Comments
Abstract
Rationale: Pneumonia is a frequent and feared complication in intubated critically ill patients. Tissue concentrations of antimicrobial drugs need to be sufficiently high to treat the infection and also prevent development of bacterial resistance. It is uncertain whether pulmonary inflammation and injury affect antimicrobial drug penetration into lung tissue.
Objectives: To determine and compare tissue and BAL fluid concentrations of ceftaroline fosamil and linezolid in a model of unilateral acute lung injury in pigs and to evaluate whether dose adjustment is necessary to reach sufficient antimicrobial concentrations in injured lung tissue.
Methods: After induction of unilateral acute lung injury, ceftaroline fosamil and linezolid were administered intravenously. Drug concentrations were measured in lung tissue through microdialysis and in blood and BAL fluid samples during the following 8 hours. The primary endpoint was the tissue concentration area under the concentration curve in the first 8 hours (AUC0–8 h) of the two antimicrobial drugs.
Measurements and Main Results: In 10 pigs, antimicrobial drug concentrations were higher in inflamed and injured lung tissue compared with those in uninflamed and uninjured lung tissue (median ceftaroline fosamil AUC0–8 h [and interquartile range] = 26.7 mg ⋅ h ⋅ L−1 [19.7–39.0] vs. 16.0 mg ⋅ h ⋅ L−1 [13.6–19.9], P = 0.02; median linezolid AUC0–8 h 76.0 mg ⋅ h ⋅ L−1 [68.1–96.0] vs. 54.6 mg ⋅ h ⋅ L−1 [42.7–60.9], P = 0.01), resulting in a longer time above the minimal inhibitory concentration and in higher peak concentrations and dialysate/plasma ratios. Penetration into BAL fluid was excellent for both antimicrobials, but without left-to-right differences (ceftaroline fosamil, P = 0.78; linezolid, P = 1.00).
Conclusions: Tissue penetration of two commonly used antimicrobial drugs for pneumonia is enhanced by early lung tissue inflammation and injury, resulting in longer times above the minimal inhibitory concentration. Thus, lung tissue inflammation ameliorates antimicrobial drug penetration during the acute phase.
Antimicrobial therapy fails in a substantial number of critically ill patients suffering from acute respiratory distress syndrome in the ICU. Tissue concentrations of antimicrobial drugs need to be sufficiently high to treat the infection and also prevent development of bacterial resistance. It is uncertain whether pulmonary inflammation and injury affect antimicrobial drug penetration into lung tissue.
Tissue penetration of linezolid and ceftaroline fosamil, two commonly used antimicrobial drugs for treatment of pneumonia, is enhanced by early lung tissue inflammation and injury, resulting in longer times above the minimal inhibitory concentration. Thus, lung tissue inflammation ameliorates antimicrobial drug penetration of the examined antimicrobial substances during the acute phase of lung injury.
Acute respiratory distress syndrome (ARDS) is a life-threatening condition characterized by pulmonary inflammation, diffuse alveolar damage, increased alveolar capillary permeability, and pulmonary edema (1, 2). Patients with ARDS often receive invasive ventilation, which increases the risk of pulmonary infection (3). If pneumonia develops, which is one of the most common infections in the ICU (4), both timely administration of appropriate antimicrobial drugs (5–7) and sufficiently high antimicrobial drug concentrations in lung tissue are essential (8).
Ceftaroline fosamil and linezolid are effective antimicrobial drugs against pneumonia caused by Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus, in critically ill patients (6, 7, 9–11). Nevertheless, mortality remains high in hospital-acquired pneumonia, especially associated with mechanical ventilation (ventilator-associated pneumonia) (12, 13). This is surprising, as intravenous administration of both drugs result in high concentrations in BAL (14, 15). Whether BAL concentrations reflect concentrations in lung tissue, especially when this tissue is inflamed and injured, can be questioned (14).
We hypothesized that local concentrations of ceftaroline fosamil and linezolid are dependent on local inflammation and injury. To test this hypothesis, we measured and compared interstitial lung tissue concentrations through microdialysis in inflamed and injured tissue with uninflamed and uninjured tissue in an established model of unilateral acute lung injury (ALI) in pigs (16). We also compared tissue concentrations in BAL fluid (BALF) and in plasma. The model allows us to directly compare tissue concentrations of antimicrobial drugs in inflamed and injured lung lobes with uninflamed and uninjured lung lobes within each single animal.
Some of the results of these studies have been previously reported in the form of a poster presentation at the European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) 2023 (17).
The animal experiment was approved by the Ethics Committee for Animal Research of the Medical University of Vienna, Vienna, Austria (21/115–97/98). Before the experiment, animals were kept in groups on dry straw beds and fed as appropriate for their species. Twelve Austrian Landrace pigs (Sus scrofa domesticus) with a mean body weight of 60.9 ± 7.2 kg were used; two pigs (16.7%) died early in the experiments, the data of which were not included in the final analysis. At the end of the experiment, pigs were killed with an overdose of fentanyl and intravenous infusion of potassium chloride.
Experiment details, including the timing of drug administration and sampling, are presented in Figure 1 and explained elsewhere (see the online supplement). In short, after the induction of anesthesia, intubation, and the start of invasive ventilation, a median sternotomy was performed for placement of six microdialysis probes into each animal, three on each side (upper lobe, midzone area, and lower lobe, respectively). Then, left unilateral ALI was induced as described previously (16). Subsequently, ceftaroline fosamil and linezolid were administered intravenously, and sampling of blood, lung tissue dialysate, and BALF was performed for intermittent measurement of the concentrations of these antimicrobial agents.
