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Published ahead of print on October 11, 2002, doi:10.1164/rccm.200204-363OC
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American Journal of Respiratory and Critical Care Medicine Vol 166. pp. 1375-1381, (2002)
© 2002 American Thoracic Society

Original Article

Lung Deposition and Efficiency of Nebulized Amikacin during Escherichia coli Pneumonia in Ventilated Piglets

Ivan Goldstein, Frederic Wallet, Armelle Nicolas-Robin, Fabio Ferrari, Charles-Hugo Marquette and Jean-Jacques Rouby and the Experimental Intensive Care Unit Study Group

Réanimation Chirurgicale Pierre Viars, Department of Anesthesiology, Pitié-Salpêtrière Hospital, University of Paris VI, Paris; and Department of Bacteriology, DHURE and INSERM U 416, University of Medicine, Lille, France

Correspondence and requests for reprints should be addressed to Jean-Jaques Rouby, Réanimation Chirurgicale Pierre Viars, Department of Anesthesiology, La Pitié-Salpêtrière Hospital, 47-83 boulevard de l'Hôpital, 75013 Paris, France. E-mail: jjrouby.pitie{at}invivo.edu or jean-jacques.rouby{at}psl.ap-hop-paris.fr


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHOD
 RESULTS
 DISCUSSION
 REFERENCES
 
Lung tissue deposition and antibacterial efficiency of nebulized and intravenous amikacin (AMK) were compared in anesthetized and ventilated piglets suffering from a bronchopneumonia produced by the intrabronchial inoculation of Escherichia coli. AMK was administered 24 hours after the inoculation either through an ultrasonic nebulizer (45 mg · kg-1, n = 10) or by intravenous infusion (15 mg · kg-1, n = 8). Piglets were killed 1 hour after a second AMK administration performed 24 hours after the first one, and lung tissue concentrations of AMK and lung bacterial burden were assessed on multiple lung specimens. The amount of nebulized AMK reaching the tracheobronchial tree represented 38 ± 6% of the initial nebulizer AMK charge. After nebulization, AMK lung tissue concentrations were 3- to 30-fold higher than after intravenous administration and were influenced by the severity of lung lesions: 188 ± 175 µg · g-1 in lung segments with mild bronchopneumonia versus 40 ± 65 µg · g-1 in lung segments with severe bronchopneumonia (p < 0.01). Lung bacterial burden was significantly lower in the aerosol group than in the intravenous group (median = 0 colony forming units · g-1 versus median = 5 · 102 colony forming units · g-1, p < 0.001). In conclusion, the deposition of AMK in infected lung parenchyma and the efficiency of bacterial killing were greater after nebulization than after intravenous administration.

Key Words: aerosols • aminoglycosides • piglets • bronchopneumonia • mechanical ventilation


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHOD
 RESULTS
 DISCUSSION
 REFERENCES
 
Ventilator-acquired pneumonia is the most frequent nosocomial infection in the critically ill and affects length and cost of stay in the intensive care unit (1, 2). Gram-negative enteric bacilli often multiresistant to antibiotics are the most frequent causative microorganisms (3). Aminoglycosides, in association with ß-lactams, are commonly used for the treatment of Gram-negative ventilator-acquired pneumonia, and the tissue concentration at the site of infection is a major determinant of the bacterial killing efficiency and clinical response (4, 5). Unfortunately, after a clinically recommended intravenous dose, the aminoglycoside lung tissue deposition is limited because the plasma levels are kept deliberately low to avoid toxicity.

In the mid-1990s, we demonstrated that the intratracheal administration of colistin could significantly reduce the incidence of ventilator-acquired pneumonia in a large series of critically ill patients (6). Recently, using an optimized ultrasonic nebulizer, we found that the administration of aerosolized amikacin (AMK) allowed a high lung deposition in mechanically ventilated piglets with healthy lungs (7). Given the lack of information existing on the deposition of nebulized antibiotics in the infected lung parenchyma, it would be hazardous to extrapolate results obtained in healthy lungs to bronchopneumonic lungs. Human and experimental ventilator-acquired pneumonias are characterized by multiple purulent plugs obstructing distal bronchioles (8–10), and the resulting loss of lung aeration could markedly impair lung deposition of nebulized AMK.

