Pulmonary disposition of antimicrobial agents: in vivo observations and clinical relevance

Bronchopulmonary disposition of IV cefepime/taniborbactam (2-0.5 g) administered over 2 h in healthy adult subjects

INTRODUCTION

Taniborbactam (formerly VNRX-5133) is an investigational β-lactamase inhibitor in clinical development in combination with cefepime for the treatment of MDR Gram-negative pathogens.

OBJECTIVES

To assess the safety profile and pulmonary disposition of 2-0.5 g cefepime/taniborbactam administered as a 2 h IV infusion every 8 h following three doses in healthy adult subjects.

METHODS

In this Phase 1 trial, open-label study, plasma samples were collected over the last dosing interval, and subjects (n = 20) were randomized to undergo bronchoalveolar lavage (BAL) at four timepoints after the last dose. Drug concentrations in plasma (total and free as determined by protein binding), BAL fluid and alveolar macrophages (AM) were determined by LC-MS/MS, and the urea correction method was used to calculate epithelial lining fluid (ELF) drug concentrations. Pharmacokinetic parameters were estimated by non-compartmental analysis.

RESULTS

Mean (±SD) taniborbactam Cmax and AUC0-8 in plasma were 24.1 ± 4.1 mg/L and 81.9 ± 13.9 mg·h/L, respectively. Corresponding values for cefepime were 118.4 ± 29.7 mg/L and 346.7 ± 71.3 mg·h/L. Protein binding was 0% for taniborbactam and 22.4% for cefepime. Mean taniborbactam concentrations (mg/L) at 2, 4, 6 and 8 h were 3.9, 1.9, 1.0 and 0.3 in ELF and 12.4, 11.5, 14.3 and 14.9 in AM, with corresponding AUC0-8 ELF of 13.8 and AUC0-8 AM of 106.0 mg·h/L. Cefepime AUC0-8 ELF was 77.9 mg·h/L. No serious adverse events were observed.

CONCLUSION

The observed bronchopulmonary exposures of taniborbactam and cefepime can be employed to design optimal dosing regimens for clinical trials in patients with pneumonia.

Pharmacokinetic/Pharmacodynamic Optimization of Hospital-Acquired and Ventilator-Associated Pneumonia: Challenges and Strategies

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are correlated with high mortality rates worldwide. Thus, the administration of antibiotic therapy with appropriate dosing regimen is critical. An efficient antibiotic is needed to maintain an adequate concentration at the infection site, for a sufficient period of time, to achieve the best therapeutic outcome. It can, however, be challenging for antibiotics to penetrate the pulmonary system due to the complexity of its structure. Crossing the blood alveolar barrier is a difficult process determined by multiple factors that are either drug related or infection related. Thus, the understanding of pharmacokinetics/pharmacodynamics (PK/PD) of antibiotics identifies the optimum dosing regimens to achieve drug penetration into the epithelial lining fluid at adequate therapeutic concentrations. Critically ill patients in the ICU can express augmented renal clearance (ARC), characterized by enhanced renal function, or may have renal dysfunction necessitating supportive care such as continuous renal replacement therapy (CRRT). Both ARC and CRRT can alter drug elimination, thus affecting drug concentrations. PK of critically ill patients is less clear due to the multiple variabilities associated with their condition. Therefore, conventional dosing regimens often lead to therapeutic failure. Another major hurdle faced in optimizing treatment for HAP/VAP is the reduction of the in vitro potency. Therapeutic drug monitoring (TDM), if available, may allow health care providers to personalize treatment to maximize efficacy of the drug exposures while minimizing toxicity. TDM can be of significant importance in populations whom PK are less defined and for resistant infections to achieve the best therapeutic outcome.

Intracellular Accumulation of Novel and Clinically Used TB Drugs Potentiates Intracellular Synergy

The therapeutic repertoire for tuberculosis (TB) remains limited despite the existence of many TB drugs that are highly active in in vitro models and possess clinical utility. Underlying the lack of efficacy in vivo is the inability of TB drugs to penetrate microenvironments inhabited by the causative agent, Mycobacterium tuberculosis, including host alveolar macrophages. Here, we determined the ability of the phenoxazine PhX1 previously shown to be active against M. tuberculosis in vitro to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. We also investigated the extent of permeation into uninfected and M. tuberculosis-infected human macrophage-like Tamm-Horsfall protein 1 (THP-1) cells directly and by comparing to results obtained in vitro in synergy assays. Our data indicate that PhX1 (4,750 ± 127.2 ng/ml) penetrates more effectively into THP-1 cells than do the clinically used anti-TB agents, rifampin (3,050 ± 62.9 ng/ml), moxifloxacin (3,374 ± 48.7 ng/ml), bedaquiline (4,410 ± 190.9 ng/ml), and linezolid (770 ± 14.1 ng/ml). Compound efficacy in infected cells correlated with intracellular accumulation, reinforcing the perceived importance of intracellular penetration as a key drug property. Moreover, we detected synergies deriving from redox-stimulatory combinations of PhX1 or clofazimine with the novel prenylated amino-artemisinin WHN296. Finally, we used compound synergies to elucidate the relationship between compound intracellular accumulation and efficacy, with PhX1/WHN296 synergy levels shown to predict drug efficacy. Collectively, our data support the utility of the applied assays in identifying in vitro active compounds with the potential for clinical development. IMPORTANCE This study addresses the development of novel therapeutic compounds for the eventual treatment of drug-resistant tuberculosis. Tuberculosis continues to progress, with cases of Mycobacterium tuberculosis (M. tuberculosis) resistance to first-line medications increasing. We assess new combinations of drugs with both oxidant and redox properties coupled with a third partner drug, with the focus here being on the potentiation of M. tuberculosis-active combinations of compounds in the intracellular macrophage environment. Thus, we determined the ability of the phenoxazine PhX1, previously shown to be active against M. tuberculosis in vitro, to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. In addition, the extent of permeation into human macrophage-like THP-1 cells and H37Rv-infected THP-1 cells was measured via mass spectrometry and compared to in vitro two-dimensional synergy and subsequent intracellular efficacy. Collectively, our data indicate that development of new drugs will be facilitated using the methods described herein.

Plasma and Intrapulmonary Concentrations of Cefepime and Zidebactam following Intravenous Administration of WCK 5222 to Healthy Adult Subjects

WCK 5222 is a combination of cefepime and the novel β-lactam enhancer zidebactam being developed for the treatment of serious Gram-negative bacterial infections. The objective of this study was to compare plasma (total), epithelial lining fluid (ELF), and alveolar macrophage (AM) concentrations of cefepime and zidebactam in healthy adult subjects. The WCK 5222 dosing regimen was 2 g cefepime/1 g zidebactam administered as a 1-h intravenous infusion every 8 h for a total of 7 doses. Subjects were assigned to one bronchoalveolar lavage (BAL) sampling time at 0.5, 1.25, 3, 6, 8, or 10 h after the seventh dose. Noncompartmental pharmacokinetic parameters were determined from serial plasma concentrations collected over 8-hour and 10-hour intervals following the first and seventh doses, respectively. Penetration ratios were calculated from the area under the plasma concentration-time curve from 0 to 8 h (AUC_0-8) for plasma, ELF, and AM using mean and median concentrations at each BAL sampling time. The plasma maximum concentration of drug (C_max) and AUC values of cefepime and zidebactam increased by 8% to 9% after the seventh versus the first dose of WCK 5222. The respective AUC_0-8 values based on mean concentrations of cefepime and zidebactam in ELF were 127.9 and 52.0 mg · h/liter, and 87.9 and 13.2 mg · h/liter in AM. The ELF to total plasma penetration ratios of cefepime and zidebactam based on mean AUC_0-8 values were 0.39 and 0.38, respectively. The AM to total plasma ratios were 0.27 and 0.10, respectively. The observed plasma, ELF, and AM concentrations of cefepime and zidebactam support studies of WCK 5222 for treatment of pneumonia caused by susceptible pathogens.

