were coated with various concentrations of CO (2.5, 5 and 7 (v/v) %) incorporated SP solution. Scanning electron microscopy images revealed that the CO-laden SP effectively attached to the 45S5 BG scaffold struts. The presence of 45S5 BG, SP and CO was confirmed using Fourier transform infrared spectroscopy. Compressive strength results indicated that SP based coatings improved the scaffolds' mechanical properties compared to uncoated BG scaffolds. The loading efficiency and releasing behaviour of the different CO concentrations were tested by gas chromatography-mass spectroscopy and UV-Vis spectroscopy. The results showed that CO incorporated scaffolds have controlled releasing behaviour over seven days. Furthermore, the coating on the scaffold surfaces slightly retarded, but it did not inhibit, the in vitro bioactivity of the scaffolds. Moreover, the antioxidant and antibacterial activity of CO was studied. The free radical scavenging activity measured by DPPH was 5 ± 1, 41 ± 3, 44 ± 1 and 43 ± 1 % for BGSP, CO2.5, CO5 and CO7, respectively. The antioxidant activity was thus enhanced by incorporating CO. Agar diffusion and colony counting results indicated that the incorporation of CO increased the antibacterial activity of scaffolds against S. aureus and E. coli. In addition, cytotoxicity of the scaffolds was investigated using MG-63 osteoblast-like cells. The results showed that the BG-SP scaffold was non-toxic under the investigated conditions, whereas dose-dependent toxicity was observed in CO-laden scaffolds. Considered together, the developed phytotherapeutic agent laden 45S5 BG-based scaffolds are promising for bone tissue engineering exhibiting capability to combat bone infections and to protect against oxidative stress damage.

Efficacy of tigecycline alone or in combination for experimental infections by KPC carbapenemase-producing Klebsiella pneumoniae

Although in vitro data suggest that tigecycline is active against Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp), experimental and clinical data are limited. We studied the effect of tigecycline alone or in combination for experimental infections by KPC-Kp. A total of 540 male C57BL/6 mice were infected with three genetically diverse KPC-Kp isolates susceptible to tigecycline with meropenem minimum inhibitory concentrations (MICs) of 4, 16 and 256 μg/mL, respectively. Mice were randomly treated with water for injection, tigecycline, meropenem and colistin alone, and double or triple combinations of tigecycline, colistin and meropenem. Mouse survival was recorded for 14 days. In separate experiments, mice were sacrificed 6 h and 24 h after bacterial challenge for quantitative culture of tissues and serological analysis. Time-kill curves were performed. Tigecycline, colistin and meropenem concentrations were measured in tissues and serum by high-performance liquid chromatography (HPLC). Survival was significantly prolonged when mice were treated with tigecycline alone and tigecycline-containing regimens compared with control mice and mice treated with tigecycline-sparing regimens. Tigecycline-sparing regimens were active only against the isolate with a meropenem MIC of 4 μg/mL. Mortality was associated with progression to multiple organ failure. Tigecycline and tigecycline-containing regimens achieved a rapid decrease of bacterial loads both in tissues and in vitro. Tigecycline concentrations in tissues were negatively correlated with tissue bacterial load. Tigecycline alone or in combination with meropenem and/or colistin achieves effective treatment of experimental KPC-Kp infections irrespective of the meropenem MIC.

A meta-analysis of bone cement mediated antibiotic release: Overkill, but a viable approach to eradicate osteomyelitis and other infections tied to open procedures

A number of clinical studies have highlighted the success of antibiotics formulated at concentrations between 0 and 6% w/w into bone cements to address localized infections. Separately, some commercial manufacturers have produced gentamycin-infused bone cement mixtures as a countermeasure to infection. The anecdotal evidence suggests that antibiotic infused cements can help eradicate or delay the onset of infections. Quantifying the functionality of that response is more challenging. We have surveyed the literature to identify studies in which controlled drug release or mechanical behavioral assessments have been conducted on drug-infused cements. The focus here is on vancomycin (VAN) in part due to its higher potency relative to gentamycin and its more common usage for staph infections. Takeaways from the limited pool of research studies indicate that large fractions (>99%) of the infused vancomycin remain sequestered in the cement and aren't bioavailable after solidification. Antibiotic fluence ranged from 1 to 283 μg/cm²hr. The initial strength of the various antibiotic loaded samples as produced were 52-96 MPa. Simulated exposures in a fluid environment by submersion reduced the antibiotic loaded strengths between 3 and 29%. Some strength measurements were noted below the ASTM F451 standard for acrylic bone cement although drug releasing spacers likely have different requirements. The glassy behavior of the cured cement led to both vancomycin and gentamicin having low permeability and a burst response. Smaller drug molecules and more gel-like immobilization matrices with lower glass transition temperatures offer higher potential for larger and more comprehensive drug bioavailability.

The impact of continuous renal replacement therapy on antibiotic pharmacokinetics in critically ill patients

Introduction: Mortality due to severe infections in critically ill patients undergoing continuous renal replacement therapy (CRRT) remains high. Nevertheless, rapid administration of adequate antibiotic therapy can improve survival. Delivering optimized antibiotic therapy can be a challenge, as standard drug regimens often result in insufficient or excessive serum concentrations due to significant changes in the volume of distribution and/or drug clearance in these patients. Insufficient drug concentrations can be responsible for therapeutic failure and death, while excessive concentrations can cause toxic adverse events.Areas covered: We performed a narrative review of the impact of CRRT on the pharmacokinetics of the most frequently used antibiotics in critically ill patients. We have provided explanations for the changes in the PKs of antibiotics observed and suggestions to optimize dosage regimens in these patients.Expert opinion: Despite considerable efforts to identify optimal antibiotic dosage regimens for critically ill patients receiving CRRT, adequate target achievement remains too low for hydrophilic antibiotics in many patients. Whenever possible, individualized therapy based on results from therapeutic drug monitoring must be given to avoid undertreatment or toxicity.