The aim of this study was to compare lung deposition and bactericidal efficiency of nebulized and intravenous AMK in an experimental model of Escherichia coli bronchopneumonia produced in anesthetized piglets mechanically ventilated for prolonged periods of time in an experimental intensive care unit (11–13).


   METHOD
TOP
 ABSTRACT
 INTRODUCTION
 METHOD
RESULTS
 DISCUSSION
 REFERENCES
 
Animal Preparation and Bronchial Inoculation
Twenty-four Largewhite-Landrace piglets (21 ± 2 kg) were anesthetized, orotracheally intubated, and mechanically ventilated in the prone position in the experimental intensive care unit (7, 13). The femoral artery was cannulated for pressure monitoring and blood sampling. Using fiberoptic bronchoscopy, 40 ml of a suspension containing 106 colony forming units (cfu) · ml-1 E. coli, whose minimum inhibitory concentration for AMK was 4 mg · L-1, was selectively inoculated in both lower lobes. The piglets were then ventilated with a fixed tidal volume of 15 ml · kg-1 and no positive end-expiratory pressure. Hemodynamic parameters, airway pressures, blood gases, and respiratory compliance (14) were determined every 3 hours.

Aerosol Generation
An Atomisor MegaHertz ultrasonic nebulizer (Diffusion Technique Française, Saint-Etienne, France), running with a frequency of 2.4 Mhz, was positioned in the inspiratory limb, 40 cm proximal to the Y-piece, and filled with 12 ml of saline containing 45 mg · kg-1 of AMK powder (Bristol-Myers-Squibb, La Défense, France). After completion of nebulization (20 ± 5 min), in each animal, the different parts of the ventilatory circuits, including the nebulizer, were washed separately in a fixed volume of distilled water to assess the amount of deposited AMK. The aerodynamic size distribution of particles was assessed in a separate bench study as previously described (7).

Study Design
Twenty-four hours after the inoculation, the piglets received either an intravenous dose of 15 mg · kg-1 of AMK that was delivered in 30 minutes by an infusion pump (n = 8) or an aerosol of AMK (n = 10). Blood and urine samples were then collected during 24 hours, as previously described (7). A second dose of AMK was given 24 hours later, and animals were killed 1 hour later. Six nontreated inoculated animals (control group) were ventilated during the same period of time to assess reference lung tissue bacterial burden.

Killing and Postmortem Analysis
Immediately after the animals were killed, an exsanguination was performed through direct cardiac puncture, and the lungs were exposed through a cervicothoracic incision. Five "subpleurals" specimens were excised from upper, middle, and lower lobes. Each specimen was divided in three contiguous blocks. On the first cryomixed and homogenized block, AMK tissue concentrations were measured by the immunoenzymatic method with correction for contaminating blood (15). On the second block, quantitative lung tissue bacterial burden was measured according to standard method (16, 17). The third block was used for a histologic study. Bronchopneumonic lesions characterizing each secondary pulmonary lobule were classified into two categories (8, 10): mild bronchopneumonia, defined as the presence of bronchiolitis and/or focal and interstitial bronchopneumonia, or severe bronchopneumonia, defined as the presence of confluent bronchopneumonia and/or necrotizing purulent bronchopneumonia.

Pharmacokinetic Analysis
Urinary and plasma AMK concentrations were measured using an immunoenzymatic assay (TDx; Abbott Laboratories, Abbott Park, IL), and standard kinetic parameters were determined (7, 18). The analysis was computerized using a two-compartment pharmacokinetic open model.