Intrapulmonary Pharmacokinetics of Relebactam, a Novel β-Lactamase Inhibitor, Dosed in Combination with Imipenem-Cilastatin in Healthy Subjects

This phase I study assessed the intrapulmonary pharmacokinetic profiles of relebactam (MK-7655), a novel β-lactamase inhibitor, and imipenem. Sixteen healthy subjects received 250 mg relebactam with 500 mg imipenem-cilastatin, given intravenously every 6 h for 5 doses, and were randomized to bronchoscopy/bronchoalveolar lavage at 0.5, 1, 1.5, or 3 h after the last dose (4 subjects per time point). Both drugs penetrated the epithelial lining fluid (ELF) to a similar degree, with the profiles being similar in shape to the corresponding plasma profiles and with the apparent terminal half-lives in plasma and ELF being 1.2 and 1.3 h, respectively, for relebactam and 1.0 h in both compartments for imipenem. The exposure (area under the concentration-time curve from time zero to infinity) in ELF relative to that in plasma was 54% for relebactam and 55% for imipenem, after adjusting for protein binding. ELF penetration for relebactam was further analyzed by fitting the data to a two-compartment pharmacokinetic model to capture its behavior in plasma, with a partitioning coefficient capturing its behavior in the lung compartment. In this model, the time-invariant partition coefficient for relebactam was found to be 55%, based on free drug levels. These results support the clinical evaluation of relebactam with imipenem-cilastatin for the treatment of bacterial pneumonia.

Intrapulmonary Pharmacokinetics of Levonadifloxacin following Oral Administration of Alalevonadifloxacin to Healthy Adult Subjects

Alalevonadifloxacin (WCK 2349) is a novel l-alanine ester prodrug of levonadifloxacin that is being developed as an oral fluoroquinolone antibiotic. The primary objective of this study was to determine and compare plasma, epithelial lining fluid (ELF), and alveolar macrophage (AM) concentrations of levonadifloxacin following oral administration of alalevonadifloxacin to healthy adult subjects. Levonadifloxacin concentrations in plasma, ELF, and AM samples from 30 healthy subjects were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) following oral dosing of alalevonadifloxacin (1,000 mg twice daily for 5 days). Six subjects were assigned to each bronchoalveolar lavage (BAL) fluid sampling time, i.e., 2, 4, 6, 8, or 12 h after the ninth oral dose. Noncompartmental pharmacokinetic (PK) parameters were determined from serial total plasma concentrations collected over a 12-h interval following the first and ninth oral doses. Penetration ratios were calculated from the areas under the concentration-time curves from 0 to 12 h (AUC_0-12) for plasma, ELF, and AM by using mean (and median) concentrations at each BAL sampling time. Unbound plasma concentrations (∼85% plasma protein binding) were used to determine site-to-plasma penetration ratios. Plasma PK parameter values for levonadifloxacin were similar after the first and ninth doses. The respective AUC_0-12 values based on mean ELF and AM concentrations were 172.6 and 35.3 mg · h/liter, respectively. The penetration ratios for ELF and AM levonadifloxacin concentrations to unbound plasma levonadifloxacin concentrations were 7.66 and 1.58, respectively. Similar penetration ratios were observed with median concentrations. The observed plasma, ELF, and AM concentrations of levonadifloxacin support further studies of alalevonadifloxacin for treatment of lower respiratory tract bacterial infections caused by susceptible pathogens. (This study has been registered at ClinicalTrials.gov under identifier NCT02253342.).

Considerations for effect site pharmacokinetics to estimate drug exposure: concentrations of antibiotics in the lung

Bronchoalveolar lavage (BAL) and microdialysis have become the most reliable and relevant methods for measuring lung concentrations of antibiotics, with the majority of BAL studies involving either healthy adult subjects or patients undergoing diagnostic bronchoscopy. Emphasis on the amount of drug that reaches the site of infection is increasingly recognized as necessary to determine whether a dose selection will translate to good clinical outcomes in the treatment of patients with pneumonia. Observed concentrations and/or parameters of exposure (e.g. area-under-the-curve) need to be incorporated with pharmacokinetic-pharmacodynamic indices so that rational dose selection can be identified for specific pathogens and types of pneumonic infection (community-acquired vs hospital-acquired bacterial pneumonia, including ventilator-associated bacterial pneumonia). Although having measured plasma or lung concentration-time data from critically ill patients to incorporate into pharmacokinetic-pharmacodynamic models is very unlikely during drug development, it is essential that altered distribution, augmented renal clearance, and renal or hepatic dysfunction should be considered. Notably, the number of published studies involving microdialysis and intrapulmonary penetration of antibiotics has been limited and mainly involve beta-lactam agents, levofloxacin, and fosfomycin. Opportunities to measure in high-resolution effect site spatial pharmacokinetics (e.g. with MALDI-MSI or PET imaging) and in vivo continuous drug concentrations (e.g. with aptamer-based probes) now exist. Going forward these studies could be incorporated into antibiotic development programs for pneumonia in order to further increase the probability of candidate success.

Comparison of Omadacycline and Tigecycline Pharmacokinetics in the Plasma, Epithelial Lining Fluid, and Alveolar Cells of Healthy Adult Subjects

The steady-state concentrations of omadacycline and tigecycline in the plasma, epithelial lining fluid (ELF), and alveolar cells (AC) of 58 healthy adult subjects were obtained. Subjects were administered either omadacycline at 100 mg intravenously (i.v.) every 12 h for two doses followed by 100 mg i.v. every 24 h for three doses or tigecycline at an initial dose of 100 mg i.v. followed by 50 mg i.v. every 12 h for six doses. A bronchoscopy and bronchoalveolar lavage were performed once in each subject following the start of the fifth dose of omadacycline at 0.5, 1, 2, 4, 8, 12, or 24 h and after the start of the seventh dose of tigecycline at 2, 4, 6, or 12 h. The value of the area under the concentration-time curve (AUC) from time zero to 24 h postdosing (AUC_0–24) (based on mean concentrations) in ELF and the ratio of the ELF to total plasma omadacycline concentration based on AUC_0–24 values were 17.23 mg · h/liter and 1.47, respectively. The AUC_0–24 value in AC was 302.46 mg · h/liter, and the ratio of the AC to total plasma omadacycline concentration was 25.8. In comparison, the values of the AUC from time zero to 12 h postdosing (AUC_0–12) based on the mean concentrations of tigecycline in ELF and AC were 3.16 and 38.50 mg · h/liter, respectively. The ratio of the ELF and AC to total plasma concentrations of tigecycline based on AUC_0–12 values were 1.71 and 20.8, respectively. The pharmacokinetic advantages of higher and sustained concentrations of omadacycline compared to those of tigecycline in plasma, ELF, and AC suggest that omadacycline is a promising antibacterial agent for the treatment of lower respiratory tract bacterial infections caused by susceptible pathogens.

Penetration of Ciprofloxacin and Amikacin into the Alveolar Epithelial Lining Fluid of Rats with Pulmonary Fibrosis

We determined the concentration-time profiles of ciprofloxacin and amikacin in serum and alveolar epithelial lining fluid (ELF) of rats with or without pulmonary fibrosis and investigated the effect of pulmonary fibrosis on the capacity for penetration of antimicrobials into the ELF of rats. Pulmonary fibrosis was induced in rats with a single intratracheal instillation of bleomycin. After intravenous injection of ciprofloxacin or amikacin, blood and bronchoalveolar lavage fluid samples were collected. Urea concentrations in serum and lavage fluid were determined using an enzymatic assay. Ciprofloxacin and amikacin concentrations were determined by high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry, respectively. The mean ratio of ELF to plasma concentrations of ciprofloxacin at each time point in the normal group did not significantly differ from that in the pulmonary fibrosis group. However, the ratio of the ciprofloxacin area under the concentration-time curve from 0 to 24 h (AUC_0-24) in ELF to the AUC_0-24 in plasma was 1.02 in the normal group and 0.76 in the pulmonary fibrosis group. The mean ELF-to-plasma concentration ratios of amikacin at each time point in the normal group were higher than those in the pulmonary fibrosis group, reaching a statistically significant difference at 1, 2, and 4 h. The ratio of the AUC_0-24 in ELF to the AUC_0-24 in plasma was 0.49 in the normal group and 0.27 in the pulmonary fibrosis group. In conclusion, pulmonary fibrosis can influence the penetration of antimicrobials into the ELF of rats and may have a marked effect on the penetration of amikacin than that of ciprofloxacin.