Model-Informed Drug Development for Anti-Infectives: State of the Art and Future

Model-informed drug development (MIDD) has a long and rich history in infectious diseases. This review describes foundational principles of translational anti-infective pharmacology, including choice of appropriate measures of exposure and pharmacodynamic (PD) measures, patient subpopulations, and drug-drug interactions. Examples are presented for state-of-the-art, empiric, mechanistic, interdisciplinary, and real-world evidence MIDD applications in the development of antibacterials (review of minimum inhibitory concentration-based models, mechanism-based pharmacokinetic/PD (PK/PD) models, PK/PD models of resistance, and immune response), antifungals, antivirals, drugs for the treatment of global health infectious diseases, and medical countermeasures. The degree of adoption of MIDD practices across the infectious diseases field is also summarized. The future application of MIDD in infectious diseases will progress along two planes; "depth" and "breadth" of MIDD methods. "MIDD depth" refers to deeper incorporation of the specific pathogen biology and intrinsic and acquired-resistance mechanisms; host factors, such as immunologic response and infection site, to enable deeper interrogation of pharmacological impact on pathogen clearance; clinical outcome and emergence of resistance from a pathogen; and patient and population perspective. In particular, improved early assessment of the emergence of resistance potential will become a greater focus in MIDD, as this is poorly mitigated by current development approaches. "MIDD breadth" refers to greater adoption of model-centered approaches to anti-infective development. Specifically, this means how various MIDD approaches and translational tools can be integrated or connected in a systematic way that supports decision making by key stakeholders (sponsors, regulators, and payers) across the entire development pathway.

Daptomycin for the successful treatment of postoperative methicillin-resistant Staphylococcus aureus empyema: a case report

Empyema is typically treated using pleural space drainage and systemic treatment with antimicrobials, and specific antimicrobial agents in the case of methicillin-resistant Staphylococcus aureus (MRSA) infections. A 57-year-old man underwent segmental resection of the left lung owing to multiple lung metastases and developed MRSA-related empyema postoperatively. Although the patient received chest drainage and linezolid, the inflammation caused by the infection persisted. Consequently, linezolid was replaced by daptomycin, and his empyema was accordingly resolved. Our findings indicate that daptomycin could be an effective treatment for postoperative MRSA-related empyema.

Differential effects of antibiotics on neutrophils exposed to lipoteichoic acid derived from Staphylococcus aureus

BACKGROUND

Persistent bacteremia occurs in at least 30% of patients with Staphylococcus aureus bloodstream infection (SAB) and may be attributable to a dysregulated host immune response. Neutrophils interact with a variety of S. aureus microbial factors, including lipoteichoic acid (LTA), to activate phagocytic function in a concentration-dependent manner. Antibiotics have been shown to exert both direct antimicrobial action as well as immunomodulatory effects. In this study, we compared the effects of different anti-staphylococcal antibiotics on LTA-mediated immune activation of neutrophils.

METHODS

Neutrophils obtained from healthy volunteers were exposed to two levels of LTA (1 and 10 μg/ml) with or without addition of antibiotics from different pharmacologic classes (vancomycin, daptomycin, ceftaroline). Neutrophil function was assessed by examining phagocytic response, activation (CD11b, CD62L expression), Toll-like receptor-2 expression, cell survival and apoptosis, and CXCL8 release.

RESULTS

Differential LTA-mediated antibiotic effects on neutrophil function were observed primarily at the high LTA exposure level. Ceftaroline in the presence of 10 μg/ml LTA had the most prominent effects on phagocytosis and CD11b and CD62L expression, with trends towards increased neutrophil survival and preservation of CXCL8 release when compared to daptomycin and vancomycin with the latter significantly dampening PMN CXCL8 release.

CONCLUSIONS

Select antimicrobial agents, such as ceftaroline, exert immunostimulatory effects on neutrophils exposed to S. aureus LTA, which when confirmed in vivo, could be leveraged for its dual immunomodulatory and antibacterial actions for the treatment of persistent SAB mediated by a dysregulated host response.

Comparison of In Vivo Transportability of Anti-Methicillin-Resistant Staphylococcus aureus (MRSA) Agents Into Intracellular and Extracellular Tissue Spaces in Rats

The pathogenic bacterium Staphylococcus aureus can penetrate host cells. However, intracellular S. aureus is not considered during antimicrobial agent selection in clinical chemotherapy because of the lack of information about drug transportability into cells in vivo. We focused on agents used to treat methicillin-resistant S. aureus (MRSA) (vancomycin, arbekacin, linezolid, and daptomycin) and indirectly assessed the drug levels in intracellular compartment using plasma, tissue homogenates, and interstitial fluid (ISF) samples from the skin of rats using the microneedle array technique. Lower drug levels were observed in the ISF than in the plasma for daptomycin but extracellular and intracellular drug levels were comparable. In contrast, vancomycin, arbekacin, and linezolid showed higher concentrations in the ISF than in the plasma. Intracellular transport was estimated only for arbekacin. Stasis of vancomycin in the ISF was also observed. These results suggest that both low vancomycin exposure against intracellular S. aureus infection and long-term subinhibitory drug levels in the ISF contribute to the failure of treatment and emergence of antibiotic resistance. Based on its pharmacokinetic characteristics in niche extravascular tissue spaces, arbekacin may be suitable for achieving sufficient clinical outcomes for MRSA infection because the drug is widely distributed in extracellular and intracellular compartments.