Statistical Analysis
AMK lung tissue concentrations and their regional distribution were analyzed using a two-way analysis of variance for one grouping factor (intravenous or aerosol) and one within factor (lung segment). Relationships between AMK lung tissue concentrations and the histologic grade of bronchopneumonia were analyzed using a Mann-Whitney test. Lung tissue bacterial burden in the aerosol, intravenous, and control groups was compared using a Kruskall-Wallis test followed by a Dunn test. The level of statistical significance was set at p <= 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHOD
 RESULTS
DISCUSSION
 REFERENCES
 
Clinical Findings
Table 1 shows clinical and cardiorespiratory data at baseline, 24 hours after the bacterial inoculation, and 24 hours after the first AMK administration. Animals experienced a progressive and significant deterioration of gas exchange and respiratory mechanics that was not influenced by the treatment. Throughout the experiment, arterial pressure significantly decreased but remained in the normal range in each animal, and no unexpected death occurred.


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  		TABLE 1. Cardiorespiratory parameters at baseline, 24 hours, and 48 hours after the bacterial inoculation

 
Pathologic Findings
The percentage of secondary pulmonary lobules showing a predominance of severe bronchopneumonia was 68, 76, and 79% in the aerosol, intravenous, and control groups (p = NS), respectively. As shown in Figure 1 , the percentage of secondary pulmonary lobules characterized by severe bronchopneumonia was significantly greater in dependent lung segments than in nondependent lung segments.



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  		Figure 1. Percentage of secondary pulmonary lobules showing histologic signs of severe bronchopneumonia (BPN) defined as a predominance of confluent and/or purulent necrotizing BPN. Although the incidence of severe BPN was always lower in the aerosol group (black bars) than in the intravenous group (gray bars), the difference did not reach statistical significance (p = 0.2). Severe BPN was significantly more frequent in dependent (middle lobe, anterior, and posterocaudal segments of lower lobes) than in nondependent (upper lobe and apical segments of lower lobes) lung segments (S6 = apical segment; S8 = anterior segment; S10 = posterocaudal segment).

 
Aerosol Characteristics and Lung Deposition of AMK
At the end of the endotracheal tube, the mass median aerodynamic diameter was 3.4 + 0.2 µm (mean ± geometric SD), and the fraction of particles between 0.5 and 5 µm ranged from 45 to 50%. No coalescence between particles was observed. Of the initial AMK nebulizer charge, 21 ± 5% was retained in the nebulizer's chamber and reservoir, 18 ± 9% was fixed in the inspiratory limb of the respiratory circuits, 5 ± 2% was fixed on the endotracheal tube, and 18 ± 6% deposited in the expiratory filter. The resulting fraction of AMK reaching the respiratory tract was 38 ± 6% of the initial 45 mg · kg-1 deposited in the nebulizer, representing a mean dose of 17 ± 2.8 mg · kg-1 delivered to the respiratory tract, a value slightly greater than the intravenous dose (15 mg · kg-1).

Figure 2 shows the regional distribution of lung tissue concentrations within the infected lung parenchyma. Lung tissue concentrations of AMK in the aerosol group were between 3- to 30-fold higher than those measured in the intravenous group (p < 0.01). In the aerosol group, significantly lower lung tissue concentrations were found in posterocaudal segments of lower lobes as compared with other segments. As illustrated in Figure 3 , lung tissue concentrations were lower in lung segments with severe bronchopneumonia than in lung segments with mild bronchopneumonia; however, AMK deposition in severely infected lung segments remained always significantly greater in the aerosol group than in the intravenous group.



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  		Figure 2. Lung tissue concentrations of AMK measured 1 hour after the second administration performed 48 hours after the bacterial inoculation (aerosol group in black bars, n = 10, and intravenous [IV] group in gray bars, n = 8). AMK lung tissue concentrations were measured on lung specimens representative of each lobe. In the lower lobe, specimens were sampled from dependent (segment 8), nondependent (segment 6), and posterocaudal (segment 10) lung regions. Significant higher lung tissue concentrations were found in lung specimens obtained in animals of the aerosol group. In the aerosol group, AMK lung tissue concentrations were significantly lower in S10 than in the other segments (*p < 0.001). Data are expressed as mean ± SD.