Pharmacokinetic and Pharmacodynamic Principles of Anti-infective Dosing

PURPOSE

An understanding of the pharmacokinetic (PK) and pharmacodynamic (PD) principles that determine response to antimicrobial therapy can provide the clinician with better-informed dosing regimens. Factors influential on antibiotic disposition and clinical outcome are presented, with a focus on the primary site of infection. Techniques to better understand antibiotic PK and optimize PD are acknowledged.

METHODS

PubMed (inception-April 2016) was reviewed for relevant publications assessing antimicrobial exposures within different anatomic locations and clinical outcomes for various infection sites.

FINDINGS

A limited literature base indicates variable penetration of antibiotics to different target sites of infection, with drug solubility and extent of protein binding providing significant PK influences in addition to the major clearing pathway of the agent. PD indices derived from in vitro studies and animal models determine the optimal magnitude and frequency of dosing regimens for patients. PK/PD modeling and simulation has been shown an efficient means of assessing these PD endpoints against a variety of PK determinants, clarifying the unique effects of infection site and patient characteristics to inform the adequacy of a given antibiotic regimen.

IMPLICATIONS

Appreciation of the PK properties of an antibiotic and its PD measure of efficacy can maximize the utility of these life-saving drugs. Unfortunately, clinical data remain limited for a number of infection site-antibiotic exposure relationships. Modeling and simulation can bridge preclinical and patient data for the prescription of optimal antibiotic dosing regimens, consistent with the tenets of personalized medicine.

Comparison of Active Drug Concentrations in the Pulmonary Epithelial Lining Fluid and Interstitial Fluid of Calves Injected with Enrofloxacin, Florfenicol, Ceftiofur, or Tulathromycin

Bacterial pneumonia is the most common reason for parenteral antimicrobial administration to beef cattle in the United States. Yet there is little information describing the antimicrobial concentrations at the site of action. The objective of this study was to compare the active drug concentrations in the pulmonary epithelial lining fluid and interstitial fluid of four antimicrobials commonly used in cattle. After injection, plasma, interstitial fluid, and pulmonary epithelial lining fluid concentrations and protein binding were measured to determine the plasma pharmacokinetics of each drug. A cross-over design with six calves per drug was used. Following sample collection and drug analysis, pharmacokinetic calculations were performed. For enrofloxacin and metabolite ciprofloxacin, the interstitial fluid concentration was 52% and 78% of the plasma concentration, while pulmonary fluid concentrations was 24% and 40% of the plasma concentration, respectively. The pulmonary concentrations (enrofloxacin + ciprofloxacin combined) exceeded the MIC₉₀ of 0.06 μg/mL at 48 hours after administration. For florfenicol, the interstitial fluid concentration was almost 98% of the plasma concentration, and the pulmonary concentrations were over 200% of the plasma concentrations, exceeding the breakpoint (≤ 2 μg/mL), and the MIC₉₀ for Mannheimia haemolytica (1.0 μg/mL) for the duration of the study. For ceftiofur, penetration to the interstitial fluid was only 5% of the plasma concentration. Pulmonary epithelial lining fluid concentration represented 40% of the plasma concentration. Airway concentrations exceeded the MIC breakpoint for susceptible respiratory pathogens (≤ 2 μg/mL) for a short time at 48 hours after administration. The plasma and interstitial fluid concentrations of tulathromcyin were lower than the concentrations in pulmonary fluid throughout the study. The bronchial concentrations were higher than the plasma or interstitial concentrations, with over 900% penetration to the airways. Despite high diffusion into the bronchi, the tulathromycin concentrations achieved were lower than the MIC of susceptible bacteria at most time points.

Amoxicillin concentrations in relation to beta-lactamase activity in sputum during exacerbations of chronic obstructive pulmonary disease

Background

Acute exacerbations of chronic obstructive pulmonary disease (COPD) are often treated with antibiotics. Theoretically, to be maximally effective, the antibiotic concentration at sites of infection should exceed the minimum inhibitory concentration at which 90% of the growth of potential pathogens is inhibited (MIC₉₀). A previous study showed that most hospitalized COPD patients had sputum amoxicillin concentrations <LMIC₉₀ when treated with amoxicillin/clavulanic acid. Those with adequate sputum concentrations had better clinical outcomes. Low amoxicillin concentrations can be caused by beta-lactamase activity in the lungs. This study investigated whether patients with sputum amoxicillin concentrations <MIC₉₀ had higher beta-lactamase activity in sputum than patients with a concentration ≥MIC₉₀.

Methods

In total, 23 patients hospitalized for acute exacerbations of COPD and treated with amoxicillin/clavulanic acid were included. Sputum and serum samples were collected at day 3 of treatment to determine beta-lactamase activity in sputum and amoxicillin concentrations in both sputum and serum.

Results

We found no difference in beta-lactamase activity between patients with sputum amoxicillin concentrations <MIC₉₀ and ≥MIC₉₀ (P=0.79). Multivariate logistic regression analysis showed no significant relationship between beta-lactamase activity and sputum amoxicillin concentrations <MIC₉₀ or ≥MIC₉₀ (odds ratio 0.53; 95% confidence interval 0.23–1.2; P=0.13). Amoxicillin concentrations were <MIC₉₀ in 78% of sputum samples and in 30% of serum samples.

Conclusion

In patients treated with amoxicillin/clavulanic acid for an acute exacerbation of COPD, sputum beta-lactamase activity did not differ between those with sputum amoxicillin concentrations <MIC₉₀ or ≥MIC₉₀. The finding that the majority of patients had sputum amoxicillin concentrations <MIC₉₀ suggests that current treatment with antibiotics for acute exacerbations of COPD should be optimized.

Joint Intratracheal Surfactant-Antibacterial Therapy in Experimental Pseudomonas-Induced Pneumonia

BACKGROUND

The application of an exogenous pulmonary surfactant as a carrier for intratracheally administered antimicrobials represents a promising therapeutic modality that is still on its way to clinical practice. Owing to its ability to decrease surface tension, exogenous surfactant may enhance delivery of antibiotics into foci of pulmonary infection, thus increasing efficiency and safety of topical antimicrobial therapy in bacterial lung diseases.

OBJECTIVES

To assess potential interactions between exogenous surfactant and amikacin in vitro, and to study the effects of their joint intratracheal instillation in rats with acute pneumonia caused by Pseudomonas aeruginosa.

METHODS

The antibacterial and surface-active properties of amikacin (Amicil, Kievmedpreparat, Ukraine), porcine pulmonary surfactant (Suzacrin, Docpharm, Ukraine), and their combination were studied in vitro using standard microbiologic procedures and modified Pattle method (estimation of bubble diameter). Similar methods were utilized to study bacterial contamination of lungs and blood, and to assess the surface activity of bronchoalveolar wash (BAW) in 119 Wistar rats, including infected (intratracheal introduction of P. aeruginosa ATCC 27853) and noninfected animals. Histopathologic findings, differential leukocyte counts, and oxygenation parameters were recorded.