Figure 1. Overview of timeline, interventions and sampling periods. Time point 0 marks the beginning of the measurements and application of antibiotics after induction of unilateral ALI. One animal died after 1 hour, and one died after 3 hours. ALI = acute lung injury; Cdyn = dynamic compliance; CEF = ceftaroline fosamil; DLTm = modified double-lumen tube; LIN = linezolid; MD = microdialysis.
[More] [Minimize]The details of this established model of unilateral ALI have been reported previously (16). The left lung was cyclically rinsed with 0.9% saline + 0.3% TritonX-100 (Sigma– Aldrich) with the pig in the lateral decubitus position using a bronchoscopically confirmed correctly placed modified double-lumen endotracheal tube. Thereafter, the pig was repositioned in the supine position for the rest of the experiment. The presence of lung injury was confirmed by a drop of dynamic compliance below 50% of baseline in the left lung (16).
One dose of 600 mg ceftaroline fosamil (Zinforo, Pfizer GmbH) and one dose of 600 mg linezolid (Zyvoxid, Pfizer GmbH) was administered intravenously over a period of 60 minutes; a second dose of 600 mg ceftaroline fosamil was administered 6 hours later. Ceftaroline fosamil at 600 mg every 12 hours is the dosing interval that is approved by the Food and Drug Administration, but typically higher doses are used in suspected methicillin-resistant Staphylococcus aureus infections, usually 600 mg every 8 hours (18). We deliberately chose 600 mg every 6 hours to evaluate pharmacokinetics in tissue (injured vs. uninjured) associated with a repeated bolus administration. For all adult patients, linezolid at 600 mg every 12 hours is a well-established dosing regimen that we have chosen, even though recent data suggest that certain subpopulations in ICU patients may require higher doses of linezolid to meet pharmacokinetic and pharmacodynamic targets for efficacy (19).
Blood samples were drawn at fixed time intervals as follows: from 0 to 2 hours every 20 minutes; from 2 to 6 hours every 30 minutes, and from 6 to 8 hours every 20 minutes. Samples were immediately placed on ice, centrifuged at 2,000 × g at 4°C for 10 minutes, and shock frozen at −80°C within 3 to 5 minutes.
Microdialysis probe dialysate was collected in vials at the same time points as when blood was sampled. Dialysate was immediately stored at −80°C within 3 to 5 minutes. At the end of the experiment, retrodialysis was performed for probe calibration as described previously (20). Relative recovery (RR) and true extracellular concentration of unbound antibiotic concentration was calculated as follows: RR (%) = 100 − 100 × ([analyte]dialysate/ [analyte]perfusate), and tissue concentration = 100 × ([MD sample]/RR%), wherein [analyte]dialysate is the concentration of the retrodialysis samples and [analyte]perfusate is the concentration used in the perfusion solution (20).
BAL was performed at 1, 2, 4, and 7 hours from both lungs separately; first, the left lung and thereafter, the right lung. BALF was immediately placed on ice, centrifuged at 2,000 × g at 4°C for 10 min, and shock frozen at −80°C within 3 to 5 minutes.
After the experiment, six histological specimens were taken from each animal, from the insertion site of the six microdialysis probes, and were stored until histological examination. A total of 24 specimens were analyzed, comprising six specimens from four randomly selected pigs. These 24 specimens included 12 specimens of injured and inflamed lung tissue and 12 specimens of uninjured and uninflamed lung tissue, respectively. These specimens were appropriately fixed, sized, placed in tissue capsules, subjected to overnight drainage, and ultimately embedded in paraffin. Twenty high power fields of each single specimen were analyzed by a pathologist, and a detailed description of the preparation and staining of the specimens can be found in the online supplement.
We measured concentrations of ceftaroline fosamil and linezolid in microdialysate and BALF using high-performance liquid chromatography as described previously and detailed in the online supplement. Blood urea nitrogen (BUN) was measured in serum (BUNSER) and BALF (BUNBALF) with a urea assay kit (Abnova). Concentrations of ceftaroline fosamil and linezolid in epithelial lining fluid (ELF; ceftaroline fosamilELF, and linezolidELF, respectively) were calculated using the drug concentrations in BALF (drugBALF) and BUNSER and BUNBALF as described previously (14, 21, 22): drugELF = drugBALF × BUNSER/BUNBALF.
The primary endpoints of this were the overall antimicrobial drug concentrations in lung tissue (AUC0–8 h). Secondary endpoints included various pharmacodynamic parameters and penetration ratios into lung tissue and BALF as listed in Table 1.