The pharmacokinetic/pharmacodynamic paradigm for antimicrobial drugs in veterinary medicine: Recent advances and critical appraisal

Pharmacokinetic/pharmacodynamic (PK/PD) modelling is the initial step in the semi-mechanistic approach for optimizing dosage regimens for systemically acting antimicrobial drugs (AMDs). Numerical values of PK/PD indices are used to predict dose and dosing interval on a rational basis followed by confirmation in clinical trials. The value of PK/PD indices lies in their universal applicability amongst animal species. Two PK/PD indices are routinely used in veterinary medicine, the ratio of the area under the curve of the free drug plasma concentration to the minimum inhibitory concentration (MIC) (fAUC/MIC) and the time that free plasma concentration exceeds the MIC over the dosing interval (fT > MIC). The basic concepts of PK/PD modelling of AMDs were established some 20 years ago. Earlier studies have been reviewed previously and are not reconsidered in this review. This review describes and provides a critical appraisal of more recent, advanced PK/PD approaches, with particular reference to their application in veterinary medicine. Also discussed are some hypotheses and new areas for future developments.First, a brief overview of PK/PD principles is presented as the basis for then reviewing more advanced mechanistic considerations on the precise nature of selected indices. Then, several new approaches to selecting PK/PD indices and establishing their numerical values are reviewed, including (a) the modelling of time-kill curves and (b) the use of population PK investigations. PK/PD indices can be used for dose determination, and they are required to establish clinical breakpoints for antimicrobial susceptibility testing. A particular consideration is given to the precise nature of MIC, because it is pivotal in establishing PK/PD indices, explaining that it is not a "pharmacodynamic parameter" in the usual sense of this term.

Efficacy and mechanism of actions of natural antimicrobial drugs

Microbial infections have significantly increased over the last decades, and the mortality rates remain unacceptably high. The emergence of new resistance patterns and the spread of new viruses challenge the eradication of infectious diseases. The declining efficacy of antimicrobial drugs has become a global public health problem. Natural products derived from natural sources, such as plants, animals, and microorganisms, have significant efficacy for the treatment of infectious diseases accompanied by less adverse effects, synergy, and ability to overcome drug resistance. As the Chinese female scientist Youyou Tu received the Nobel Prize for the antimalarial drug artemisinin, antimicrobial drugs developed from Traditional Chinese Medicine are expected to receive increasing attention again. This review summarizes the antimicrobial agents derived from natural products approved for nearly 20 years and describes their efficacy and mode of action. The aim of this unit is to review the current status of antimicrobial drugs from natural products in order to increase the value of natural products as a source of novel drug candidates for infectious diseases.

Assessment of antibacterial activity of levonadifloxacin against contemporary gram-positive clinical isolates collected from various Indian hospitals using disk-diffusion assay

Objectives

Levonadifloxacin is a novel benzoquinolizine subclass of quinolone with broad-spectrum activities against problematic pathogens such as methicillin-resistant Staphylococcus aureus, quinolone-resistant S. aureus, vancomycin intermediate S. aureus, and vancomycin-resistant S. aureus. Levonadifloxacin and its oral prodrug, alalevonadifloxacin, have been recently approved in India for the treatment of acute bacterial skin and skin structure infections, including concurrent bacteraemia and diabetic foot infections. The aim of the study is to assess the activity of levonadifloxacin against Gram-positive clinical isolates collected from various Indian hospitals using the disc-diffusion method.

Materials and Methods

Nonduplicate isolates of S. aureus and other Gram-positive isolates collected from June 2019 to March 2020 were subjected to levonadifloxacin susceptibility testing (disk diffusion method) as per the Clinical and Laboratory Standards Institute guidelines (Year 2019). Levonadifloxacin 10 μg impregnated disks were used during the testing.

Results

A total of 664 diverse Gram-positive clinical isolates collected from six different hospitals in India were analyzed. Majority (65.5%) of the isolates were S. aureus. All the S. aureus and other Gram-positive isolates were found to be susceptible to levonadifloxacin as per the prespecified interpretive criteria identified based on population pharmacokinetic model and Monte Carlo simulation enabled probability of pharmacodynamic target attainment analysis.

Conclusions

The present study showed that levonadifloxacin was highly active against contemporary Gram-positive pathogens and furthermore demonstrated that levonadifloxacin susceptibilities can be reliably determined using the disc-diffusion method.

Pharmacokinetic evaluation of linezolid administered intravenously in obese patients with pneumonia

OBJECTIVES

Altered linezolid pharmacokinetics (PK) in obese individuals has been hypothesized in previous studies. However, specific dosing recommendations for this population are still lacking. The main goal of this study was to evaluate PK/pharmacodynamic (PKPD) target attainment when using a 600 mg intravenous q12h linezolid dose against MRSA in obese patients with pneumonia.

METHODS

Fifteen obese pneumonia patients with a confirmed or suspected MRSA involvement treated with 600 mg of intravenous linezolid q12h were studied for 3 days. Population PK modelling was used to characterize the PK variability and to screen for influential patient characteristics. Monte Carlo simulations were carried out to investigate the PTA and time to target attainment for linezolid dosing against MRSA.

RESULTS

A two-compartment model with linear elimination adequately described the data. Body weight and age both have a significant effect on linezolid clearance. Simulations demonstrate that the probability of attaining PKPD targets is low. Moreover, the PTA decreases with weight, and increases with age. Standard linezolid dosing in obese pneumonia patients with MRSA (MICs of 1-4 mg/L) leads to unacceptably low (near zero to 60%) PTA for patients <65 years old.

CONCLUSIONS

Standard linezolid dosing is likely to provide insufficient target attainment against MRSA in obese patients. Body weight and especially age are important characteristics to be considered when administering linezolid to treat MRSA infections.

The effect of body mass index and creatinine clearance on serum trough concentration of vancomycin in adult patients

Background

The aim of this study was to evaluate the influence of patient body mass index (BMI) and estimated creatinine clearance (CrCl) on serum vancomycin concentrations to define a possible optimal dosage regimen in overweight patients based on data obtained during therapeutic drug monitoring.

Methods

This retrospective study used data collected from January 2017 to January 2019. Adult patients (n = 204) received vancomycin treatment at a dose of 1000 mg every 12 h and underwent serum monitoring. Data collected included patient disease category, sex, age, height, weight, vancomycin concentrations, and serum creatinine. The CrCl values were estimated using the Cockcroft-Gault formula. In this study, statistical comparisons were performed on the results of patients according to serum vancomycin concentration.