RESULTS

Antibacterial and surface-active properties of the surfactant and amikacin remained unimpaired in vitro. In rats anti-pseudomonal and anti-inflammatory effects of the surfactant-amikacin mixture were more pronounced (p<0.05) than effects of pure amikacin as evidenced by recorded rates of bacterial growth and granulocytic response. The combined therapy considerably restricted tissue damage and mitigated reduction of BAW surface activity.

CONCLUSION

The advantages of the joint surfactant-amikacin therapy of Pseudomonas-induced pneumonia may suggest further clinical trials.

Exogenous pulmonary surfactant as a vehicle for antimicrobials: assessment of surfactant-antibacterial interactions in vitro

Owing to its unique surface-active properties, an exogenous pulmonary surfactant may become a promising drug delivery agent, in particular, acting as a vehicle for antibiotics in topical treatment of pneumonia. The purpose of this study was to assess a mutual influence of natural surfactant preparation and three antibiotics (amikacin, cefepime, and colistimethate sodium) in vitro and to identify appropriate combination(s) for subsequent in vivo investigations of experimental surfactant/antibiotic mixtures. Influence of antibiotics on surface-active properties of exogenous surfactant was assessed using the modified Pattle method. Effects of exogenous surfactant on antibacterial activity of antimicrobials against Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa were evaluated using conventional microbiologic procedures. Addition of amikacin or cefepime to surfactant had no significant influence on surface-active properties of the latter. Obvious reduction of surface-active properties was confirmed for surfactant/colistimethate composition. When suspended with antibiotics, surfactant either had no impact on their antimicrobial activity (amikacin) or exerted mild to moderate influence (reduction of cefepime bactericidal activity and increase of colistimethate bacteriostatic activity against S. aureus and P. aeruginosa). Considering favorable compatibility profile, the surfactant/amikacin combination is advisable for subsequent investigation of joint surfactant/antibacterial therapy in animals with bacterial pneumonia.

Less is more: combination antibiotic therapy for the treatment of gram-negative bacteremia in pediatric patients

IMPORTANCE

Definitive combination antibiotic therapy with a β-lactam and an aminoglycoside for the treatment of gram-negative bacteremia is commonly prescribed in pediatric patients; however, its efficacy and toxicity relative to β-lactam monotherapy are unknown.

OBJECTIVE

To determine whether definitive combination antibiotic therapy affects mortality and nephrotoxicity in pediatric patients with gram-negative bacteremia.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective cohort study including pediatric patients (aged ≤18 years) with gram-negative bacteremia hospitalized at the Johns Hopkins Children's Center between 2002 and 2011.

MAIN OUTCOMES AND MEASURES

Outcomes included 30-day mortality and nephrotoxicity classified according to the pediatric RIFLE (risk for renal dysfunction, injury to the kidney, failure of kidney function, loss of kidney function, and end-stage renal disease) criteria. To account for nonrandom assignment of combination therapy, propensity score weighting was combined with multivariable logistic regression to estimate the effect of combination therapy on mortality and nephrotoxicity.

RESULTS

Of the 879 eligible pediatric patients with bacteremia, 537 (61.1%) received combination therapy. After propensity score adjustment, baseline demographic and clinical characteristics between the groups were well balanced. There was no association between combination therapy and 30-day mortality (odds ratio, 0.98; 95% CI, 0.93-1.02; P = .27). There were 170 patients (19.3%) with evidence of acute kidney injury, including 135 (25.1%) and 35 (10.2%) in the combination therapy and monotherapy arms, respectively. Patients receiving combination therapy had approximately twice the odds of nephrotoxicity compared with those receiving monotherapy (odds ratio, 2.15; 95% CI, 2.09-2.21).

CONCLUSIONS AND RELEVANCE

The use of β-lactam monotherapy for gram-negative bacteremia in pediatric patients reduces subsequent nephrotoxicity without compromising survival.

New insights in the production of aerosol antibiotics. Evaluation of the optimal aerosol production system for ampicillin-sulbactam, meropenem, ceftazidime, cefepime and piperacillin-tazobactam

BACKGROUND

Several aerosol antibiotics are on the market and several others are currently being evaluated. Aim of the study was to evaluate the aerosol droplet size of five different antibiotics for future evaluation as an aerosol administration.

MATERIALS AND METHODS

The nebulizers Sunmist(®), Maxineb(®) and Invacare(®) were used in combination with four different "small <6 ml" residual cups and two "large <10 ml" with different loadings 2-4-6-8 ml (8 ml only for large residual cups) with five different antibiotic drugs (ampicilln-sulbactam, meropenem, ceftazidime, cefepime and piperacillin-tazobactam). The Mastersizer 2000 (Malvern) was used to evaluate the produced droplet size from each combination

RESULTS

Significant effect on the droplet size produced the different antibiotic (F=96.657, p<0.001) and the residual cup design (F=68.535, p<0.001) but not the different loading amount (p=0.127) and the nebulizer (p=0.715). Interactions effects were found significant only between antibiotic and residual cup (F=16.736, p<0.001). No second order interactions were found statistically significant.

CONCLUSION

Our results firstly indicate us indirectly that the chemical formulation of the drug is the main factor affecting the produced droplet size and secondly but closely the residual cup design.

Diffusion of Oral and Intravenous 400 mg Once-Daily Moxifloxacin into Lung Tissue at Pharmacokinetic Steady-State

The degree of penetration of an antibiotic into the infection site is an important factor for its therapeutic efficacy, particularly in respiratory tract infections. In the present study, we examined the lung tissue diffusion of moxifloxacin at a dose of 400 mg administered intravenously or orally once-daily, and the results were correlated to microbiological data to estimate the clinical efficacy of moxifloxacin in lower community-acquired respiratory infections. This was a prospective, randomized, parallel-group trial, open-label, single-center study. Patients undergoing lung surgery for bronchial cancer which necessitates the removal of an anatomical piece of lung tissue were randomized into twelve treatment groups, dependent upon the time of surgery and the moxifloxacin formulation, i.v. or oral, administered. During surgery, one blood sample was taken at the time of tissue collection to determine moxifloxacin plasma concentration. At the same time, tissue samples were taken by pulmonary exeresis. A validated new high performance liquid chromatography assay was used to determine moxifloxacin concentrations in plasma and lung tissue. A total of 49 patients (25 for i.v. administration, 24 for oral administration, 44 men and 5 women, mean age, 61 years, mean body weight, 72 kg, mean creatinine clearance was 84 ml/min/1.73 m2) were enrolled. The mean +/- SD steady-state moxifloxacin ratios between lung and plasma concentrations were respectively: 3.53 +/- 1.89 and 4.36 +/- 1.48 for i.v. and oral administration. The mean steady-state moxifloxacin maximal lung concentrations (Cmax) were respectively 12.37 microg/g and 16.21 microg/g for i.v. and oral administration. Moxifloxacin both intravenously and orally exhibits high penetration in lung tissue, with tissue concentrations far above the MIC90s for most of the susceptible pathogens commonly involved, thus underlining its suitability for the treatment of community-acquired, lower respiratory tract infections.

Penetration of Ertapenem Into Different Pulmonary Compartments of Patients Undergoing Lung Surgery

Ertapenem is approved for the treatment of community-acquired pneumonia (CAP), but its in vivo penetration into lung tissue (LT), epithelial lining fluid (ELF), and alveolar cells (AC) is unknown. Fifteen patients undergoing thoracotomy were treated with 1 g intravenously for perioperative prophylaxis. Bronchoalveolar lavage was performed 1, 3, and 5 hours after ertapenem infusion. Normal LT was sampled at the time of lung extraction. Blood was collected before and at different time points up to 24 hours after infusion. Mean concentrations of ertapenem in plasma, ELF, and AC were at 1.0 hour, 63.1, 4.06, 0.004 mg/L; at 3.0 hours, 39.7, 2.59, 0.003 mg/L; and at 5.0 hours, 27.2, 2.83, 0.007 mg/L. Mean (range) concentration in LT was 7.60 (2.5-19.4) mg/kg tissue 1.5 to 4.5 hours after infusion. In plasma, ertapenem exhibited a Cmax of 94.7 +/- 23.3 mg/L and an AUC(0-last) of 501.1 +/- 266.3 mg x h/L. These results, combined with the reported (MIC)90 of most CAP bacteria, support the previously observed clinical efficacy of ertapenem in the treatment of CAP.

