The quantitative distribution of nebulized antibiotic in the lung in cystic fibrosis

Genotoxic Agents Produce Stressor-Specific Spectra of Spectinomycin Resistance Mutations Based on Mechanism of Action and Selection in Bacillus subtilis

Mutagenesis is integral for bacterial evolution and the development of antibiotic resistance. Environmental toxins and stressors are known to elevate the rate of mutagenesis through direct DNA toxicity, known as stress-associated mutagenesis, or via a more general stress-induced process that relies on intrinsic bacterial pathways. Here, we characterize the spectra of mutations induced by an array of different stressors using high-throughput sequencing to profile thousands of spectinomycin-resistant colonies of Bacillus subtilis. We found 69 unique mutations in the rpsE and rpsB genes, and that each stressor leads to a unique and specific spectrum of antibiotic-resistance mutations. While some mutations clearly reflected the DNA damage mechanism of the stress, others were likely the result of a more general stress-induced mechanism. To determine the relative fitness of these mutants under a range of antibiotic selection pressures, we used multistrain competitive fitness experiments and found an additional landscape of fitness and resistance. The data presented here support the idea that the environment in which the selection is applied (mutagenic stressors that are present), as well as changes in local drug concentration, can significantly alter the path to spectinomycin resistance in B. subtilis.

Filamentous Bacteriophages and the Competitive Interaction between Pseudomonas aeruginosa Strains under Antibiotic Treatment: a Modeling Study

Pseudomonas aeruginosa (Pa) is a major bacterial pathogen responsible for chronic lung infections in cystic fibrosis patients. Recent work has implicated Pf bacteriophages, nonlytic filamentous viruses produced by Pa, in the chronicity and severity of Pa infections. Pf phages act as structural elements in Pa biofilms and sequester aerosolized antibiotics, thereby contributing to antibiotic tolerance. Consistent with a selective advantage in this setting, the prevalence of Pf-positive (Pf+) bacteria increases over time in these patients. However, the production of Pf phages comes at a metabolic cost to bacteria, such that Pf+ strains grow more slowly than Pf-negative (Pf-) strains in vitro. Here, we use a mathematical model to investigate how these competing pressures might influence the relative abundance of Pf+ versus Pf- strains in different settings. Our model suggests that Pf+ strains of Pa cannot outcompete Pf- strains if the benefits of phage production falls onto both Pf+ and Pf- strains for a majority of parameter combinations. Further, phage production leads to a net positive gain in fitness only at antibiotic concentrations slightly above the MIC (i.e., concentrations for which the benefits of antibiotic sequestration outweigh the metabolic cost of phage production) but which are not lethal for Pf+ strains. As a result, our model suggests that frequent administration of intermediate doses of antibiotics with low decay rates and high killing rates favors Pf+ over Pf- strains. These models inform our understanding of the ecology of Pf phages and suggest potential treatment strategies for Pf+ Pa infections. IMPORTANCE Filamentous phages are a frontier in bacterial pathogenesis, but the impact of these phages on bacterial fitness is unclear. In particular, Pf phages produced by Pa promote antibiotic tolerance but are metabolically expensive to produce, suggesting that competing pressures may influence the prevalence of Pf+ versus Pf- strains of Pa in different settings. Our results identify conditions likely to favor Pf+ strains and thus antibiotic tolerance. This study contributes to a better understanding of the unique ecology of filamentous phages in both environmental and clinical settings and may facilitate improved treatment strategies for combating antibiotic tolerance.

Liquid Chromatography Mass Spectrometry Detection of Antibiotic Agents in Sputum from Persons with Cystic Fibrosis