| Measurement | Median (IQR) for: | |||
|---|---|---|---|---|
| Ceftaroline Fosamil | Linezolid | |||
| Left Inflamed and Injured Lung | Right Inflamed and Uninjured Lung | Left Inflamed and Injured Lung | Right Uninflamed and Uninjured Lung | |
| Primary endpoint | ||||
| AUC0–8 h, mg ⋅ h ⋅ L−1 | 26.7 (19.7–39.0)* | 16.0 (13.6–19.9) | 76.0 (68.1–96.0)* | 54.6 (42.7–60.9) |
| Secondary endpoints | ||||
| AUCdialysate/plasma ratio | 0.8 (0.6–0.9)* | 0.4 (0.3–0.5) | 1.2 (1.0–1.4)* | 0.8 (0.6–0.9) |
| Cmax1, mg ⋅ L−1 | 7.4 (5.4–9.5)* | 4.1 (3.6–4.8) | 14.5 (11.2–16.6)* | 9.4 (8.1–11.1) |
| Cmax2, mg ⋅ L−1 | 5.0 (3.7–8.1) | 5.9 (4.7–6.4) | NA | NA |
| Tmax1, min | 80 (80–115) | 80 (80–80) | 120 (100–150) | 80 (80–100) |
| Tmax2, min | 440 (440–455) | 440 (440–440) | NA | NA |
| fT > 4 × MIC, % | 25 (13–53)* | 0 (0–5) | 92 (88–92) | 92 (88–92) |
| fT > 2 × MIC, % | 57 (39–79)* | 22 (17–42) | 92 (92–92) | 92 (92–92) |
| AUCBAL fluid/plasma ratio | 1.1 (0.9–1.4) | 1.1 (0.8–1.4) | 1.1 (0.8–1.1) | 1.0 (0.9–1.1) |
All data were nonparametric paired samples, and the Wilcoxon signed-rank test was used for the entire statistical calculation. Descriptive statistics were expressed as mean ± SD, and pharmacokinetic data were expressed as median and interquartile range. IBM SPSS Statistics, Version 27.0.1.0 (IBM Corporation), was used for all analyses. The significance level was set at P < 0.05.
In addition, we fitted generalized linear mixed models with random intercepts and fixed slopes separately for ceftaroline fosamil and linezolid. The drug concentration in the lungs of the pigs was the dependent variable. The model parameters were estimated taking into account the right and left sides, the upper and lower lobes of the lungs, and the time points of the measurement (see Tables E1–E6 in the online supplement). Generalized linear mixed models do not assume independent observations or take into account the longitudinal nature of the data, between-subjects heterogeneity, and within-subject correlations (23). Missing values were imputed with last observations carried forward. Missing baseline scores were replaced with zero. Multiplicity correction was introduced, and the new significance level was set at 0.004. The models were fitted with Python 3, including the pandas, numpy, and statsmodels libraries.
Six microdialysis probes per pig were successfully placed in all animals (Figure 2A), three in the left lung (upper lobe, mid zone area and lower lobe) and three in the right lung (upper lobe, middle lobe and lower lobe). Unilateral ALI was successfully induced in the left lung in all pigs, as evidenced by macroscopic inspection (Figure 2B) and histological confirmation after the experiment (Figure 3). Additionally, we used an established lung injury score (LIS; see Table E7) (16), which was adapted from the American Thoracic Society guidelines (24), in which 0 is the minimum score without any detectable signs of ALI and 1 is the maximum score with complete lung destruction and all typical findings of ALI present (alveolar edema, proteinaceous debris, hyaline membranes, hemorrhage, and neutrophilic infiltration) (16). The inflamed and injured lungs showed a median LIS of 0.62 (0.58–0.65) compared with a median LIS of 0.14 (0.11–0.15) in the uninflamed and uninjured lungs (P = 0.002; Figure 4). A drop in dynamic compliance less than 50% of the left lung confirmed the presence of ALI at the beginning of the experiment (16). Two pigs died within 1 and 3 hours after induction of ALI because of refractory arrhythmia. The 10 remaining pigs were comparable with respect to hemodynamic, ventilatory, and metabolic parameters (see Tables E8 and E9).
Figure 2. Microdialysis probes in situ (A) before the induction of acute lung injury (ALI) and (B) macroscopic result of ALI at the end of the experiment. (a) The right lung without visible signs of ALI. (b) The damaged left ALI lung. ALI induction occurred in the left lateral decubitus position.
[More] [Minimize]
Figure 3. Histopathological differences in left-to-right comparison. (A) The uninflamed and uninjured right lungs without any visible signs of acute lung injury (ALI), healthy lung parenchyma, and cell-free alveoli. Scale bars: top, 500 μm; middle, 200 μm; and bottom, 100 μm, respectively. (B) The injured and inflamed left lungs with all typical findings of ALI; (a) neutrophilic infiltration, (b) proteinaceous debris, (c) hyaline membranes, (d) hemorrhage, and (e) edema. Scale bars: top, 500 μm; middle, 200 μm; and bottom, 50 μm). *The insertion site of the probe.
[More] [Minimize]
Figure 4. Lung injury score (LIS) in left-to-right comparison. LIS of injured and inflamed lung tissue, indicated in green, compared with LIS of uninflamed and uninjured lung tissue, indicated in gray. Tukey whiskers represent maximum and minimum values.
[More] [Minimize]After intravenous administration of ceftaroline fosamil, dialysate concentrations were different between left inflamed and injured lungs and right uninflamed and uninjured lungs, which persisted until the end of the experiment (Figure 5A and Table 1). Median dialysate area under the concentration curve in the first 8 hours (AUC0–8 h) were higher in inflamed and injured versus uninflamed and uninjured lungs: 26.7 (19.7–39.0) vs. 16.0 (13.6–19.9) mg ⋅ h ⋅ L−1, P = 0.017. Additionally, a generalized linear mixed model was performed to increase power, which confirmed the result (P < 0.001; Table E1). Median Times 1 and 2 to reach peak concentration level (Tmax1 and Tmax2, respectively) were not different between inflamed and injured lungs and uninflamed and uninjured lungs. Median peak concentration level (Cmax) was higher in inflamed and injured lungs after the first dose but not after the second dose. Median fraction of time (fT) > 2 × minimal inhibitory concentration (MIC) and > 4 × MIC and median AUCdialysate/plasma ratios were higher in inflamed and injured lungs. These findings were similar in single-lobe left-to-right comparisons (Figure 6), and tissue concentrations were not different between upper and lower lobes at either side (Figure 7A), which was also confirmed by means of a generalized linear mixed model (Tables E2 and E3). Median left-to-right BALF concentrations were comparable (Figure 8), and AUCBALF/plasma ratios were not different (P = 0.779; Table 1). In a post hoc analysis, each LIS generated has been plotted against every corresponding probe and their ceftaroline fosamil AUC of lung tissue dialysate (see Figure E1A; R2 = 0.403) and against the mean BAL concentrations of the corresponding pig (Figure E1C; R2 = 0.077). A mild correlation is seen in LIS to AUC dialysate but no correlation to BAL concentrations was seen.