 


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  		Figure 3. AMK lung tissue concentrations according to the histologic grade of bronchopneumonia (BPN) characterizing lung segments in the aerosol (left panel) and intravenous (IV) groups (right panel); n indicates the number of lung segments belonging to each histological category in each group. In the aerosol group, AMK lung tissue concentrations were greater in lung segments with mild BPN than in lung segments with severe BPN (*p < 0.05).

 
Lung Tissue Bacterial Burden
As displayed in Figure 4 , lung specimens from the aerosol group had lower E. coli bacterial counts (median = 0 cfu · g-1 and interquartile range 25/75% = 0–102 cfu · g-1) than lung specimens obtained from the intravenous group (median = 5 · 102 cfu · g-1 and interquartile range = 0–3.5 · 103 cfu · g-1), whereas no difference was found in lung tissue bacterial burden between the intravenous group and the untreated control group (median = 2.5 · 102 cfu · g-1 and interquartile range = 0–1.5 · 103 cfu · g-1). In the aerosol group, 71% of the lung specimens that were cultured were exempt from E. coli versus 16 and 24% of the lung specimens cultured, respectively, in the intravenous and in the untreated control group (p < 0.001).



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  		Figure 4. Lung bacterial burden of E. coli in lung segments collected 1 hour after the second aerosol or intravenous (IV) dose of AMK, or 48 hours after the bacterial inoculation in the untreated control group. Each symbol refers to a single lung specimen. The lung bacterial burden of lung segments is significantly lower in the aerosol group as compared with the IV or control groups (Kruskall Wallis test).

 
Serum and Urine Pharmacokinetics
Pharmacokinetics of AMK plasma concentrations are represented in Figure 5 . The mean peak plasma concentration after AMK administration was 22.5 ± 10 µg · ml-1 in the aerosol group and 36.4 ± 8 µg · ml-1 in the intravenous group (p = NS). AMK plasma concentrations lower than 5 µg · ml-1 were obtained after the sixth hour in both groups. A two-compartment open model with first-order distribution and elimination rates adequately fitted the aerosol and intravenous plasma pharmacokinetics (the correlation coefficients between measured and predicted values were 98 ± 3% and 99 ± 2%). The areas under the serum concentration–time curve in the aerosol and intravenous groups were 87.9 ± 42 mg · h · L-1 and 72 ± 19 mg · h · L-1 (p = NS), respectively. Elimination half-lives of 3.37 ± 0.93 hours and 4.7 ± 0.3 hours were found, respectively, in the aerosol and intravenous group. As shown in Figure 6 , 264 ± 38 mg of nebulized AMK were eliminated in the urines, representing 70 ± 11% of the amount of AMK delivered to the respiratory tract (systemic bioavailability).



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  		Figure 5. Mean AMK plasma concentration time profiles after the end of administration by aerosol (closed circle, n = 10) or by intravenous infusion (open circle, n = 8). Data are expressed as mean ± SD.

 


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  		Figure 6. Fractionated urinary output of AMK between 0 and 3, 3 and 6, 6 and 9, 9 and 12, 12 and 15, 15 and 18, and 18 and 24 hours after nebulization of 45 mg/kg of AMK to 10 piglets. The mean cumulative urinary output of AMK in the corresponding period of time is 264 ± 38 mg. Data are expressed as mean ± SD.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHOD
 RESULTS
 DISCUSSION
REFERENCES
 