Results

Serum vancomycin concentration was significantly related to BMI (P <  0.001) and CrCl (P <  0.05) in adult patients. Furthermore, the trough serum vancomycin concentration showed a logarithmic correlation with BMI (R = − 0.5108, 95% CI: − 0.6082 to − 0.3982, P <  0.001) and CrCl (R = − 0.5739, 95% CI: − 0.6616 to − 0.4707, P <  0.001). The multivariate analysis showed that BMI and CrCl are independent contributors to the trough vancomycin concentration. Moreover, some of the patients with higher BMI (≥ 24 kg/m²) met the goal trough concentration after an adjustment from 1000 mg every 12 h to 1000 mg every 8 h.

Conclusions

Serum vancomycin concentration decreases progressively with increasing BMI and the augmentation in CrCl in adult patients. The trough concentration of vancomycin should be continuously monitored for patients with a BMI ≥ 24 kg/m², and the dosage regimen should be adjusted to reach the target trough concentration in these patients to reduce the impact of BMI.

Current role of oxazolidinones and lipoglycopeptides in skin and soft tissue infections

PURPOSE OF REVIEW

An increase of skin and soft tissue infections involving Staphylococcus aureus has been reported in community and hospital settings. Methicillin resistance in S. aureus is associated with treatment failure and increased mortality. Recently, new antimicrobials with enhanced activity against methicillin-resistant Staph. aureus have been approved for the treatment of skin and soft tissue infections. Among these, novel oxazolidinones and lipoglycopeptides represent options with favorable pharmacokinetic characteristics and safety profiles.

RECENT FINDINGS

Newly approved compounds include tedizolid, characterized by the availability of both oral and intravenous formulation and once daily administration and dalbavancin, a long-acting antimicrobial allowing for weekly administration. These new molecules present advantages, such as enhanced activity against multidrug-resistant Gram-positive bacteria and favorable safety profiles.

SUMMARY

We have reviewed the pharmacokinetic characteristics and the implications for use in skin and soft tissue infections of tedizolid and dalbavancin. Advantages associated with the use of these compounds include the possibility for early patient discharge, reduced hospital length of stay, and outpatient treatment, with potential impact on morbidity, mortality, and overall health-care costs.

Intrathecal Antibacterial and Antifungal Therapies

Intrathecal administration of anti-infectives is indicated in central nervous system infections by multiresistant pathogens when drugs that can reach adequate cerebrospinal fluid (CSF) concentrations by systemic therapy are not available. Antibiotics that readily pass the blood-brain and blood-CSF barriers and/or that have low toxicity allowing an increase in the daily dosage should not be used for intrathecal therapy. Intrathecal therapy is accompanied by systemic treatment. Antibacterials indispensable for intrathecal therapy include aminoglycosides, colistin, daptomycin, tigecycline, and vancomycin. Limited experience suggests the utility of the antifungals amphotericin B and caspofungin. Intraventricular administration ensures distribution throughout the CSF compartment, whereas intralumbar dosing often fails to attain adequate antibiotic concentrations in the ventricles. The individual dose is determined by the estimated size of the CSF space and by the estimated clearance from CSF. For moderately lipophilic anti-infectives with a molecular weight above approximately 1,000 g/mol, as well as for hydrophilic drugs with a molecular weight above approximately 400 g/mol, one daily dose is normally adequate. The ventricular drain should be clamped for 15 to 120 min to facilitate the distribution of the anti-infective in the CSF space. Therapeutic drug monitoring of the trough levels is necessary only in cases of therapeutic failure.

First Report of the Local Spread of Vancomycin-Resistant Enterococci Ascribed to the Interspecies Transmission of a vanA Gene Cluster-Carrying Linear Plasmid

Increasing multidrug resistance, including vancomycin resistance, in enterococci is a major concern in clinical settings. Horizontal gene transfer, such as via plasmids, has been shown to play a crucial role in the acquisition of vancomycin resistance. Among vancomycin resistance types, the VanA type is one of the most prevalent, and outbreaks caused by VanA-type vancomycin-resistant enterococci (VRE) have occurred worldwide. Here, we describe an enterococcal linear plasmid responsible for multispecies local spread of VanA-type VRE. Such a study is important because although hospital outbreaks caused by mixed enterococcal species have been reported, this particular spread indicates plasmid transfer across species. This is a crucial finding because the high risk for such a spread of antimicrobial resistance calls for regular monitoring and surveillance.

Vancomycin-resistant enterococci pose a threat in the clinical setting and have been linked to hospital outbreaks worldwide. In 2017, a local spread of VanA-type vancomycin-resistant enterococci (VRE) occurred in Japan, and 25 enterococcal isolates, including 14 Enterococcus faecium, 8 E. raffinosus, and 3 E. casseliflavus isolates, were identified from four inpatients. Molecular analysis of the multispecies of VanA-type VRE revealed the involvement of both the dissemination of clonally related VRE strains between patients and the horizontal transfer of plasmids harboring the vanA gene cluster between Enterococcus spp. Pulsed-field gel electrophoresis showed that the plasmid DNAs without S1 nuclease treatment were able to migrate into the gel, suggesting that the topology of the plasmid was linear. Whole-genome sequencing revealed that this plasmid, designated pELF2, was 108,102 bp long and encoded multiple antimicrobial resistance genes, including ermA and ant(9). The amino acid sequences of putative replication- and transfer-related genes were highly conserved between pELF2 and pELF1, the latter of which was the first identified enterococcal conjugative linear plasmid. On comparing the genomic structure, pELF2 showed the presence of a backbone similar to that of pELF1, especially with respect to the nucleotide sequences of both terminal ends, indicating a hybrid-type linear plasmid, possessing two different terminal structures. pELF2 possessed a broad host range and high conjugation frequencies for enterococci. The easy transfer of pELF2 to different Enterococcus spp. in vitro might explain this local spread of multiple species, highlighting the clinical threat from the spread of antimicrobial resistance by an enterococcal linear plasmid.