Antibiotic therapy is expected to impact host microbial communities considerably, yet many studies focused on microbiome and health are often confounded by limited information about antibiotic exposure. Given that antibiotics have diverse pharmacokinetic and antimicrobial properties, investigating the type and concentration of these agents in specific host specimens would provide much needed insight into their impact on the microbes therein. Here, we developed liquid chromatography mass spectrometry (LC-MS) methods to detect 18 antibiotic agents in sputum from persons with cystic fibrosis. Antibiotic spike-in control samples were used to compare three liquid extraction methods on the Waters Acquity Quattro Premier XE. Extraction with dithiothreitol captured the most antibiotics and was used to detect antibiotics in sputum samples from 11 people with cystic fibrosis, with results being compared to the individuals' self-reported antibiotic use. For the sputum samples, two LC-MS assays were used; the Quattro Premier detected nanomolar or micromolar concentrations of 16 antibiotics, whereas the Xevo TQ-XS detected all 18 antibiotics, most at subnanomolar levels. In 45% of tested sputum samples (71/158), at least one antibiotic that was not reported by the subject was detected by both LC-MS methods, a discordance largely explained by the thrice weekly administration and long half-life of azithromycin. For ∼37% of samples, antibiotics reported as taken by the individual were not detected by either instrument. Our results provide an approach for detecting a variety of antibiotics at the site of infection, thereby providing a means to include antibiotic usage data into microbiome studies.

Surfactant-induced spreading of nanoparticles is inhibited on mucus mimetic surfaces that model native lung conditions

We investigated the ability of surfactant-induced spreading to promote nanoparticle distribution on model mucus hydrogels. The hydrogels were formulated with viscoelastic properties and surface tensions that match those of native lung mucus. Nanoparticle-containing droplets with or without surfactant were deposited on the mucus surface and spreading patterns were monitored by time-course fluorescence imaging. Overall, surfactant-induced spreading of nanoparticles required an appropriate balance between Marangoni forces and viscoelastic subphase resistance. Spreading was enhanced on bare gels by increasing the concentration of surfactant in the droplets or reducing the viscoelastic properties of the subphase. However, with a pre-existing film of pulmonary surfactant on the mucus surface, spreading was dramatically inhibited as the surface tension gradient between the droplets and the surrounding subphase decreased. A complete lack of spreading was observed at surface tensions that matched those in the tracheobronchial region of the lungs, even with full-concentration Infasurf. These studies demonstrate that the magnitude of spreading on lung mucus-like surfaces is limited by native mucosal properties.

A research pathway for the study of the delivery and disposition of nebulised antibiotics: an incremental approach from in vitro to large animal models

Background

Nebulised antibiotics are frequently used for the prevention or treatment of ventilator-associated pneumonia. Many factors may influence pulmonary drug concentrations with inaccurate dosing schedules potentially leading to therapeutic failure and/or the emergence of antibiotic resistance. We describe a research pathway for studying the pharmacokinetics of a nebulised antibiotic during mechanical ventilation using in vitro methods and ovine models, using tobramycin as the study antibiotic.

Methods

In vitro studies using a laser diffractometer and a bacterial-viral filter were used to measure the effect of the type and size of tracheal tubes and antibiotic concentration on the particle size distribution of the tobramycin 400 mg (4 ml; 100 mg/ml) and 160 mg (4 ml, 40 mg/ml) aerosol and nebulised mass delivered. To compare the regional drug distribution in the lung of two routes (intravenous and nebulised) of drug administration of tobramycin 400 mg, technetium-99m-labelled tobramycin 400 mg with planar nuclear medicine imaging was used in a mechanically ventilated ovine model. To measure tobramycin concentrations by intravenous and nebulised tobramycin 400 mg (4 ml, 100 mg/ml) administration in the lung interstitial space (ISF) fluid and blood of mechanically ventilated sheep, the microdialysis technique was used over an 8-h duration.

Results

Tobramycin 100 mg/ml achieved a higher lung dose (121.3 mg) compared to 40 mg/ml (41.3 mg) solution. The imaging study with labelled tobramycin indicated that nebulised tobramycin distributed more extensively into each lung zone of the mechanically ventilated sheep than intravenous administration. A higher lung ISF peak concentration of tobramycin was observed with nebulised tobramycin (40.8 mg/l) compared to intravenous route (19.0 mg/l).

Conclusions

The research methods appear promising to describe lung pharmacokinetics for formulations intended for nebulisation during mechanical ventilation. These methods need further validation in an experimental pneumonia model to be able to contribute toward optimising dosing regimens to inform clinical trials and/or clinical use.

The topical study of inhaled drug (salbutamol) delivery in idiopathic pulmonary fibrosis

Background

Our aim was to investigate total and regional lung delivery of salbutamol in subjects with idiopathic pulmonary fibrosis (IPF).