Figure 5. Ceftaroline fosamil and linezolid levels in lung tissue and plasma. Concentrations of ceftaroline fosamil (A and C) and linezolid (B and D) in lung tissue (A and B) and in plasma (C and D). Data are presented as means ± SEM. The dotted lines indicate 1× , 2×, and 4× minimal inhibitory concentration.
[More] [Minimize]
Figure 6. Ceftaroline fosamil and linezolid levels in upper lobes (A and C) and lower lobes (B and D). Left-to-right differences in ceftaroline fosamil (A and B) and linezolid (C and D) tissue concentration in the upper and lower lobes. Data are presented as means ± SEM. The dotted lines are 1×, 2×, and 4× minimal inhibitory concentration.
[More] [Minimize]After intravenous administration of linezolid, we found that dialysate concentrations were different between left inflamed and injured lungs and right uninflamed and uninjured lungs, which persisted until the end of the experiment (Figure 5B and Table 1). Median dialysate AUCs0–8 h were higher in inflamed and injured lungs than in uninflamed and uninjured lungs (76.0 [68.1–96.0] vs. 54.6 [42.7–60.9] mg ⋅ h ⋅ L−1; P = 0.011). Additionally, a generalized linear mixed model was performed to increase power, which confirmed the result (P < 0.001; Table E4). Median Tmax values were not different between inflamed and injured lungs and uninflamed and uninjured lungs, but median Cmax, median AUCdialysate/plasma ratios, median fT > 2 × MIC, and median fT > 4 × MIC were significantly higher in inflamed and injured lungs compared with uninflamed and uninjured lungs. There were no differences observed in Tmax and in fT > 2 × MIC and > 4 × MIC. Alike for ceftaroline fosamil, these findings were similar in the separate analysis of single-lobe left-to-right comparisons (Figure 6), and tissue concentrations also were not different between upper and lower lobes at either side (Figure 7B). In the analysis performed additionally by means of a generalized linear mixed model, no difference was also found for the comparison of the upper lobes with the lower lobes on the right side (Figure 7D and Table E5), but a difference was found for the comparison of the upper lobes with the lower lobes on the left side (P < 0.001; Figure 7C and Table E6). Median left-to-right BALF concentrations were comparable (Figure 8), and AUCBALF/plasma ratios were not different (P = 1.000; Table 1). In a post hoc analysis, each LIS generated has been plotted against every corresponding probe and their linezolid AUC of lung tissue dialysate (Figure E1B; R2 = 0.713) and against the mean BAL concentrations of the corresponding pig (Figure E1D; R2 = 0.050). A strong correlation is seen in LIS to AUC dialysate but no correlation to BAL concentrations was found.
Figure 7. Comparison of ceftaroline fosamil and linezolid levels in upper lobes to lower lobes. Data are presented for left (A and C) and right (B and D) lobes. Upper-to-lower lobe differences in ceftaroline fosamil (A and B) and linezolid (C and D) tissue concentration in the inflamed and injured lung compared with the uninflamed and uninjured lung. Data are presented as means ± SEM. The dotted lines indicate 1×, 2×, and 4× minimal inhibitory concentration.
[More] [Minimize]
Figure 8. Ceftaroline fosamil and linezolid levels in BAL fluid. Antimicrobial concentrations in BAL fluid from inflamed and injured lung tissue compared with uninflamed and injured lung tissue at 1 (BAL1), 2 (BAL2), 4 (BAL3), and 7 (BAL4) hours after intravenous administration of ceftaroline fosamil (A) and linezolid (B). Tukey whiskers represent maximum and minimum values. Potential outliers are indicated with a dot. The dotted lines indicate 1×, 2×, and 4× minimal inhibitory concentration.
[More] [Minimize]The findings of this study in a model of unilateral ALI in pigs can be summarized as follows: 1) Median tissue AUCs0–8 h of ceftaroline fosamil and linezolid were higher in inflamed and injured lungs than in uninflamed and uninjured lungs, and so were 2) peak concentrations and 3) AUCdialysate/plasma ratios. This resulted in 4) longer duration > 2 × MIC and > 4 × MIC for ceftaroline fosamil. Of note, 5) AUCBALF/plasma ratios demonstrated a good penetration into ELF for both antimicrobial drugs without any significant side differences.