Intrapulmonary Pharmacokinetics of Antibacterial Agents

The idea of studying the pharmacokinetics and pharmacodynamics of antibacterials in order to predict their efficacy has long been of interest. Traditionally, serum drug concentrations have been evaluated against the minimum inhibitory concentration (MIC) of a given pathogen; however, infection site-specific data continue to gain interest from clinicians. Despite methodological limitations, progress in techniques has improved the clinical significance of data generated. Rather than using tissue homogenates which fail to differentiate between interstitial and intracellular concentrations, newer collection techniques focus on sampling of matrices that allow for this differentiation. These collection techniques now allow one to accurately describe beta-lactam and aminoglycoside interstitial penetrations, as well as, the interstitial and phagocytic concentrations of macrolides and fluoroquinolones. By using these specific data and the MICs of infecting pathogens, it is hoped that conclusions can be drawn by a clinician as to the appropriateness of the choice of an antibacterial.

Delivering Antibacterials to the Lungs

An important determinant of clinical outcome of a lower respiratory tract infection may be sterilization of the infected lung, which is also dependent on sustained antibacterial concentrations achieved in the lung. For this reason, recently there has been increased interest in measuring the concentration of antimicrobial agents at different potential sites of infection in the lung. Levels of antibacterials are now measured in bronchial mucosa, epithelial lining fluid (ELF) and alveolar macrophages, as well as in sputum. Penicillins and cephalosporins reach only marginal concentrations in bronchial secretions, whereas fluoroquinolones and macrolides have been shown to achieve high concentrations. The extent of penetration of different antibacterials into the bronchial mucosa is relatively high. This is also true for beta-lactams, although their tissue concentrations never reach blood concentrations. Antibacterials penetrate less into the ELF than into the bronchial mucosa, but fluoroquinolones appear to concentrate more into alveolar lavage than into bronchial mucosa. Pulmonary pharmacokinetics is a very useful tool for describing how drugs behave in the human lung, but it does not promote an understanding of the pharmacological effects of a drug. More important, instead, is the correlation between pulmonary disposition of the drug and its minimum inhibitory concentration (MIC) values for the infectious agent. The addition of bacteriological characteristics to in vivo pharmacokinetic studies has triggered a 'pharmacodynamic approach'. Pharmacodynamic parameters integrate the microbiological activity and pharmacokinetics of an anti-infective drug by focusing on its biological effects, particularly growth inhibition and killing of pathogens. Drugs that penetrate well and remain for long periods at the pulmonary site of infection often induce therapeutic responses greater than expected on the basis of in vitro data. However, although the determination of antibacterial concentrations at the site of infection in the lung has been suggested to be important in predicting the therapeutic efficacy of antimicrobial treatment during bacterial infections of the lower respiratory tract, some studies have demonstrated that pulmonary bacterial clearance is correlated more closely to concentrations in the serum than to those in the lung homogenates, probably because they better reflect antibacterial concentration in the interstitial fluid.

Penetration of anti-infective agents into pulmonary epithelial lining fluid: focus on antibacterial agents

The exposure-response relationship of anti-infective agents at the site of infection is currently being re-examined. Epithelial lining fluid (ELF) has been suggested as the site (compartment) of antimicrobial activity against lung infections caused by extracellular pathogens. There have been an extensive number of studies conducted during the past 20 years to determine drug penetration into ELF and to compare plasma and ELF concentrations of anti-infective agents. The majority of these studies estimated ELF drug concentrations by the method of urea dilution and involved either healthy adult subjects or patients undergoing diagnostic bronchoscopy. Antibacterial agents such as macrolides, ketolides, newer fluoroquinolones and oxazolidinones have ELF to plasma concentration ratios of >1. In comparison, β-lactams, aminoglycosides and glycopeptides have ELF to plasma concentration ratios of ≤1. Potential explanations (e.g. drug transporters, overestimation of the ELF volume, lysis of cells) for why these differences in ELF penetration occur among antibacterial classes need further investigation. The relationship between ELF concentrations and clinical outcomes has been under-studied. In vitro pharmacodynamic models, using simulated ELF and plasma concentrations, have been used to examine the eradication rates of resistant and susceptible pathogens and to explain why selected anti-infective agents (e.g. those with ELF to plasma concentration ratios of >1) are less likely to be associated with clinical treatment failures. Population pharmacokinetic modelling and Monte Carlo simulations have recently been used and permit ELF and plasma concentrations to be evaluated with regard to achievement of target attainment rates. These mathematical modelling techniques have also allowed further examination of drug doses and differences in the time courses of ELF and plasma concentrations as potential explanations for clinical and microbiological effects seen in clinical trials. Further studies are warranted in patients with lower respiratory tract infections to confirm and explore the relationships between ELF concentrations, clinical and microbiological outcomes, and pharmacodynamic parameters.

Zanamivir pharmacokinetics and pulmonary penetration into epithelial lining fluid following intravenous or oral inhaled administration to healthy adult subjects

Zanamivir serum and pulmonary pharmacokinetics were characterized following intravenous (i.v.) or oral inhaled administration. I.v. zanamivir was given as intermittent doses of 100 mg, 200 mg, and 600 mg every 12 h (q12h) for two doses or as a continuous infusion (6-mg loading dose followed by 3 mg/h for 12 h). Oral inhaled zanamivir (two 5-mg inhalations q12h for two doses) was evaluated as well. Each zanamivir regimen was administered to six healthy subjects with serial pharmacokinetic sampling. In addition, a single bronchoalveolar lavage (BAL) fluid sample was collected at various time points and used to calculate epithelial lining fluid (ELF) drug concentrations for each subject. For intermittent i.v. administration of 100 mg, 200 mg, and 600 mg zanamivir, the median zanamivir concentrations in ELF collected 12 h after dosing were 74, 146, and 419 ng/ml, respectively, each higher than the historic mean 50% inhibitory concentrations for the neuraminidases of wild-type strains of influenza A and B viruses. Median ELF/serum zanamivir concentration ratios ranged from 55 to 79% for intermittent i.v. administration (when sampled 12 h after the last dose) and 43 to 45% for continuous infusion (when sampled 6 to 12 h after the start of the infusion). For oral inhaled zanamivir, the median zanamivir concentrations in ELF were 891 ng/ml for the first BAL fluid collection and 326 ng/ml for subsequent BAL fluid collections (when sampled 12 h after the last dose); corresponding serum drug concentrations were undetectable. This study demonstrates zanamivir's penetration into the human pulmonary compartment and supports the doses selected for the continuing development of i.v. zanamivir in clinical studies of influenza.

Relation between amoxicillin concentration in sputum of COPD patients and length of hospitalization

Amoxicillin is a widely used antibiotic in COPD. Little is known about the transfer of amoxicillin into sputum of COPD patients. The objective was to investigate the relationship between the concentration of amoxicillin in sputum in hospitalized COPD patients and length of hospitalization. To be effective against bacterial pathogens, the amoxicillin concentration in target tissues should be higher than the Minimal Inhibiting Concentration (MIC) of 2 mg/l. Therefore, this was also used as the cut-off value for the amoxicillin concentration in sputum, as a marker for lung tissue concentration. Fifty-two COPD in-patients with an exacerbation, treated with amoxicillin clavulanic acid, were included in this cohort study. Of these patients 7 also had pneumonia. Patients were divided in patients with an amoxicillin sputum concentration ≥ 2 mg/l and < 2 mg/l. Furthermore, inflammation markers in sputum and serum and clinical parameters were obtained. Of the 33 patients with usable sputum, 11 had a concentration in sputum ≥ 2 mg/l. The mean length of hospitalization for patients with concentrations below the MIC90 to common respiratory pathogens was 11.0 days, while for patients with concentrations at or above the MIC90 this was 7.0 days (p = 0.005). COPD patients admitted for an acute exacerbation of COPD, with a sputum concentration of amoxicillin ≥ 2 mg/l had a markedly reduced length of hospitalization compared to patients with a concentration < 2 mg/l. It is worthwhile testing whether individualized treatment based on sputum amoxicillin concentrations of patients during hospitalization for acute exacerbations can effectively reduce hospital stay.