IMPORTANCE Increasing multidrug resistance, including vancomycin resistance, in enterococci is a major concern in clinical settings. Horizontal gene transfer, such as via plasmids, has been shown to play a crucial role in the acquisition of vancomycin resistance. Among vancomycin resistance types, the VanA type is one of the most prevalent, and outbreaks caused by VanA-type vancomycin-resistant enterococci (VRE) have occurred worldwide. Here, we describe an enterococcal linear plasmid responsible for multispecies local spread of VanA-type VRE. Such a study is important because although hospital outbreaks caused by mixed enterococcal species have been reported, this particular spread indicates plasmid transfer across species. This is a crucial finding because the high risk for such a spread of antimicrobial resistance calls for regular monitoring and surveillance.

Population pharmacokinetics and dosing considerations of daptomycin in critically ill patients undergoing continuous renal replacement therapy

Objectives

The dosing regimen of daptomycin for critically ill patients undergoing continuous renal replacement therapy (CRRT) remains controversial. The goal of this study was to provide guidance for optimal daptomycin therapy in CRRT patients with Staphylococcus aureus infections.

Methods

Individual concentration data of 32 CRRT subjects pooled from previously published studies were used to construct the population pharmacokinetic model for daptomycin. Model-based simulations were performed to evaluate the efficacy and risk of toxicity for daptomycin doses of 4, 6 and 8 mg/kg, q24h or q48h, under CRRT doses of 25, 30 and 35 mL/h/kg. Efficacy was assessed by the bacteriostatic and bactericidal AUC/MIC targets and drug exposure-based efficacy references. Toxicity was estimated by safety exposure references and the trough concentration threshold.

Results

A two-compartment model adequately described the pharmacokinetics of daptomycin. Efficacy analysis demonstrated that q48h dosing is associated with an extremely low probability of bactericidal target attainment on every second day after dosing and q24h dosing is preferred for a high probability of bactericidal target attainment. Toxicity evaluation showed that 8 mg/kg q24h has a high probability for reaching the toxicity-related concentration threshold, while 6 mg/kg q24h gives a satisfactory risk–benefit balance. The studied CRRT doses had a limited impact on efficacy and a CRRT dose of 30–35 mL/h/kg may lower the risk of toxicity.

Conclusions

The model predicted that the combination of 6 mg/kg q24h daptomycin dose and CRRT dose of 30–35 mL/h/kg would achieve the best balance of efficacy and safety.

Time-kill curves of daptomycin and Monte Carlo simulation for the treatment of bacteraemia caused by Enterococcus faecium

OBJECTIVES

The aim of this study was to investigate the effect of daptomycin against vancomycin-resistant Enterococcus faecium bacteraemia using computer modelling.

METHODS

Data obtained in vitro from time-kill curves were evaluated by PK/PD modelling and Monte Carlo simulations to determine the logarithmic reduction in the number of colony-forming units (CFU)/mL over 18 days of daptomycin treatment at 6, 8, and 10 mg/kg doses every 24 or 48 h and with variations in creatinine clearance (CL_CR) of 15-29, 30-49, and 50-100 mL/min/1.73 m². Monte Carlo simulations were performed to evaluate the probability of target attainment (PTA) for an area under the unbound drug concentration-time curve/minimum inhibitory concentration (fAUC/MIC) > 36 at the same doses and CL_CR.

RESULTS

Static time-kill model was employed to investigate the antibacterial efficacy of constant daptomycin concentrations. The time-kill curve analysis was performed using mathematical modelling based on a Hill coefficient factor. There was an expressive reduction (> 2 Log CFU/mL) over 18 days of daptomycin treatment in 75th percentile of individuals with CL_CR of 15-100 mL/min/1.73 m²) with daptomycin 6-10 mg/kg/day, except for daptomycin every 48 h. Using fAUC/MIC > 36, PTA was > 90% at MICs ≤ 2 μg/mL.

CONCLUSIONS

Higher daptomycin doses were associated with higher mortality in time-kill curves. The simulations indicated that independent of the CL_CR the therapeutic responses of VRE occur with doses of daptomycin ≥ 6 mg/kg/day and daptomycin every 48 h is insufficient to treat enterococcal bacteraemia.

Describing vancomycin serum levels in pediatric intensive care unit (ICU) patients: are expected goals being met

BACKGROUND

In the pediatric population, infections by methicillin-resistant Staphylococcus aureus (MRSA) are associated with significant morbidity and hospital costs. Vancomycin is a glycopeptide antibiotic, widely used for the treatment of serious infections by Gram-positive microorganisms, especially MRSA. It is recommended to keep the serum level of vancomycin between 10 and 20 mg/L, that correlates with AUC/MIC > 400 in adults. This pharmacodynamic target is extrapolated to pediatric patients despite the lack of similar evidence. However, recent studies suggest that serum levels between 7 and 10 mg/L are predictive of reaching the pharmacodynamic target in this population. In spite of widespread use, ideal information about dosage for the pediatric population remains limited.

METHODS

A retrospective study was conducted in patients admitted to the Pediatric Intensive Care Unit during the period between January 01, 2008 to December 31, 2014. We investigated variables such as age, positive fluid balance and use of vasoactive drugs on the ability of these patients to achieve the proposed recommended serum level target and the vancomycin serum levels.

RESULTS

Our study showed that only 26% of children reached the 10-20 mg/L serum level whereas the 7-20 mg/L serum level was reached by 51% of patients.

CONCLUSIONS

We observed no evidence of a significant association between the inadequacy of serum level and age. The positive fluid balance also had no influence on the vancomycin serum level but patients using vasoactive drugs had a greater serum level adequacy than patients not using vasoactive drugs.

Simple LC-MS/MS Methods Using Core-Shell Octadecylsilyl Microparticulate for the Quantitation of Total and Free Daptomycin in Human Plasma

BACKGROUND

Daptomycin, a cyclic lipopeptide antibiotic, displays high plasma protein binding. This study developed the simple method of liquid chromatographic separation using a core-shell octadecylsilyl microparticulate coupled to tandem mass spectrometry for the quantitation of total and free daptomycin in human plasma.

METHODS

Free daptomycin in plasma was obtained by centrifugal ultrafiltration. Deproteinized plasma specimens were directly separated using a core-shell octadecylsilyl microparticulate with isocratic elution. The mass spectrometer was run in positive-ion electrospray ionization mode. This method was applied to the quantitation of plasma samples in patients treated with intravenous daptomycin.