To the best of our knowledge, we are the first to demonstrate that lung tissue concentrations of two commonly used antimicrobial drugs against pneumonia depend on, and are actually enhanced by, the presence of lung inflammation and injury. Our study has several strengths. To our knowledge, it is the first study comparing the pharmacokinetics of antimicrobial drugs in lung tissue, plasma, and BALF simultaneously in the same animal. We used an established and stable model of unilateral ALI that allowed us to directly compare tissue concentrations in inflamed and injured tissue with uninflamed and uninjured tissue within the same animal. The unilateral model reflects very well the exudative phase of ARDS (1), and we treated the animals with commonly used antimicrobial drugs against pneumonia, at weight-adjusted dosages as used in clinical practice, reaching plasma concentrations comparable with what has been reported in the human setting (21, 25–33). We obtained remarkably similar histological results as in a recently reported combined model of Pseudomonas aeruginosa–induced pneumonia with ventilator-induced lung injury in pigs (34). Indeed, neutrophilic infiltration, edema, hemorrhage, and hyaline membranes as observed in that study was also found in our model. Also important to mention is that the animals in our study did not receive prophylactic treatment with ceftaroline fosamil, linezolid, or any other antimicrobial drug. Thus, all measured concentrations in the different compartments are solely related to the administrations as described in the study protocol. These factors may improve the translatability of the findings of our study to a clinical scenario of pneumonia wherein antimicrobial drugs are essential. We had an analysis plan in place before performing the study, and this plan was strictly followed at all times. Only 2 out of 12 animals died before the end of the experiment.
Our findings are, at least in part in line with results of a previous preclinical investigation (29) and various clinical studies (20, 31, 35–39). Nevertheless, none of these studies measured free drug concentration in ALI compared with healthy tissue. However, changes in microcirculation because of acute inflammation are likely to influence the penetration of antimicrobial agents into the lung tissue, the site of action. One study examined lung tissue levels of ceftaroline fosamil using microdialysis, showing comparable AUCdialysate, AUCdialysate/plasma ratios, plasma Cmax, and AUCplasma (20). However, that study was performed in patients who underwent elective cardiac surgery with cardiopulmonary bypass (i.e., in uninjured lung tissue). There have been no investigations that studied linezolid lung tissue concentrations through microdialysis. As such, the findings of our study add to the existing knowledge on lung tissue concentrations of these antimicrobial drugs.
Our findings are also in line with the studies of other antimicrobial drugs (36–39). In two studies examining lung tissue levels of meropenem (36) and piperacillin (37) in patients who underwent surgery for empyema because of pneumonia, comparable AUCdialysate/plasma ratios were found as in our study in 7 and 5 patients, respectively. However, those authors did not compare their results with antimicrobial concentrations of uninjured lung tissue. In another study in explanted human lung tissue, meropenem AUCdialysate/plasma ratios were lower compared with those in our model (38). However, the explanted lungs exhibited histological signs of fibrosis in contrast to the confirmed histological signs of ALI in our experiments. In patients with sepsis due to pneumonia or pleural empyema that needed surgical resection, comparable AUCdialysate/plasma ratios were found for cefpirome in visually infected lung tissue and visually uninfected tissue (39). However, it must be noted that both microdialysis probes were placed in the same lung lobe and that inflammation was present for a long time in these patients, which could possibly explain the comparable penetration ratios. Additionally, cefpirome penetration ratios in these patients with sepsis were comparable with penetration ratios in healthy subjects in another study (40). There have been no further studies of lung tissue concentrations of other β-lactam antibiotics.
Although it is often suggested that lung tissue concentrations could be too low in inflamed and injured lung tissue (41–44), here we show that tissue concentrations are actually higher at the inflamed and injured sites. After the second bolus administration of ceftaroline fosamil, the disparity observed is less pronounced compared with the initial bolus. One possible explanation could be rooted in the pharmacokinetic characteristics of the antimicrobial drugs of choice. Linezolid possesses a greater volume of distribution and a longer half-life compared with ceftaroline fosamil. Because of its moderate lipophilicity (45), linezolid has the capacity to accumulate intracellularly to some extent (46), rendering it less susceptible to substantial fluid turnover rates. The occasional necessity of administering significant fluid volumes during this study could potentially lead to a dilution effect on highly hydrophilic substances, such as β-lactams. Consequently, this might influence the tissue levels.
Furthermore, we found median AUCBALF/plasma ratios ⩾1 for both antimicrobial drugs in the inflamed and injured lungs as well as in the uninflamed and uninjured lungs. Thus, ceftaroline fosamil and linezolid exhibit excellent penetration into the ELF. This is of great advantage, as the ELF is an important site of action of antimicrobials in bronchopneumonia. Linezolid shows sufficient ELF penetration ratios ⩾1 in several studies (21, 47, 48), which is comparable with our results. Ceftaroline fosamil showed, in a staphylococcal murine pneumonia model, ELF/plasma ratios of approximately 1, which is also in line with our results (29). In contrast, a penetration ratio of only 0.23 was found in healthy subjects (49). Whether this difference in penetration can be attributed to inflammation in the murine model, compared with healthy subjects, has to be confirmed in further studies.
Our study has limitations. We used a model that mimics the exudative phase of ARDS; therefore, we cannot conclude whether differences in tissue concentrations between inflamed and injured lung tissue and uninflamed and uninjured lung tissue also exist at later phases (i.e., in particular, during the fibrotic stage) or when the alveolar architecture and integrity are re-established (1). Future studies in other models are needed to determine whether lung tissue concentrations of ceftaroline fosamil and linezolid are as favorable as shown here. A recently published study of a unilateral infection model with amikacin-resistant and meropenem-susceptible Pseudomonas aeruginosa strains observed no differences in the antibiotic concentrations of meropenem and amikacin in the ELF of infected versus noninfected lungs (50). These findings are in line with our findings of antimicrobial concentrations in the ELF of the inflamed and injured lungs being comparable with those in uninflamed and uninjured lungs. However, intravenously administered antimicrobial penetration into lung tissue was not addressed in this translational promising unilateral infection model. Thus, it remains to be proven whether lung tissue with “real” bacterial infection exhibits fully comparable antibiotic penetration properties as does our model of unilateral ALI.