This study performed in anesthetized and ventilated piglets with bronchopneumonic lungs shows that tissue concentrations of nebulized AMK achieved in subpleural lung regions were 3- to 30-fold greater than those obtained after an intravenous administration. These impressive differences in the concentrations measured in the infected lung parenchyma were obtained although comparable amounts of AMK reached the upper respiratory tract after nebulization (38% of the initial amount deposited in the nebulizer) and the pulmonary vascular compartment after intravenous administration (100% of the intravenous dose). The excellent lung deposition of nebulized AMK was associated with a greater bactericidal activity: 71% of the lung specimens that were cultured after two daily aerosolizations did not show E. coli growth, whereas in the same conditions, only 16% of the lung specimens were sterile in the intravenous group and 24% in the untreated control group. In contrast with what was observed in piglets with healthy lungs (7), pulmonary deposition of nebulized AMK was not homogeneously distributed depending on the severity of lung infection. In addition, the systemic diffusion of AMK was greater in bronchopneumonic animals than in animals with healthy lungs (7). As a consequence, AMK peak and trough plasma concentrations were in the same range after nebulization and intravenous administration.

Experimental Model of Bronchopneumonia and the Characteristics of Aerosol Delivery
The lung infection experimentally produced in this study closely mimics human ventilator-acquired pneumonia. As previously observed (8, 12, 13), the selective inoculation in the lower lobes of a suspension containing 106 cfu · ml-1 E. coli resulted in a massive and severe infection of caudal and dependant parts of the lungs, whereas upper and nondependant areas were less affected. Similar to critically ill patients (8, 10), lung infection was focally distributed: infected secondary pulmonary lobules were coexisting with noninfected aerated lobules with a clear delineation by interlobular septa (Figure 7) . Attesting to the severity of the experimental bronchopneumonia, the animals experimented upon showed a significant deterioration of gas exchange, respiratory mechanics, and arterial pressure, and the majority of secondary pulmonary lobules showed histologic signs of severe bronchopneumonia. The deterioration of the respiratory status was of a magnitude similar to the one resulting from larger and more concentrated inoculi (13). However, despite the progressive decrease in arterial pressure, the hemodynamic condition was better preserved, and no animal experienced circulatory shock requiring vasopressors.



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  		Figure 7. Histopathological pattern of bronchopneumonic lesions showing the lobular distribution of lung infection. Aerated noninfected lung segments (1) are coexisting with nonaerated bronchopneumonic segments (2–3) characterized by many pseudocysts. Each segment is separated from the other by a well-defined interlobular septa (4). Segment 2 is more severely infected than segment 3.

 
The optimization of the nebulization technique allowed the delivery to the respiratory tract of nearly 40% of the initial AMK deposited into the nebulizer chamber. Such deposition, already observed in animals with healthy lungs (7), is greater than previously reported and likely results from the respect of recommendations aiming at optimizing aerosol delivery (19–22). In addition, technical characteristics of the nebulizer such as quartz vibrations were optimized (operating frequency, 2.4 Mhz) to decrease the mass median aerodynamic diameter below 5 µm (3.4 ± 0.2 µm in this study). It has to be pointed out that the technique of nebulization used in piglets can be easily extended to patients: the ventilator, the ventilatory settings, and the technological environment are the same as in a human intensive care unit. A recent study has shown improved aerosol delivery using a mixture of helium–O2 (23), and it can be speculated that lung deposition could have been further increased by replacing nitrogen with helium.

Lung Tissue, Plasma, and Urine Pharmacokinetics after AMK Nebulization
An excellent AMK deposition was obtained at the site of infection after nebulization. Lung tissue concentrations exceeded the minimum inhibitory concentration of most pathogens involved in human nosocomial infections (3, 24). Most published studies have assessed the antibiotic deposition in bronchial secretions (25–27) or epithelial lining fluid (28); however, very likely, these concentrations are not truly representative of concentrations present in the infected lung parenchyma. In our study, lung specimens harvested in subpleural areas were composed of alveolar structures and distal noncartilaginous bronchioles. As aminoglycosides do not penetrate into cells, the AMK concentrations of our homogenized lung specimens, expressed in µg · g-1 of lung tissue, were influenced by the presence of inflammatory cells, and very likely, the true AMK concentrations present in the infected alveoli were underestimated in lung areas with a high density of polymorphonuclear neutrophils.