RESULTS

Daptomycin and diazepam as an internal standard were eluted with a total run time of 10 minutes. The calibration curves of total and free daptomycin in human plasma were linear over the concentration ranges of 1-100 and 0.1-10 mcg/mL, respectively. The lower limits of quantitation of the total and free daptomycin in human plasma were 1.0 and 0.1 mcg/mL, respectively. Their extraction recovery rates in nonfiltrated and ultrafiltrated plasma samples were 106.1% and 98.2%, respectively. Total and free daptomycin did not exhibit any matrix effects in human plasma. The intraday and interday accuracies and imprecisions of total daptomycin were 88.7%-106.0% and 98.7%-105.9%, and within 4.1% and 10.4%, whereas those of free daptomycin were 86.8%-101.6% and 103.0%-107.8%, and within 14.6% and 14.6%, respectively. The plasma concentration ranges of total and free daptomycin in 15 infected patients were 3.01-34.1 and 0.39-3.64 mcg/mL, respectively. The plasma protein binding rate of daptomycin ranged from 80.8% to 94.9%.

CONCLUSIONS

The present simple method with an acceptable analytical performance can be helpful for monitoring the pharmacokinetics of daptomycin in infected patients observed in clinical settings.

Intervertebral disc penetration by antibiotics used prophylactically in spinal surgery: implications for the current standards and treatment of disc infections

PURPOSE

The presence of Propionibacterium acnes in a substantial component of resected disc specimens obtained from patients undergoing discectomy or microdiscectomy has led to the suggestion that this prominent human skin and oral commensal may exacerbate the pathology of degenerative disc disease. This hypothesis, therefore, raises the exciting possibility that antibiotics could play an important role in treating this debilitating condition. To date, however, little information about antibiotic penetration into the intervertebral disc is available.

METHODS

Intervertebral disc tissue obtained from 54 microdiscectomy patients given prophylactic cefazolin (n = 25), clindamycin (n = 17) or vancomycin (n = 12) was assayed by high-performance liquid chromatography, with cefaclor as an internal standard, to determine the concentration of antibiotic penetrating into the disc tissue.

RESULTS

Intervertebral disc tissues from patients receiving the positively charged antibiotic clindamycin contained a significantly greater percentage of the antibacterial dose than the tissue from patients receiving negatively charged cefazolin (P < 0.0001) and vancomycin, which has a slight positive charge (P < 0.0001).

CONCLUSION

Positively charged antibiotics appear more appropriate for future studies investigating potential options for the treatment of low-virulence disc infections. These slides can be retrieved under Electronic Supplementary Material.

Rifabutin Acts in Synergy and Is Bactericidal with Frontline Mycobacterium abscessus Antibiotics Clarithromycin and Tigecycline, Suggesting a Potent Treatment Combination

Mycobacterium abscessus is a rapidly emerging mycobacterial pathogen causing dangerous pulmonary infections. Because these bacteria are intrinsically multidrug resistant, treatment options are limited and have questionable efficacy. The current treatment regimen relies on a combination of antibiotics, including clarithromycin paired with amikacin and either imipenem or cefoxitin. Tigecycline may be added when triple therapy is ineffective. We initially screened a library containing the majority of clinically available antibiotics for anti-M. abscessus activity. The screen identified rifabutin, which was then investigated for its interactions with M. abscessus antibiotics used in drug regimens. Combination of rifabutin with either clarithromycin or tigecycline generated synergistic anti-M. abscessus activity, dropping the rifabutin MIC below concentrations found in the lung. Importantly, these combinations generated bactericidal activity. The triple combination of clarithromycin, tigecycline, and rifabutin was also synergistic, and clinically relevant concentrations had a sterilizing effect on M. abscessus cultures. We suggest that combinations including rifabutin should be further investigated for treatment of M. abscessus pulmonary infections.

Evaluation of Vancomycin Dosing in Patients With Cirrhosis: Beginning De-Liver-ations about a New Nomogram

Background: Reduced hepatic production of creatinine precursors in patients with decompensated cirrhosis leads to falsely low serum creatinine values. Therefore, when performing empiric dosing of vancomycin, an overestimation of creatinine clearance may result in significantly supratherapeutic vancomycin levels and increased risks of nephrotoxicity. Objective: The objective of the study is to evaluate vancomycin dosing requirements in patients with cirrhosis stratified by Child-Pugh Score, with subsequent comparison with doses that are recommended in the previously published and validated Kullar nomogram. Methods: A retrospective evaluation of patients with cirrhosis who received vancomycin for at least 3 full days and had at least 1 serum concentration drawn. Vancomycin daily dose and corresponding serum concentration were collected with patients stratified by Child-Pugh Score for comparison. Each patient had their vancomycin dose compared with the dose suggested by a published nomogram. Results: A total of 201 courses of vancomycin were followed. There were no significant differences between the Child-Pugh cohorts with respect to initial vancomycin dosing. There was also no significant difference in the median initial vancomycin trough concentration between the 3 cohorts (Child-Pugh A: 13.7 µg/mL [interquartile range, IQR: 10.4-22.1]; Child-Pugh B: 20.2 µg/mL [IQR: 15.1-25.9]; Child-Pugh C: 19.3 µg/mL [IQR: 14.9-25.2, P = .08]. The median vancomycin dose using the Kullar nomogram would have been 3.0 g/day (IQR: 2.0-3.75, P < .001), but the median dose actually used in this patient population was significantly less at 2.0 g/day. Nonetheless, the median vancomycin trough concentration in the entire patient population was 19.8 µg/mL (IQR: 15.4-25.9). Conclusion: In patients with cirrhosis, there was a high incidence of supratherapeutic vancomycin serum concentrations despite the fact that dosing was significantly less than that suggested by the published Kullar nomogram.