We found high cytokine levels (IL-6, IL-8) in the ELF of the inflamed and injured as well as in the uninflamed and uninjured lungs in our unilateral ALI model in a previous study (16). However, we did not measure cytokines in the present study, which could be interpreted as a limitation like the missing evaluation of the wet-to-dry ratio of the lungs.
The concomitant administration of two antimicrobial drugs might raise the question of whether interactions between these drugs might have influenced tissue penetration. One of the most common interactions of antimicrobial drugs is driven by protein binding, and only the unbound fraction is effective for treatment (51). However, because both antimicrobial drugs tested here have a low protein binding (35, 52), interactions caused by competitive protein binding is unlikely. Furthermore, our study focused on tissue concentrations early after start of the treatment, and it remains uncertain how tissue concentrations may change after several days of continued administration in bacterial lung infection, limiting the interpretation of our results to the very early phase of lung injury and the initial phase of antimicrobial treatment.
Last but not least, we had no infectious component in our model. Indeed, the pigs suffered from ALI and not pneumonia. Of note, it is difficult to visually distinguish ALI from pneumonia, and we did not take any microbiological cultures from the animals, confirming or ruling out pneumonia. However, we can say with certainty that the development of pathogen-induced pneumonia in young healthy animals within the observation period of 8 hours is highly unlikely.
Tissue drug concentrations of two commonly used antimicrobial drugs were higher in inflamed and injured lungs than in the uninflamed and uninjured lungs in a unilateral model for ALI in pigs. This resulted in longer times above the MIC.
| 1. | Thompson BT, Chambers RC, Liu KD. Acute respiratory distress syndrome. N Engl J Med 2017;377:562–572. |
| 2. | Fan E, Brodie D, Slutsky AS. Acute respiratory distress syndrome: advances in diagnosis and treatment. JAMA 2018;319:698–710. |
| 3. | Papazian L, Klompas M, Luyt CE. Ventilator-associated pneumonia in adults: a narrative review. Intensive Care Med 2020;46:888–906. |
| 4. | Niederman MS. What COVID-19 has taught us: ventilator-associated pneumonia is back! Am J Respir Crit Care Med 2022;206:132–134. |
| 5. | Torres A, Niederman MS, Chastre J, Ewig S, Fernandez-Vandellos P, Hanberger H, et al. International ERS/ESICM/ESCMID/ALAT guidelines for the management of hospital-acquired pneumonia and ventilator-associated pneumonia: guidelines for the management of hospital-acquired pneumonia (HAP)/ventilator-associated pneumonia (VAP) of the European Respiratory Society (ERS), European Society of Intensive Care Medicine (ESICM), European Society of Clinical Microbiology and Infectious Diseases (ESCMID) and Asociación Latinoamericana del Tórax (ALAT). Eur Respir J 2017;50:1700582. |
| 6. | Kalil AC, Metersky ML, Klompas M, Muscedere J, Sweeney DA, Palmer LB, et al. Management of adults with hospital-acquired and ventilator-associated pneumonia: 2016 clinical practice guidelines by the Infectious Diseases Society of America and the American Thoracic Society. Clin Infect Dis 2016;63:e61–e111. |
| 7. | Govindan S, Hyzy RC. The 2016 guidelines for hospital-acquired and ventilator-associated pneumonia. Am J Respir Crit Care Med 2016;195:658–660. |
| 8. | Luyt CE, Bouadma L, Morris AC, Dhanani JA, Kollef M, Lipman J, et al. Pulmonary infections complicating ARDS. Intensive Care Med 2020;46:2168–2183. |
| 9. | Kaye KS, Udeani G, Cole P, Friedland HD. Ceftaroline fosamil for the treatment of hospital-acquired pneumonia and ventilator-associated pneumonia. Hosp Pract (1995) 2015;43:144–149. |
| 10. | Sotgiu G, Aliberti S, Gramegna A, Mantero M, Di Pasquale M, Trogu F, et al. Efficacy and effectiveness of ceftaroline fosamil in patients with pneumonia: a systematic review and meta-analysis. Respir Res 2018;19:205. |
| 11. | Wunderink RG, Roquilly A, Croce M, Rodriguez Gonzalez D, Fujimi S, Butterton JR, et al. A phase 3, randomized, double-blind study comparing tedizolid phosphate and linezolid for treatment of ventilated Gram-positive hospital-acquired or ventilator-associated bacterial pneumonia. Clin Infect Dis 2021;73:e710–e718. |
| 12. | Modi AR, Kovacs CS. Hospital-acquired and ventilator-associated pneumonia: diagnosis, management, and prevention. Cleve Clin J Med 2020;87:633–639. |
| 13. | American Thoracic Society; Infectious Diseases Society of America. Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia. Am J Respir Crit Care Med 2005;171:388–416. |