Clinical practice guidelines for hospital-acquired pneumonia and ventilator-associated pneumonia in adults

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are important causes of morbidity and mortality, with mortality rates approaching 62%. HAP and VAP are the second most common cause of nosocomial infection overall, but are the most common cause documented in the intensive care unit setting. In addition, HAP and VAP produce the highest mortality associated with nosocomial infection. As a result, evidence-based guidelines were prepared detailing the epidemiology, microbial etiology, risk factors and clinical manifestations of HAP and VAP. Furthermore, an approach based on the available data, expert opinion and current practice for the provision of care within the Canadian health care system was used to determine risk stratification schemas to enable appropriate diagnosis, antimicrobial management and nonantimicrobial management of HAP and VAP. Finally, prevention and risk-reduction strategies to reduce the risk of acquiring these infections were collated. Future initiatives to enhance more rapid diagnosis and to effect better treatment for resistant pathogens are necessary to reduce morbidity and improve survival.

Disposition of gamithromycin in plasma, pulmonary epithelial lining fluid, bronchoalveolar cells, and lung tissue in cattle

OBJECTIVE

To determine the disposition of gamithromycin in plasma, pulmonary epithelial lining fluid (PELF), bronchoalveolar lavage (BAL) cells, and lung tissue homogenate in cattle.

ANIMALS

33 healthy Angus calves approximately 7 to 8 months of age.

PROCEDURES

Calves were randomly assigned to 1 of 11 groups consisting of 3 calves each, which differed with respect to sample collection times. In 10 groups, 1 dose of gamithromycin (6 mg/kg) was administered SC in the neck of each calf (0 hours). The remaining 3 calves were not treated. Gamithromycin concentrations in plasma, PELF, lung tissue homogenate, and BAL cells (matrix) were measured at various points by means of high-performance liquid chromatography with tandem mass spectrometry.

RESULTS

Time to maximum gamithromycin concentration was achieved at 1 hour for plasma, 12 hours for lung tissue, and 24 hours for PELF and BAL cells. Maximum gamithromycin concentration was 27.8 μg/g, 17.8 μg/mL, 4.61 μg/mL, and 0.433 μg/mL in lung tissue, BAL cells, PELF, and plasma, respectively. Terminal half-life was longer in BAL cells (125.0 hours) than in lung tissue (93.0 hours), plasma (62.0 hours), and PELF (50.6 hours). The ratio of matrix to plasma concentrations ranged between 4.7 and 127 for PELF, 16 and 650 for lung tissue, and 3.2 and 2,135 for BAL cells.

CONCLUSIONS AND CLINICAL RELEVANCE

Gamithromycin was rapidly absorbed after SC administration. Potentially therapeutic concentrations were achieved in PELF, BAL cells, and lung tissue within 30 minutes after administration and persisted for 7 (PELF) to > 15 (BAL cells and lung tissue) days after administration of a single dose.

Potential role of tigecycline in the treatment of community-acquired bacterial pneumonia

Tigecycline is a member of the glycylcycline class of antimicrobials, which is structurally similar to the tetracycline class. It demonstrates potent in vitro activity against causative pathogens that are most frequently isolated in patients with community-acquired bacterial pneumonia (CABP), including (but not limited to) Streptococcus pneumoniae (both penicillin-sensitive and -resistant strains), Haemophilus influenzae and Moraxella catarrhalis (including β-lactamase-producing strains), Klebsiella pneumoniae, and ‘atypical organisms’ (namely Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila). Comparative randomized clinical trials to date performed in hospitalized patients receiving tigecycline 100 mg intravenous (IV) × 1 and then 50 mg IV twice daily thereafter have demonstrated efficacy and safety comparable to the comparator agent. Major adverse effects were primarily gastrointestinal in nature. Tigecycline represents a parenteral monotherapy option in hospitalized patients with CABP (especially in patients unable to receive respiratory fluoroquinolones). However, alternate and/or additional therapies should be considered in patients with more severe forms of CABP in light of recent data of increased mortality in patients receiving tigecycline for other types of severe infection.

Antimicrobial chemotherapy and lung microdialysis: a review

Pneumonia is a form of lung infection that may be caused by various micro-organisms. The predominant site of infection in pneumonia is debatable. Advances in the fields of diagnostic and therapeutic medicine have had a less than optimal effect on the outcome of pneumonia and one of the many causes is likely to be inadequate antimicrobial concentrations at the site of infection in lung tissue. Traditional antimicrobial therapy guidelines are based on indirect modelling from blood antimicrobial levels. However, studies both in humans and animals have shown the fallacy of this concept in various tissues. Many different methods have been employed to study lung tissue antimicrobial levels with limited success, and each has limitations that diminish their utility. An emerging technique being used to study the pharmacokinetics of antimicrobial agents in lung tissue is microdialysis. Development of microdialysis catheters, along with improvement in analytical techniques, has improved the accuracy of the data. Unfortunately, very few studies have reported the use of microdialysis in lung tissue, and even fewer antimicrobial classes have been studied. These studies generally suggest that this technique is a safe and effective way of assessing the pharmacokinetics of antimicrobial agents in lung tissue. Further descriptive studies need to be conducted to study the pharmacokinetics and pharmacodynamics of different antimicrobial classes in lung tissue. Data emanating from these studies could inform decisions for appropriate dosing schedules of antimicrobial agents in pneumonia.

Management of aminoglycosides in the intensive care unit

Antibacterial resistance is increasing throughout the world, while the development of new agents is slowly progressing. In addition, the increasing prevalence of fluoroquinolone resistance may force many practitioners to choose an aminoglycoside agent in gram-negative regimens. Aminoglycosides are bactericidal agents with potent activity against gram-negative infections and activity against gram-positive infections when added to a cell wall active antimicrobial-based regimen. These agents may be dosed multiple times a day or consolidated as high-dose, extended-interval dosing to maximize pharmacokinetic and pharmacodynamic properties to achieve possible improved efficacy with reduced toxicity. Clinical application includes the treatment of bacteremia, endocarditis, health-care and nosocomial pneumonias, intra-abdominal infections, and others. Nephrotoxicity and ototoxicity are potential risks of aminoglycoside therapy that may be minimized with serum monitoring and short courses of therapy.

The importance of tissue penetration in achieving successful antimicrobial treatment of nosocomial pneumonia and complicated skin and soft-tissue infections caused by methicillin-resistant Staphylococcus aureus: vancomycin and linezolid

BACKGROUND

The rising prevalence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) and the recent emergence of community-associated MRSA are major clinical, public health, and economic challenges. MRSA is a leading cause of nosocomial pneumonia and complicated skin and soft-tissue infections (cSSTI). Vancomycin and linezolid are two commonly used antimicrobial agents with activity against Gram-positive pathogens, particularly MRSA, that are used to treat both nosocomial pneumonia and cSSTI. Recently, the therapeutic efficacy of vancomycin in the treatment of hospitalized patients with MRSA infections has been questioned due to the emergence of MRSA strains with reduced susceptibility to vancomycin together with concerns related to inadequate dosing and poor tissue penetration of the drug.