Methods

The TOPICAL study was a 4-period, partially-randomised, controlled, crossover study to investigate four aerosolised approaches in IPF subjects. Nine subjects were randomised to receive ^99mTechnetium-labelled monodisperse salbutamol (1.5 μm or 6 μm; periods 1 and 2). Subjects also received radio-labelled salbutamol using a polydisperse nebuliser (period 3) and unlabelled salbutamol (400 μg) using a polydisperse pressurized metered dose inhaler with volumatic spacer (pMDI; period 4).

Results

Small monodisperse particles (1.5 μm) achieved significantly better total lung deposition (TLD, mean % ± SD) than larger particles (6 μm), where polydisperse nebulisation was poor; (TLD, 64.93 ± 10.72; 50.46 ± 17.04; 8.19 ± 7.72, respectively). Small monodisperse particles (1.5 μm) achieved significantly better lung penetration (mean % ± SD) than larger particles (6 μm), and polydisperse nebulisation showed lung penetration similar to the small particles; PI (mean ± SD) 0.8 ± 0.16, 0.49 ± 0.21, and 0.73 ± 0.19, respectively. Higher dose-normalised plasma salbutamol levels were observed following monodisperse 1.5 μm and 6 μm particles, compared to polydisperse pMDI inhalation, while lowest plasma levels were observed following polydisperse nebulisation.

Conclusion

Our data is the first systematic investigation of inhaled drug delivery in fibrotic lung disease. We provide evidence that inhaled drugs can be optimised to reach the peripheral areas of the lung where active scarring occurs in IPF.

Trial registration

This trial was registered on clinicaltrials.gov (NCT01457261).

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0732-0) contains supplementary material, which is available to authorized users.

The Rationale and Evidence for Use of Inhaled Antibiotics to Control Pseudomonas aeruginosa Infection in Non-cystic Fibrosis Bronchiectasis

Non-cystic fibrosis bronchiectasis (NCFBE) is a chronic inflammatory lung disease characterized by irreversible dilation of the bronchi, symptoms of persistent cough and expectoration, and recurrent infective exacerbations. The prevalence of NCFBE is on the increase in the United States and Europe, but no licensed therapies are currently available for its treatment. Although there are many similarities between NCFBE and cystic fibrosis (CF) in terms of respiratory symptoms, airway microbiology, and disease progression, there are key differences, for example, in response to treatment, suggesting differences in pathogenesis. This review discusses possible reasons underlying differences in response to inhaled antibiotics in people with CF and NCFBE. Pseudomonas aeruginosa infections are associated with the most severe forms of bronchiectasis. Suboptimal levels of antibiotics in the lung increase the mutation frequency of P. aeruginosa and lead to the development of mucoid strains characterized by formation of a protective polysaccharide biofilm. Mucoid strains of P. aeruginosa are associated with a chronic infection stage, requiring long-term antibiotic therapy. Inhaled antibiotics provide targeted delivery to the lung with minimal systemic toxicity and adverse events compared with oral/intravenous routes of administration, and they could be alternative treatment options to help address some of the treatment challenges in the management of severe cases of NCFBE. This review provides an overview of completed and ongoing trials that evaluated inhaled antibiotic therapy for NCFBE. Recently, several investigators conducted phase 3 randomized controlled trials with inhaled aztreonam and ciprofloxacin in patients with NCFBE. While the aztreonam trial results were not associated with significant clinical benefit in NCFBE, initial results reported from the inhaled ciprofloxacin (dry powder for inhalation and liposome-encapsulated/dual-release formulations) trials hold promise. A more targeted approach could identify specific populations of NCFBE patients who benefit from inhaled antibiotics.

Effects of Emulsion Composition on Pulmonary Tobramycin Delivery During Antibacterial Perfluorocarbon Ventilation

BACKGROUND

The effectiveness of inhaled aerosolized antibiotics is limited by poor ventilation of infected airways. Pulmonary delivery of antibiotics emulsified within liquid perfluorocarbon [antibacterial perfluorocarbon ventilation (APV)] may solve this problem through better airway penetration and improved spatial uniformity. However, little work has been done to explore emulsion formulation and the corresponding effects on drug delivery during APV. This study investigated the effects of emulsion formulation on emulsion stability and the pharmacokinetics of antibiotic delivery via APV.