| 14. | Boselli E, Breilh D, Caillault-Sergent A, Djabarouti S, Guillaume C, Xuereb F, et al. Alveolar diffusion and pharmacokinetics of linezolid administered in continuous infusion to critically ill patients with ventilator-associated pneumonia. J Antimicrob Chemother 2012;67:1207–1210. |
| 15. | Chauzy A, Gregoire N, Ferrandière M, Lasocki S, Ashenoune K, Seguin P, et al. Population pharmacokinetic/pharmacodynamic study suggests continuous infusion of ceftaroline daily dose in ventilated critical care patients with early-onset pneumonia and augmented renal clearance. J Antimicrob Chemother 2022;77:3173–3179. |
| 16. | Geilen J, Kainz M, Zapletal B, Geleff S, Wisser W, Bohle B, et al. Unilateral acute lung injury in pig: a promising animal model. J Transl Med 2022;20:548. |
| 17. | Geilen J, Kainz M, Zapletal B, Jäger W, Zeitlinger M, Tschernko E. Ceftaroline fosamil tissue penetration in a pig model of unilateral acute lung injury: healthy vs injured lung. 2023. Poster P2221. |
| 18. | White BP, Barber KE, Stover KR. Ceftaroline for the treatment of methicillin-resistant Staphylococcus aureus bacteremia. Am J Health Syst Pharm 2017;74:201–208. |
| 19. | Taubert M, Zoller M, Maier B, Frechen S, Scharf C, Holdt L-M, et al. Predictors of inadequate linezolid concentrations after standard dosing in critically ill patients. Antimicrob Agents Chemother 2016;60:5254–5261. |
| 20. | Edlinger-Stanger M, Al Jalali V, Andreas M, Jäger W, Böhmdorfer M, Zeitlinger M, et al. Plasma and lung tissue pharmacokinetics of ceftaroline fosamil in patients undergoing cardiac surgery with cardiopulmonary bypass: an in vivo microdialysis study. Antimicrob Agents Chemother 2021;65:e0067921. |
| 21. | Boselli E, Breilh D, Rimmelé T, Djabarouti S, Toutain J, Chassard D, et al. Pharmacokinetics and intrapulmonary concentrations of linezolid administered to critically ill patients with ventilator-associated pneumonia. Crit Care Med 2005;33:1529–1533. |
| 22. | Rennard SI, Basset G, Lecossier D, O’Donnell KM, Pinkston P, Martin PG, et al. Estimation of volume of epithelial lining fluid recovered by lavage using urea as marker of dilution. J Appl Physiol (1985) 1986;60:532–538. |
| 23. | Carrière I, Bouyer J. Choosing marginal or random-effects models for longitudinal binary responses: application to self-reported disability among older persons. BMC Med Res Methodol 2002;2:15. |
| 24. | Matute-Bello G, Downey G, Moore BB, Groshong SD, Matthay MA, Slutsky AS, et al.; Acute Lung Injury in Animals Study Group. An official American Thoracic Society workshop report: features and measurements of experimental acute lung injury in animals. Am J Respir Cell Mol Biol 2011;44:725–738. |
| 25. | Sazdanovic P, Jankovic SM, Kostic M, Dimitrijevic A, Stefanovic S. Pharmacokinetics of linezolid in critically ill patients. Expert Opin Drug Metab Toxicol 2016;12:595–600. |
| 26. | Helfer VE, Zavascki AP, Zeitlinger M, de Araújo BV, Dalla Costa T. Population pharmacokinetic modeling and probability of target attainment of ceftaroline in brain and soft tissues. Antimicrob Agents Chemother 2022;66:e0074122. |
| 27. | Baldwin DR, Honeybourne D, Wise R. Pulmonary disposition of antimicrobial agents: methodological considerations. Antimicrob Agents Chemother 1992;36:1171–1175. |
| 28. | Buerger C, Plock N, Dehghanyar P, Joukhadar C, Kloft C. Pharmacokinetics of unbound linezolid in plasma and tissue interstitium of critically ill patients after multiple dosing using microdialysis. Antimicrob Agents Chemother 2006;50:2455–2463. |
| 29. | Bhalodi AA, Crandon JL, Biek D, Nicolau DP. Efficacy of ceftaroline fosamil in a staphylococcal murine pneumonia model. Antimicrob Agents Chemother 2012;56:6160–6165. |
| 30. | Dryden M, Zhang Y, Wilson D, Iaconis JP, Gonzalez J. A Phase III, randomized, controlled, non-inferiority trial of ceftaroline fosamil 600 mg every 8 h versus vancomycin plus aztreonam in patients with complicated skin and soft tissue infection with systemic inflammatory response or underlying comorbidities. J Antimicrob Chemother 2016;71:3575–3584. |
| 31. | Justo JA, Mayer SM, Pai MP, Soriano MM, Danziger LH, Novak RM, et al. Pharmacokinetics of ceftaroline in normal body weight and obese (classes I, II, and III) healthy adult subjects. Antimicrob Agents Chemother 2015;59:3956–3965. |
| 32. | Wu C, Zhang X, Xie J, Li Q, He J, Hu L, et al. Pharmacokinetic/pharmacodynamic parameters of linezolid in the epithelial lining fluid of patients with sepsis. J Clin Pharmacol 2022;62:891–897. |
| 33. | Van Wart SA, Forrest A, Khariton T, Rubino CM, Bhavnani SM, Reynolds DK, et al. Population pharmacokinetics of ceftaroline in patients with acute bacterial skin and skin structure infections or community-acquired bacterial pneumonia. J Clin Pharmacol 2013;53:1155–1167. |