SCOPE

A literature review was conducted to investigate the pharmacokinetics and pulmonary and tissue penetration of vancomycin and linezolid. Using MEDLINE and EMBASE, the most relevant articles in English published over the past 25 years (up to October 2008) were identified and summarized. Studies in human volunteers and adult patients that measured concentrations of antibiotic in serum, epithelial lining fluid (ELF), and tissue were selected for further review.

FINDINGS

For both drugs, pharmacokinetic studies were conducted in diverse patient populations and employed varying techniques to measure tissue concentrations. Vancomycin concentrations in ELF ranged from 5 to 25% of simultaneous plasma levels, while concentrations in whole homogenized lung tissue were slightly higher (24-41%). Distribution of vancomycin into soft tissue was variable. For linezolid, overall mean concentrations in ELF and in soft tissue were generally similar or higher than simultaneous plasma levels, although variability in tissue penetration across studies in healthy volunteers and patients was seen.

LIMITATIONS

The studies included in this review vary greatly in their designs and patient populations; this, together with methodologic difficulties, limits the interpretation of the data.

CONCLUSIONS

In the absence of clinical data correlating ELF concentrations and clinical outcome, the clinical significance of differences in pulmonary penetration of vancomycin and linezolid is unknown. Higher vancomycin serum concentrations may be necessary to achieve appropriate lung concentrations to optimize treatment outcomes. Linezolid demonstrates adequate penetration into lung and other soft issues with sustained concentrations above the minimum inhibitory concentrations for susceptible pathogens, including MRSA, for the majority of the dosing interval. Examination of the pharmacokinetic data adds insights not provided by the clinical trial data and together provides clinicians with a more comprehensive basis for selecting appropriate antimicrobial therapy for the treatment of serious MRSA infections.

Comparison of the pharmacodynamics of biapenem in bronchial epithelial lining fluid in healthy volunteers given half-hour and three-hour intravenous infusions

The time above the MIC (T>MIC) is the pharmacokinetic/pharmacodynamic (PK/PD) parameter that correlates with the therapeutic efficacy of beta-lactam antibiotics. A prolonged infusion can provide plasma drug concentrations that remain above the MIC for a long period. The objective of this study was to compare the PK/PD parameters in bronchial epithelial lining fluid (ELF) of biapenem given as 0.5-h and 3-h infusions by using bronchoscopic microsampling (BMS). Six healthy adult volunteers received 0.5-h and 3-h infusions of 0.3 g of biapenem with a washout interval. BMS was performed repeatedly from 0.5 to 24 h after biapenem administration in order to determine the pharmacokinetics in bronchial ELF. The subjects received intravenous biapenem with the same regimens again and then underwent bronchoalveolar lavage (BAL) at the end of infusion in order to determine the concentration of the drug in alveolar ELF. The percentages (means +/- standard deviations) of T>MIC in bronchial ELF at MICs from 0.25 to 4 microg/ml ranged from zero to 34.6% +/- 5.2% after the 0.5-h infusion and from 5.1% +/- 5.6% to 52.2% +/- 17.0% after the 3-h infusion. The percentage of T>MIC in bronchial ELF after the 3-h infusion tended to be higher than that after the 0.5-h infusion. The concentrations of the drug in alveolar ELF after 0.5-h and 3-h infusions were 3.5 +/- 1.2 microg/ml and 1.3 +/- 0.3 microg/ml, respectively. The present results support the use of prolonged infusions of beta-lactam antibiotics and may provide critical information for successful treatment of lower respiratory tract infections based on PK/PD parameters in bronchial ELF.

Sputum antibiotic concentrations: implications for treatment of cystic fibrosis lung infection

BACKGROUND

The success of antibiotic therapy may be predicted based on the achievement of pharmacodynamic indices (PDIs), which are determined by the susceptibility of the infecting bacteria and the concentrations of antibiotics achieved at the site of infection. The aim of this study was to determine whether PDIs associated with clinical effectiveness for ceftazidime and tobramycin were achieved at the site of infection in the lungs of cystic fibrosis (CF) patients following intravenous administration during treatment of an acute exacerbation.

METHODS

Serum and sputum samples were collected from 14 CF patients and the concentration of both antibiotics in the samples determined. The susceptibility of bacteria cultured from sputum samples to both antibiotics alone and in combination was also determined.

RESULTS

A total of 22 Pseudomonas aeruginosa isolates and 4 Burkholderia cepacia complex isolates were cultured from sputum samples with 55% and 4% of isolates susceptible to ceftazidime and tobramycin, respectively. Target PDIs for ceftazidime and tobramycin, an AUC/MIC ratio of 100 and a C(max)/MIC ratio of 10, respectively, were not achieved in serum or sputum simultaneously or even individually for any patient. Although the combination of ceftazidime and tobramycin was synergistic against 20 of the 26 isolates cultured, the concentrations of both antibiotics required for synergy were achieved simultaneously in only 38% of serum and 14% of sputum samples.

CONCLUSION

Key PDIs associated with clinical effectiveness for ceftazidime and tobramycin were not achieved at the site of infection in the lungs of CF patients.

Intrapulmonary distribution of intravenous telavancin in healthy subjects and effect of pulmonary surfactant on in vitro activities of telavancin and other antibiotics

Steady-state concentrations of telavancin, a novel, bactericidal lipoglycopeptide, were determined in the plasma, pulmonary epithelial lining fluid (ELF), and alveolar macrophages (AMs) of 20 healthy subjects. Telavancin at 10 mg of drug/kg of body weight/day was administered as a 1-h intravenous infusion on three successive days, with bronchoalveolar lavage performed on five subjects, each at 4, 8, 12, and 24 h after the last dose. Plasma samples were collected before the first and third infusions and at 1, 2, 3, 4, 8, 12, and 24 h after the third infusion. The plasma telavancin concentration-time profile was as reported previously. Telavancin (mean +/- standard deviation) penetrated well into ELF (3.73 +/- 1.28 microg/ml at 8 h and 0.89 +/- 1.03 microg/ml at 24 h) and extensively into AMs (19.0 +/- 16.8 microg/ml at 8 h, 45.0 +/- 22.4 microg/ml at 12 h, and 42.0 +/- 31.4 microg/ml at 24 h). Mean concentrations in AMs and plasma at 12 h were 45.0 microg/ml and 22.9 microg/ml (mean AM/plasma ratio, 1.93), respectively, and at 24 h were 42.0 microg/ml and 7.28 microg/ml (mean AM/plasma ratio, 6.67), respectively. Over the entire dosing interval, telavancin was present in ELF and AMs at concentrations up to 8-fold and 85-fold, respectively, above its MIC 90 for methicillin-resistant Staphylococcus aureus (0.5 microg/ml). Pulmonary surfactant did not affect telavancin's in vitro antibacterial activity. Telavancin was well tolerated. These results support the proposal for further clinical evaluation of telavancin for treating gram-positive respiratory infections.

A pilot study testing whether concentrations of levofloxacin in interstitial space fluid of soft tissues may serve as a surrogate for predicting its pharmacokinetics in lung

Recent observations indicate that pharmacokinetics of beta-lactam antibiotics in the lung can be predicted by the use of concentration versus time profiles in peripheral soft tissues. If this observation is transferred to other classes of antimicrobials, measurement of antimicrobial concentrations in peripheral tissues would enable prediction of the pharmacokinetics of antimicrobials at the site of the respiratory tract infection. We set out to test the hypothesis that concentrations of the fluoroquinolone levofloxacin in the respiratory tract can be predicted on the basis of knowledge of its pharmacokinetics in peripheral soft tissues. After administration of a single intravenous dose of 500mg of levofloxacin, microdialysis was used to describe the concentration versus time profiles of levofloxacin in the interstitial space fluid of lung tissue of patients (n=5) undergoing elective lung surgery. These data were compared with the concentration versus time courses in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue of healthy volunteers (n=7). The median AUC(0-infinity) of free levofloxacin in lung (2267mg x min/L, 1980-2355) was about 2-fold and 1.5-fold lower compared with skeletal muscle (4381mg x min/L, range 1720-8195) and adipose tissue (3492mg x min/L, range 1323-6420) of healthy controls, respectively. Concentrations in the interstitial space fluid of the lung were descriptively lower compared with corresponding concentrations in peripheral soft tissues. This is in contrast to previous observations made for the class of beta-lactam antibiotics, and indicates that pharmacokinetics of levofloxacin derived from soft tissues may not be used uncritically for prediction of levofloxacin concentrations in the interstitium of the lung.