Deposition of nebulized AMK was significantly lower in posterocaudal segments of lower lobes characterized by severe bronchopneumonia as compared with upper lobes and apical segments of lower lobes characterized by mild forms of bronchopneumonia. This result differs from the results of our prior study performed in mechanically ventilated piglets with healthy lungs (7) where AMK deposition was homogeneously distributed between the different lung segments (Figure 8) . It has to be pointed out that lung tissue concentrations measured in bronchopneumonic animals were always lower than lung tissue concentrations measured in piglets with healthy lungs. The variable and lower AMK lung deposition may result from the heterogeneity of lung aeration. Experimental bronchopneumonia produced by a direct bronchial inoculation and human ventilator-associated pneumonia is characterized by the presence of multiple purulent plugs obstructing distal bronchioles (8–10) and resulting in a progressive and massive loss of lung aeration. In a recent study (29), we demonstrated that tissue concentrations of inhaled AMK were markedly influenced by lung aeration, a massive loss of aeration resulting in a significant decrease in AMK lung deposition. In the most condensed lung areas, intraparenchymal pseudocysts and severe bronchiolar distension were frequently observed, confirming our previous observations (13). Very likely, such lesions of overdistension resulting from mechanical ventilation represent one of the routes by which nebulized AMK reaches the infected distal lung parenchyma.



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  		Figure 8. Lung tissue concentrations of AMK measured 1 hour after the second daily AMK nebulization in piglets with healthy lungs (black bars, n = 5) and in piglets with infected lungs (gray bars, n = 8), inoculated 24 hours before the first administration with a solution of E. coli. In the lower lobe, specimens were sampled from dependent (segments 6 and 10) and nondependent (segment 8) lung regions. AMK concentrations were homogeneously distributed and significantly higher in piglets with healthy lungs. Data are expressed as mean ± SD (S6 = apical segment; S8 = anterior segment; S10 = postero caudal segment). Data from the five piglets with healthy lungs are taken from a previously published paper (29).

 
A second hypothesis to explain the decrease in AMK tissue concentrations observed in the most severely infected lung regions could be a rapid systemic diffusion of the AMK deposited in the lungs through the damaged alveolocapillary barrier. Lung infection has been shown to increase alveolocapillary barrier permeability (30), which in turn facilitates the diffusion of AMK into the blood stream. Consistent with this hypothesis is the finding that AMK peak plasma concentrations and total urinary excretion, two markers of AMK systemic exposure, were found significantly greater in bronchopneumonic animals (23 ± 10 µg · m-1 and 264 ± 38 mg · day-1) than in piglets with healthy lungs (12 ± 6 µg · ml-1 and 207 ± 76 mg · day-1) (7). In addition, the peak plasma concentration after nebulization of AMK was immediate in bronchopneumonic piglets and delayed in healthy animals, suggesting a rapid systemic absorption from the infected lungs. Moreover, as aminoglycosides are poorly absorbed across mucosal surfaces, the increased systemic bioavailability of inhaled AMK was likely related to an enhanced absorption at the alveolar compartment level rather than in bronchioles (31). As expected, interindividual variability of systemic exposure was high likely because the alveolocapillary barrier was differently affected in each animal. In patients with acute exacerbation of cystic fibrosis, a wide intersubject variability of bronchial deposition and urinary excretion of nebulized aminoglycosides has also been reported (32, 33).

Lung Tissue, Plasma, and Urine Pharmacokinetics after Intravenous AMK
After the intravenous administration of 15 mg · kg-1 AMK, lung tissue concentrations were 4 to 30% of those in animals treated by aerosol and remained always lower than the minimum inhibitory concentration of the most resistive Gram-negative bacteria. Under pathologic conditions, lung deposition of intravenous AMK is variable and depends on the passage through the alveolarcapillary membrane, which may be enhanced by altered permeability (29) or reduced by several factors such as decreased pulmonary perfusion, protein binding, pH, and PaO2 and increased concentrations of protein in the lung parenchyma (34). Because of the limited tissue to plasma concentration ratio of intravenous aminoglycosides in patients with pneumonia (28, 35), it can be speculated that much higher AMK peak plasma concentrations would have been necessary to achieve bactericidal lung tissue concentrations against our E. coli strain, thereby increasing the risk of toxicity; however, the pulmonary deposition of intravenous AMK may be sufficient to achieve bactericidal tissue concentrations for pathogens with lower minimum inhibitory concentration for aminoglycosides.