| 34. | Barbeta E, Arrieta M, Motos A, Bobi J, Yang H, Yang M, et al. A long-lasting porcine model of ARDS caused by pneumonia and ventilator-induced lung injury. Crit Care 2023;27:239. |
| 35. | MacGowan AP. Pharmacokinetic and pharmacodynamic profile of linezolid in healthy volunteers and patients with Gram-positive infections. J Antimicrob Chemother 2003;51:ii17–ii25. |
| 36. | Tomaselli F, Maier A, Matzi V, Smolle-Jüttner FM, Dittrich P. Penetration of meropenem into pneumonic human lung tissue as measured by in vivo microdialysis. Antimicrob Agents Chemother 2004;48:2228–2232. |
| 37. | Tomaselli F, Dittrich P, Maier A, Woltsche M, Matzi V, Pinter J, et al. Penetration of piperacillin and tazobactam into pneumonic human lung tissue measured by in vivo microdialysis. Br J Clin Pharmacol 2003;55:620–624. |
| 38. | Paal M, Scharf C, Denninger AK, Ilia L, Kloft C, Kneidinger N, et al. Target site pharmacokinetics of meropenem: measurement in human explanted lung tissue by bronchoalveolar lavage, microdialysis, and homogenized lung tissue. Antimicrob Agents Chemother 2021;65:e0156421. |
| 39. | Lindenmann J, Kugler SA, Matzi V, Porubsky C, Maier A, Dittrich P, et al. High extracellular levels of cefpirome in unaffected and infected lung tissue of patients. J Antimicrob Chemother 2011;66:160–164. |
| 40. | Herkner H, Müller MR, Kreischitz N, Mayer BX, Frossard M, Joukhadar C, et al. Closed-chest microdialysis to measure antibiotic penetration into human lung tissue. Am J Respir Crit Care Med 2002;165:273–276. |
| 41. | Stein GE, Wells EM. 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. Curr Med Res Opin 2010;26:571–588. |
| 42. | Stevens DL. The role of vancomycin in the treatment paradigm. Clin Infect Dis 2006;42:S51–S57. |
| 43. | Goldstein F. The potential clinical impact of low-level antibiotic resistance in Staphylococcus aureus. J Antimicrob Chemother 2007;59:1–4. |
| 44. | Sugiyama MG, Mintsopoulos V, Raheel H, Goldenberg NM, Batt JE, Brochard L, et al. Lung ultrasound and microbubbles enhance aminoglycoside efficacy and delivery to the lung in Escherichia coli-induced pneumonia and acute respiratory distress syndrome. Am J Respir Crit Care Med 2018;198:404–408. |
| 45. | Pea F, Furlanut M, Cojutti P, Cristini F, Zamparini E, Franceschi L, et al. Therapeutic drug monitoring of linezolid: a retrospective monocentric analysis. Antimicrob Agents Chemother 2010;54:4605–4610. |
| 46. | Thallinger C, Buerger C, Plock N, Kljucar S, Wuenscher S, Sauermann R, et al. Effect of severity of sepsis on tissue concentrations of linezolid. J Antimicrob Chemother 2008;61: 173–176. |
| 47. | Conte JE Jr, Golden JA, Kipps J, Zurlinden E. Intrapulmonary pharmacokinetics of linezolid. Antimicrob Agents Chemother 2002;46:1475–1480. |
| 48. | Honeybourne D, Tobin C, Jevons G, Andrews J, Wise R. Intrapulmonary penetration of linezolid. J Antimicrob Chemother 2003;51:1431–1434. |
| 49. | Riccobene TA, Pushkin R, Jandourek A, Knebel W, Khariton T. Penetration of ceftaroline into the epithelial lining fluid of healthy adult subjects. Antimicrob Agents Chemother 2016;60:5849–5857. |
| 50. | Motos A, Yang H, Li Bassi G, Yang M, Meli A, Battaglini D, et al. Inhaled amikacin for pneumonia treatment and dissemination prevention: an experimental model of severe monolateral Pseudomonas aeruginosa pneumonia. Crit Care 2023;27:60. |
| 51. | Mehrotra R, De Gaudio R, Palazzo M. Antibiotic pharmacokinetic and pharmacodynamic considerations in critical illness. Intensive Care Med 2004;30:2145–2156. |
| 52. | Principe L, Lupia T, Andriani L, Campanile F, Carcione D, Corcione S, et al. Microbiological, clinical, and PK/PD features of the new anti-Gram-negative antibiotics: β-lactam/β-lactamase inhibitors in combination and cefiderocol—an all-inclusive guide for clinicians. Pharmaceuticals (Basel) 2022;15:463. |
Supported by Medizinische Universität Wien.
Author Contributions: Conception and design: J.G. and E.T. Acquisition of data: J.G., M.K., B.Z., and A.N. Processing of specimens and generation of data: J.T., W.J., and M.B. Analysis and interpretation of data: J.G., M.Z., M.J.S., T.S., V.R., and E.T. Analysis and grading of histopathological specimens: S.G. Drafting or revision of the manuscript: J.G., M.J.S., and E.T. Final approval of the manuscript: J.G., M.K., B.Z., A.N., J.T., W.J., M.B., M.Z., M.J.S., T.S., V.R., S.G., and E.T.
This article has an online supplement, which is accessible from this issue’s table of contents at www.atsjournals.org.
Originally Published in Press as DOI: 10.1164/rccm.202306-0974OC on December 15, 2023
Author disclosures are available with the text of this article at www.atsjournals.org.