METHODS

Gravity-driven phase separation was examined in vitro by measuring emulsion tobramycin concentrations at varying heights within a column of emulsion over 4 hours for varying values of fluorosurfactant concentration (Cfs = 5-48 mg/mL H2O). Serum and pulmonary tobramycin concentrations in rats were then evaluated following pulmonary tobramycin delivery via aerosol or APV utilizing sufficiently stable emulsions of varying aqueous volume percentage (Vaq = 1%-5%), aqueous tobramycin concentration (Ct = 20-100 mg/mL), and Cfs (15 and 48 mg/mL H2O).

RESULTS

In vitro assessment showed sufficient spatial and temporal uniformity of tobramycin dispersion within emulsion for Cfs ≥15 mg/mL H2O, while lower Cfs values showed insufficient emulsification even immediately following preparation. APV with stable emulsion formulations resulted in 5-22 times greater pulmonary tobramycin concentrations at 4 hours post-delivery relative to aerosolized delivery. Concentrations increased with emulsion formulations utilizing increased Vaq (with decreased Ct) and, to a lesser extent, increased Cfs.

CONCLUSIONS

The emulsion stability necessary for effective delivery is retained at Cfs values as low as 15 mg/mL H2O. Additionally, the pulmonary retention of antibiotic delivered via APV is significantly greater than that of aerosolized delivery and can be most effectively increased by increasing Vaq and decreasing Ct. APV has been further proven as an effective means of pulmonary drug delivery with the potential to significantly improve antibiotic therapy for lung disease patients.

Density-dependent adaptive resistance allows swimming bacteria to colonize an antibiotic gradient

During antibiotic treatment, antibiotic concentration gradients develop. Little is know regarding the effects of antibiotic gradients on populations of nonresistant bacteria. Using a microfluidic device, we show that high-density motile Escherichia coli populations composed of nonresistant bacteria can, unexpectedly, colonize environments where a lethal concentration of the antibiotic kanamycin is present. Colonizing bacteria establish an adaptively resistant population, which remains viable for over 24 h while exposed to the antibiotic. Quantitative analysis of multiple colonization events shows that collectively swimming bacteria need to exceed a critical population density in order to successfully colonize the antibiotic landscape. After colonization, bacteria are not dormant but show both growth and swimming motility under antibiotic stress. Our results highlight the importance of motility and population density in facilitating adaptive resistance, and indicate that adaptive resistance may be a first step to the emergence of genetically encoded resistance in landscapes of antibiotic gradients.

Pharmacokinetic and pharmacodynamic implications in inhalable antimicrobial therapy

Inhaled antimicrobials provide a promising alternative to the systemically delivered drugs for the treatment of acute and chronic lung infections. The delivery of antimicrobials via inhalation route decreases the systemic exposure while increasing the local concentration in the lungs, enabling the use of antimicrobials with severe systemic side effects. The inhalation route of administration has several challenges in pharmacokinetic (PK) and pharmacodynamic (PD) assessments. This review discusses various issues that need to be considered during study, data analysis, and interpretation of PK and PD of inhaled antimicrobials. Advancements overcoming the challenges are also discussed.

Clinical applications of pulmonary delivery of antibiotics

The treatment of infection typically involves administration of antibiotics by a systemic route, such as intravenous or oral. However, pulmonary infections can also be approached by inhalation of antibiotics as the infection is more directly accessible via the airways, making inhalation delivery essentially topical administration. This approach offers deposition of high antimicrobial concentrations directly at the site of infection but with a potentially reduced systemic exposure. This review covers the evidence for aerosolized antibiotics for the treatment of a number of conditions such as cystic fibrosis (CF), where it has become the standard of care for chronic infection, as well as non-CF bronchiectasis, non-tuberculous mycobacteria, and ventilator-associated infection where such therapy does not have an approved indication but has been used with increasing frequency.