Pharmacokinetics of telithromycin using bronchoscopic microsampling after single and multiple oral doses

OBJECTIVES

Bronchoscopic microsampling (BMS) is a new technique for repeated sampling of bronchial epithelial lining fluid (ELF) to obtain the pharmacokinetic profile of drugs. We analyzed the time versus concentration profiles of telithromycin in bronchial ELF obtained by BMS and compared these finding to those in plasma and alveolar ELF obtained by bronchoalveolar lavage (BAL).

METHODS

Bronchial ELF samples were obtained from five healthy subjects using BMS probe at 0, 2, 3, 4, 6, 10 and 24h after single or multiple oral doses of 600 mg of telithromycin. Alveolar ELF was also obtained by BAL 3h after single or multiple oral doses of 600 mg of telithromycin.

RESULTS

The areas under the concentration-time curve from 0 to 24h (AUC0-24) of telithromycin in plasma and bronchial ELF were 2.86+/-0.60 and 19.5+/-10.4 mg h/l after single treatment and 3.60+/-0.49 and 42.2+/-22.7 mg h/l after multiple treatments, respectively. Single and multiple oral doses of telithromycin produced significantly (p<0.05) higher AUC0-24 in bronchial ELF compared to those in plasma. While concentrations in bronchial ELF obtained by BMS were significantly lower than those in alveolar ELF obtained by BAL, they tended to be higher than those in plasma after multiple administration. The telithromycin concentrations obtained by BMS method were very consistent in bronchial ELF at different bronchi at one time point and at the same bronchus at different time points.

CONCLUSIONS

Using the BMS technique, we could describe the pharmacokinetics of telithromycin in bronchial ELF. Furthermore, BMS was reasonably validated and reconfirmed to be a feasible and reliable method for measuring antimicrobial concentrations in bronchial ELF.

Potential Impact of Vancomycin Pulmonary Distribution on Treatment Outcomes in Patients with Methicillin-ResistantStaphylococcus aureusPneumonia

Vancomycin as the drug of choice for treatment of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia has been called into question on the basis of therapeutic failures. In patients with MRSA pneumonia, treatment failures are probably due to the complex interplay of variables affecting the host-antimicrobial-pathogen interrelationship. However, it has been suggested that decreased penetration of vancomycin into the lungs may contribute. This review explores physiochemical and physiologic variables that affect pulmonary penetration and describes methods used in quantifying pulmonary vancomycin concentrations. Most important, findings are evaluated in the clinical context of the chemotherapeutic options available for treatment of MRSA pneumonia. The possibility of increased serum vancomycin concentrations as a method to optimize current treatment outcomes is also explored.

Lung microdialysis--a powerful tool for the determination of exogenous and endogenous compounds in the lower respiratory tract (mini-review)

In vivo measurement of concentrations of drugs and endogenous substances at the site of action has become a primary focus of research. In this context the minimal invasive microdialysis (MD) technique has been increasingly employed for the determination of pharmacokinetics in lung. Although lung MD is frequently employed to investigate various drugs and endogenous substances, the majority of lung MD studies were performed to determine the pharmacokinetic profile of antimicrobials that can be related to the importance of respiratory tract infections. For the lower respiratory tract various methods, such as surgical collection of whole lung tissue and bonchoalveolar lavage (BAL), are currently available for the determination of pharmacokinetics of antimicrobials. Head-to-head comparison of pharmacokinetics of antibiotics in lung revealed high differences between MD and conventional methods. MD might be regarded as a more advantageous approach because of its higher anatomical resolution and the ability to obtain dynamic time-vs-concentration profiles within one subject. However, due to ethical objections lung MD is limited to animals or patients undergoing elective thoracic surgery. From these studies it was speculated that the concentrations in healthy lung tissue may be predicted reasonably by the measurement of concentrations in skeletal muscle tissue. However, until now this was only demonstrated for beta-lactam antibiotics and needs to be confirmed for other classes of antimicrobials. In conclusion, the present review shows that MD is a promising method for the determination of antimicrobials in the lung, but might also be applicable for measuring a wide range of other drugs and for the investigation of metabolism in the lower respiratory tract.

Penetration of gentamicin into the alveolar lining fluid of critically ill patients with ventilator-associated pneumonia

STUDY OBJECTIVES

To estimate the penetration of gentamicin into lung tissue by measuring its concentrations in alveolar lining fluid (ALF) and blood in critically ill patients with ventilator-associated pneumonia (VAP).

PATIENTS AND INTERVENTIONS

The study population consisted of 24 patients who were admitted to an ICU for respiratory failure and developed VAP. Patients were scheduled to undergo bronchoscopy with BAL after IV administration of a once-daily, 240-mg schedule of gentamicin for the treatment of VAP. Patients were assigned at random to one of four groups of six patients each according to the scheduled time for bronchoscopy (1, 2, 4, or 6 h, respectively). A serum sample was obtained at 0.5 h (n = 24), and both serum and ALF samples (n = 6) were collected at each of the above specified times for measurement of antibiotic concentrations.

MEASUREMENTS AND RESULTS

Mean +/- SEM gentamicin concentrations in the ALF were 2.95 +/- 0.37, 4.24 +/- 0.42, 3.10 +/- 0.39, and 2.65 +/- 0.35 microg/mL at 1, 2, 4, and 6 h, respectively, after the start of antibiotic infusion. Maximum gentamicin concentrations in serum (13.39 +/- 0.91 mug/mL, n = 24) and ALF (4.24 +/- 0.42 microg/mL, n = 6) were achieved at 0.5 h and 2 h, respectively, giving a penetration ratio of 0.32. The mean ratios of ALF/serum concentrations between 1 h and 6 h ranged from 0.30 to 1.14. After completion of the distribution phase, a significant positive correlation (p = 0.02) was found between gentamicin concentrations in the serum and ALF.

CONCLUSIONS

Once-daily IV administration of 240-mg gentamicin achieved average peak antibiotic concentrations of 4.24 microg/mL in the ALF 2 h after administration, and an ALF/serum penetration ratio of 32%. Higher gentamicin doses to produce higher peak blood levels than those found with the study dose are necessary to obtain active alveolar concentrations against less sensitive microorganisms in the treatment of VAP in ICU patients.

Antimicrobial Treatment of Hospital-Acquired Pneumonia

This article highlights the importance of providing adequate empirical antibiotic therapy for hospital-acquired pneumonia and avoiding the excessive use of antibiotics. To meet these goals, a strategy for the management of suspected ventilator-associated pneumonia should include obtaining reliable pulmonary specimens for direct microscope examination and cultures before new antibiotics are administered.

Recent Trends in the Management of Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) occurs frequently in mechanically ventilated patients and has a high mortality rate. To date, there is no consensus for the diagnosis of VAP. Effective reduction in VAP-inducedmortality requires amultifaceted approach to include assessment of individual risks for VAP, implementation of effective ventilator handling procedures, routine use of VAP prevention strategies, appropriate use and interpretation of invasive and noninvasive diagnostic tests, and early broad spectrum antibiotic coverage with narrowing of coverage and cessation of therapy based on clinical improvement. Pharmacokinetic and pharmacodynamic principlesmust be used in designingempiric antibiotic regimens. Because an inappropriate empiric regimen in VAP has been associated with increasedmortality, it is imperative to maintain intensive care unit–specific epidemiologic data.