Impact of cefazolin co-administration with vancomycin to reduce development of vancomycin-intermediate Staphylococcus aureus

OBJECTIVE

Development of antimicrobial resistance during monotherapy of complicated methicillin-resistant Staphylococcus aureus bacteremia is problematic due to cross-resistance between vancomycin (VAN) and daptomycin, the only approved agents for this condition. Our objective was to demonstrate that development of resistance under conditions of suboptimal VAN (200 mg q 12 h) exposure in S. aureus can be attenuated by addition of cefazolin (CFZ).

METHODS

Two strains of S. aureus, 1 methicillin-susceptible Staphylococcus aureus (MSSA) (RN9120) and 1 methicillin-resistant S. aureus (MRSA) (JH1), were evaluated. The organisms were exposed to subtherapeutic VAN concentrations in a 1-compartment pharmacokinetic/pharmacodynamic model combined with recycling in the presence and absence of CFZ. Changes in MIC to glyco/lipopeptides and β-lactams along with susceptibility to human cathelicidin LL-37 killing were studied. Population analysis profiles (PAPs) were performed to detect changes in VAN heteroresistance.

RESULTS

VAN MIC of both organisms increased from 1 to 4 mg/L within 144 h under subtherapeutic VAN exposure. Increase in VAN MIC was associated with increased glyco/lipopeptides MICs. Additionally, increased survival in LL-37 killing assays from 40% to >90% accompanied the increase in VAN MIC. Addition of CFZ prevented the emergence of VAN-intermediate S. aureus. PAPs demonstrated an attenuation of VAN area under the curve shift (reduced organism selection with higher MICs values) when suboptimal VAN exposure was accompanied with CFZ compared to VAN alone (MSSA 17.81 versus 36.027, MRSA -0.35 versus 17.92, respectively). Given the emerging data on the clinical benefits of β-lactam adjunctive therapy in refractory MRSA bacteremia, additional studies on a larger collection of clinical isolates are needed to establish the utility of VAN plus CFZ for treatment of MRSA bacteremia.

Impact of Experimental Variables on the Protein Binding of Tigecycline in Human Plasma as Determined by Ultrafiltration

Tigecycline, a tetracycline derivative, shows atypical plasma protein binding behavior. The unbound fraction decreases with increasing concentration at therapeutic concentrations. Moreover, uncertainty exists about the magnitude of tigecyline's protein binding in man. Unbound fractions between 2.5% and 35% have been reported in plasma from healthy volunteers, and between 25% and 100% in patients, respectively. In the present study, the protein binding of tigecycline has been investigated by ultrafiltration using different experimental conditions. Whereas temperature had only a marginal influence, the unbound fraction at 0.3/3.0 mg/L was low at pH 8.2 (9.4%/1.9%) or in unbuffered pooled plasma (6.3%/1.2%), compared with plasma buffered with HEPES to pH 7.4 (65.9%/39.7%). In experiments with phosphate buffer and EDTA, the concentration dependency was markedly attenuated or abolished, which is compatible with a cooperative binding mechanism involving divalent cations such as calcium. The unbound fraction in clinical plasma samples from patients treated with tigecycline was determined to 66.3 ± 13.7% at concentrations <0.3 mg/L compared with 41.3 ± 16.0% at >1 to <5 mg/L. To summarize, tigecycline appears to be only moderately bound to plasma proteins as determined by ultrafiltration, when a physiological pH is maintained.

Diet-Induced Obesity Does Not Alter Tigecycline Treatment Efficacy in Murine Lyme Disease

Obese individuals more frequently suffer from infections, as a result of increased susceptibility to a number of bacterial pathogens. Furthermore, obesity can alter antibiotic treatment efficacy due to changes in drug pharmacokinetics which can result in under-dosing. However, studies on the treatment of bacterial infections in the context of obesity are scarce. To address this research gap, we assessed efficacy of antibiotic treatment in diet-induced obese mice infected with the Lyme disease pathogen, Borrelia burgdorferi. Diet-induced obese C3H/HeN mice and normal-weight controls were infected with B. burgdorferi, and treated during the acute phase of infection with two doses of tigecycline, adjusted to the weights of diet-induced obese and normal-weight mice. Antibiotic treatment efficacy was assessed 1 month after the treatment by cultivating bacteria from tissues, measuring severity of Lyme carditis, and quantifying bacterial DNA clearance in ten tissues. In addition, B. burgdorferi-specific IgG production was monitored throughout the experiment. Tigecycline treatment was ineffective in reducing B. burgdorferi DNA copies in brain. However, diet-induced obesity did not affect antibiotic-dependent bacterial DNA clearance in any tissues, regardless of the tigecycline dose used for treatment. Production of B. burgdorferi-specific IgGs was delayed and attenuated in mock-treated diet-induced obese mice compared to mock-treated normal-weight animals, but did not differ among experimental groups following antibiotic treatment. No carditis or cultivatable B. burgdorferi were detected in any antibiotic-treated group. In conclusion, obesity was associated with attenuated and delayed humoral immune responses to B. burgdorferi, but did not affect efficacy of antibiotic treatment.

Assessment of linezolid prescriptions in three French hospitals

The use of linezolid to treat gram-positive cocci infections is increasing in France. Linezolid is approved in pneumonia and complicated skin and soft tissue infections. Overuse and misuse of linezolid can favor the emergence and spreading of linezolid-resistant strains. We aimed to assess the appropriateness of linezolid use in French hospitals. This is a multicenter, retrospective study conducted in three tertiary care hospitals. Appropriateness of linezolid indications and adequacy (composite score concerning dosage, route of administration and blood monitoring) were assessed. Over a three-month period, all prescriptions of linezolid were extracted and analyzed by two independent infectious disease experts. Among the 81 initial prescriptions that were evaluated, indication was appropriate in 48% of cases. Among those, 51% complied with international guidelines. Fifty-seven percent of the prescriptions were adequate regarding dosage, route of administration and blood monitoring. Overall, 23% of prescriptions combined both appropriateness and adequacy. The most frequent reasons for inappropriateness were the possibility of choosing narrower-spectrum antibiotics and the empirical use of linezolid in severe sepsis or septic shock. Initial treatment was the most frequently appropriate in bone and joint infection cases (p = 0.001). Our study shows that even if modalities of use were mostly correct, appropriateness of linezolid indications is low. Educational programs are mandatory to improve practices, as well as clinical studies to better assess the efficacy and safety of linezolid in clinical situations other than pneumonia or complicated skin and soft tissue infections.