Antimicrobial and biophysical properties of surfactant supplemented with an antimicrobial peptide for treatment of bacterial pneumonia

Antibiotic-resistant bacterial infections represent an emerging health concern in clinical settings, and a lack of novel developments in the pharmaceutical pipeline is creating a "perfect storm" for multidrug-resistant bacterial infections. Antimicrobial peptides (AMPs) have been suggested as future therapeutics for these drug-resistant bacteria, since they have potent broad-spectrum activity, with little development of resistance. Due to the unique structure of the lung, bacterial pneumonia has the additional problem of delivering antimicrobials to the site of infection. One potential solution is coadministration of AMPs with exogenous surfactant, allowing for distribution of the peptides to distal airways and opening of collapsed lung regions. The objective of this study was to test various surfactant-AMP mixtures with regard to maintaining pulmonary surfactant biophysical properties and bactericidal functions. We compared the properties of four AMPs (CATH-1, CATH-2, CRAMP, and LL-37) suspended in bovine lipid-extract surfactant (BLES) by assessing surfactant-AMP mixture biophysical and antimicrobial functions. Antimicrobial activity was tested against methillicin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. All AMP/surfactant mixtures exhibited an increase of spreading compared to a BLES control. BLES+CATH-2 mixtures had no significantly different minimum surface tension versus the BLES control. Compared to the other cathelicidins, CATH-2 retained the most bactericidal activity in the presence of BLES. The BLES+CATH-2 mixture appears to be an optimal surfactant-AMP mixture based on in vitro assays. Future directions involve investigating the potential of this mixture in animal models of bacterial pneumonia.

Case studies of the spatial heterogeneity of DNA viruses in the cystic fibrosis lung

Microbial communities in the lungs of patients with cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) have been shown to be spatially heterogeneous. Viral communities may also vary spatially, leading to localized viral populations and infections. Here, we characterized viral communities from multiple areas of the lungs of two patients with late-stage CF using metagenomics, that is, the explanted lungs from a transplant patient and lungs acquired postmortem. All regions harbored eukaryotic viruses that may infect the human host, notably herpesviruses, anelloviruses, and papillomaviruses. In the highly diseased apical lobes of explant lungs, viral diversity was extremely low, and only eukaryotic viruses were present. The absence of phage suggests that CF-associated microbial biofilms may escape top-down controls by phage predation. The phages present in other lobes of explant lungs and in all lobes of postmortem lungs comprised distinct communities, and encoded genes for clinically important microbial phenotypes, including small colony variants and antibiotic resistance. Based on the these observations, we postulate that viral communities in CF lungs are spatially distinct and contribute to CF pathology by augmenting the metabolic potential of resident microbes, as well as by directly damaging lung tissue via carcinomas and herpesviral outbreaks.

A comparison of amount and speed of deposition between the PARI LC STAR® jet nebulizer and an investigational eFlow® nebulizer

BACKGROUND

The potency and physical properties of many of the drugs used in the treatment of cystic fibrosis necessitates the use of nebulization, a relatively time-consuming pulmonary delivery method. Newer, faster, and more efficient delivery systems are being proposed. The purposes of this study was to compare the length of time it took to deliver the equivalent of normal saline nebulized for 10 min in a PARI LC STAR(®) nebulizer to that of an investigational PARI eFlow(®).

METHODS

Six normal adults inhaled a 4-mL (36-mg) charge volume of saline from the LC STAR(®) or a 2.5-mL (22.5-mg) charge volume from the investigational eFlow(®). The saline was mixed with (99m)Tc-DTPA to allow two-dimensional imaging. The inhalation was preceded by a xenon equilibration scan to allow more accurate separation of deposition into central and peripheral lung regions.

RESULTS

The investigational eFlow(®) delivered 8.6 ± 1.0 mg, approximately 90% of the lung dose compared to the LC STAR(®), 9.6 ± 1.0 mg, but did in less than half the time (p < 0.02 for both). There were no differences in central versus peripheral distribution for either device.

CONCLUSIONS

In conclusion the investigational eFlow(®) was both faster and more efficient than the LC STAR(®).

Evaluation of the Target Inhalation Mode (TIM) breathing maneuver in simulated nebulizer therapy in patients with cystic fibrosis

BACKGROUND

Adaptive Aerosol Delivery (AAD) systems provide efficient drug delivery and improved lung deposition over conventional nebulizers by combining real-time analyses of patient breathing patterns and precisely timed aerosol delivery. Delivery and deposition are further enhanced by breathing techniques involving slow, deep inhalations.

METHODS

This exploratory study assessed the acceptability of slow, deep inhalations in 20 patients with cystic fibrosis (CF) during up to eight simulated nebulizer treatments with the I-neb AAD System. The breathing maneuver, Target Inhalation Mode (TIM) breathing, involved the lengthening of the patient's inhalation time over successive breaths with guidance from auditory and tactile (vibratory) feedback from the device.