Lung Bacterial Killing after Nebulized and Intravenous AMK
Twenty-four hours after AMK nebulization, the growth of E. coli strains in the different lung segments was massively inhibited, and 71% of the lung specimens were sterile. This result illustrates the close relationship existing between AMK bactericidal efficiency and lung deposition: the increase in lung tissue concentrations obtained by nebulizing AMK resulted in a massive bacterial killing. Previous studies have reported enhanced bacterial killing and survival rates after nebulized aminoglycosides compared with intramuscular administration in various experimental models such as Pseudomonas aeruginosa pneumonia in guinea pigs (36) or Klebsiella pneumoniae pneumonia in mice (37). This study provides the first evidence of the superiority of aminoglycoside nebulization in a highly relevant model, treated with a device designed to be used in patients. This short-term experiment does not allow assessment of the clinical impact of the enhanced bacterial killing resulting from nebulized AMK: No effect on mortality, clinical response, inflammatory changes, respiratory parameters, and histologic grades of bronchopneumonia could be evidenced to assess the efficacy of aerosol versus intravenous administration or the absence of treatment. A longer period of observation is required to assess the clinical importance of the observed differences in antibacterial efficiency. As intravenous or nebulized AMK was initiated 24 hours after the bronchial inoculation contemporarily to a clinical deterioration, our data clearly indicate that nebulized AMK was active as a treatment and not as a prevention of bronchopneumonia.

In conclusion, despite the severe pulmonary consolidation and loss of aeration observed in bronchopneumonic lung regions, AMK lung tissue deposition remained markedly higher after nebulization than after intravenous administration and resulted in an enhanced and rapid bacterial killing; however, AMK tissue concentrations measured in the bronchopneumonic lungs were lower than previously reported in healthy lungs, and systemic exposure was higher. These encouraging results provide a strong rationale for evaluating the efficiency of nebulized AMK for treating bronchopneumonia in ventilated patients.


   Acknowledgments
 
This study was presented at the Annual Meeting of the Société Française d' Anesthésie-Réanimation (Paris, September 2001) and was awarded as "Le prix du concours des résidents." The authors thank Véronique Connan for the excellent secretariat assistance and Arnold Dive and Michel Pottier for the preparation of the animals. The following members of the Experimental Intensive Care Unit Study Group participated in this study: Guy Aymard and Philippe Lechat, Department of Pharmacology, Pitié-Salpêtrière Hospital, Paris, France; O. Petitjean and Kamel Louchahi, Department of Pharmacology, Avicenne Hospital, Bobigny, France; M.H. Becquemin, Explorations Fonctionelles Respiratoires UPRES 2397, Pitié-Salpêtrière Hospital and Université Paris VII, Paris, France; Gilles Lenaour, Department of Pathology, Pitié-Salpêtrière Hospital, Paris, France; Pierre Coriat, Department of Anesthesiology, Pitié-Salpêtrière Hospital, Paris, France; Qin Lu and Ania Nieszkowska, Réanimation Chirurgicale Pierre Viars, Pitié-Salpêtrière Hospital, Paris, France.


   FOOTNOTES
 
Fabio Ferrari was the recipient of a scholarship provided by the Ministère Français des Affaires Etrangères (ref 315372 K).

This article has an online data supplement, which is accessible from this issue's table of contents online at www.atsjournals.org

Received in original form April 24, 2002; accepted in final form August 6, 2002


   REFERENCES
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 ABSTRACT
 INTRODUCTION
 METHOD
 RESULTS
 DISCUSSION
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