Daptomycin: Physicochemical, Analytical, and Pharmacological Properties

Daptomycin is the first approved member of a new class of antimicrobials, the cyclic lipopeptides, and presents selective action against gram-positive bacteria, including methicillin- and vancomycin-resistant strains. Considering that resistance to daptomycin is rare, the drug has become very important for current clinical practice. This review covers daptomycin's physicochemical characteristics, antibacterial spectrum, mechanism of action, pharmacokinetics, clinical applications, side effects, drug interactions, and the analytical methods used to measure daptomycin in pharmaceutical products and biologic samples. Special attention has been given to therapeutic drug monitoring reports, as studies have shown its highly variable pharmacokinetics in specific circumstances, such as in patients suffering from critical illness, morbid obesity, severe sepsis, and kidney injury. For the same reason, methods described for therapeutic drug monitoring of daptomycin in the special patient population have been reviewed. In addition, the review presents a discussion of environmentally friendly analytical methods for daptomycin, which are necessary to reduce the impact of our activities on the environment. However, it was observed that there is a gap in the literature in this regard and further research involving the development of "green" methodologies for the analysis of daptomycin is necessary. The review will be useful to the clinical community in assisting with the responsible use of daptomycin, which is critical to prevent the emergence of resistant strains.

Tigecycline Is Highly Efficacious against Mycobacterium abscessus Pulmonary Disease

Mycobacterium abscessus causes chronic pulmonary infections that are extremely difficult to cure. The currently recommended combination therapy is associated with high failure rates and relapse. Tigecycline has been explored in salvage regimens, with a response rate of 43% in those who received at least a month of therapy. We performed a dose-response study in a hollow-fiber system model of pulmonary M. abscessus infection in which we recapitulated tigecycline human pulmonary concentration-time profiles of 8 different doses for 21 days. We identified the maximal kill or efficacy in CFU per milliliter and the ratio of the 0- to 24-h area under the concentration-time curve to MIC (AUC/MIC) associated with 80% efficacy (EC80). The tigecycline efficacy was 5.38 ± 2.35 log10 CFU/ml, and the drug achieved the unprecedented feat of a bacterial level of 1.0 log10 CFU/ml below the pretreatment inoculum (1-log kill) of M. abscessus in the hollow-fiber system. The EC80 AUC/MIC ratio was 36.65, while that for a 1-log kill was 44.6. Monte Carlo experiments with 10,000 patients were used to identify the clinical dose best able to achieve the EC80 or 1-log kill. The standard dose of 100 mg/day had a cumulative fraction of response of 51% for the EC80 and 46% for 1-log kill. For both the EC80 target and 1-log kill, the optimal tigecycline clinical dose was identified as 200 mg/day. The susceptibility breakpoint was ≤0.5 mg/liter. Tigecycline is the most active single agent evaluated to date, and we propose that 200 mg/day be examined as the backbone of new combination therapy regimens to replace current treatment.

Effects of vancomycin, daptomycin, and tigecycline on coagulase-negative staphylococcus biofilm and bacterial viability within biofilm: an in vitro biofilm model

Bacteria may hide in a hydrated polysaccharide matrix known as a biofilm. The structure of the bacterial biofilm renders phagocytosis difficult and increases antibiotic resistance. We hypothesized that repeated doses of antibiotics have an effect on bacteria within the biofilm and that it could inhibit or eradicate biofilm formation. Two clinical biofilm-positive coagulase-negative staphylococcus isolates were evaluated. The effects of antibiotics on preformed and nascent biofilm and on bacterial eradication within the biofilm were determined using different doses of vancomycin, daptomycin, and tigecycline for different durations in an in vitro biofilm model. Vancomycin neither penetrated the biofilm nor had any microbicidal effect on bacteria within the biofilm. Daptomycin had a microbicidal effect on bacteria within the biofilm but had no effect on biofilm inhibition and eradication (independent from dose and treatment time). Tigecycline inhibited and eradicated biofilm formation and had a microbicidal effect on bacteria within the biofilm. In conclusion, (i) biofilm formation appeared to be a major barrier to vancomycin activity, (ii) daptomycin had an antimicrobial effect on the bacteria within the biofilm but not on the biofilm burden, and (iii) tigecycline had effects both on bacteria within the biofilm and on biofilm burden. Thus, both tigecycline and daptomycin might be promising candidates for the treatment of biofilm infections.

Daptomycin: an evidence-based review of its role in the treatment of Gram-positive infections

Infections caused by Gram-positive pathogens remain a major public health burden and are associated with high morbidity and mortality. Increasing rates of infection with Gram-positive bacteria and the emergence of resistance to commonly used antibiotics have led to the need for novel antibiotics. Daptomycin, a cyclic lipopeptide with rapid bactericidal activity against a wide range of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus, has been shown to be effective and has a good safety profile for the approved indications of complicated skin and soft tissue infections (4 mg/kg/day), right-sided infective endocarditis caused by S. aureus, and bacteremia associated with complicated skin and soft tissue infections or right-sided infective endocarditis (6 mg/kg/day). Based on its pharmacokinetic profile and concentration-dependent bactericidal activity, high-dose (>6 mg/kg/day) daptomycin is considered an important treatment option in the management of various difficult-to-treat Gram-positive infections. Although daptomycin resistance has been documented, it remains uncommon despite the increasing use of daptomycin. To enhance activity and to minimize resistance, daptomycin in combination with other antibiotics has also been explored and found to be beneficial in certain severe infections. The availability of daptomycin via a 2-minute intravenous bolus facilitates its outpatient administration, providing an opportunity to reduce risk of health care-associated infections, improve patient satisfaction, and minimize health care costs. Daptomycin, not currently approved for use in the pediatric population, has been shown to be widely used for treating Gram-positive infections in children.