RESULTS

At the end of the first treatment, most patients felt that the instructions were easy to understand (90%) and that the vibratory feedback was pleasant (65%). Half of the patients found the procedure to be comfortable. At the end of the final treatment, most patients felt that the breathing maneuver was easy to understand (90%) and use (80%), but that the duration of the breath was too long (100%). Logged data revealed that 90% of patients were able to comply with the breathing maneuver. The two patients unable to comply had a forced vital capacity of <1.75 L. The average treatment time decreased from 288.4 to 141.6 sec during the first and final treatments, respectively.

CONCLUSIONS

This study provides preliminary evidence of the acceptability of the TIM breathing maneuver in patients with CF and their ability to perform repeated TIM breathing during simulated nebulizer therapy with the I-neb AAD System.

Aerosol drug delivery in lung transplant recipients

BACKGROUND

Inhaled drug delivery after lung transplantation provides a unique opportunity for direct treatment of a solid organ transplant. At present, no inhaled therapies are approved for this population though several have received some development. Primary potential applications include inhaled immunosuppressive and anti-infective drugs.

OBJECTIVES

The objective of this article is to review potential applications of inhaled medications for lung transplant recipients, the techniques used to develop inhaled drugs and the challenges of aerosol delivery in this specific population.

METHODS

The results of relevant studies are reviewed and two developmental examples are presented.

RESULTS/CONCLUSIONS

Inhaled medications may provide significant advantages for lung transplant recipients. Past studies with inhaled cyclosporine and amphotericin-B provide useful guidance for clinical development of new preparations.

Pulmonary deposition of inhaled tobramycin prior to and after respiratory therapy and use of inhaled albuterol in cystic fibrosis patients colonized with Pseudomonas aeruginosa

OBJECTIVE

To evaluate whether respiratory therapy followed by the use of inhaled albuterol modifies the pulmonary deposition of inhaled tobramycin in patients with cystic fibrosis (CF) and whether pulmonary deposition correlates with disease severity or genotype.

METHODS

A prospective study was carried out including patients with CF older than 6 years of age and colonized with Pseudomonas aeruginosa. Exclusion criteria were pulmonary exacerbation, changes in therapy between the study phases and FEV1 < 25%. All patients were submitted to pulmonary scintigraphy by means of a scintillation camera equipped with a low energy all purpose collimator in order to evaluate drug penetration following the administration of inhaled 99mTc-tobramycin, as well as to pulmonary perfusion with 99mTc-macroaggregated albumin (phase 1). One month later, the same procedure was performed following respiratory therapy and administration of inhaled albuterol (phase 2).

RESULTS

We included 24 patients (12 males) aged 5-27 years (mean +/- SD: 12.85 +/- 6.64 years). The Shwachman score (SS) was excellent/good in 8 patients, moderate/fair in 16 and poor in 0. Genotyping revealed that 7 patients were DeltaF508 homozygotes, 13 were DeltaF508 heterozygotes; and 4 presented other mutations. In all patients, lung deposition of tobramycin decreased in phase 2, especially in those with moderate/fair SS (p = 0.017) and in heterozygotes (p = 0.043).

CONCLUSIONS

The use of a respiratory therapy technique and the administration of inhaled albuterol immediately prior to the use of inhaled tobramycin decreased the pulmonary deposition of the latter in CF patients, and this reduction correlates with disease severity and genotype.

Modulation of secreted virulence factor genes by subinhibitory concentrations of antibiotics in Pseudomonas aeruginosa

Recent studies have shown that subinhibitory antibiotics play important roles in regulating bacterial genes including virulence factor genes. In this study, the expression of 13 secreted virulence related gene clusters of Pseudomonas aeruginosa, an important opportunistic pathogen, was examined in the presence of subinhibitory concentrations of 4 antibiotics: vancomycin, tetracycline, ampicillin and azithromycin. Activation of gene expression was observed with phzAl, rhlAB, phzA2, lasB, exoY, and exoS. Subinhibitory concentrations of vancomycin resulted in more than 10-fold increase of rhlAB and phzA2 transcription. Both rhamnolipid production and pyocyanin production were significantly elevated, correlating phenotypes with the increased transcription. P. aeruginosa swarming and swimming motility also increased. Similar results were observed with subinhibitory tetracycline, azithromycin and ampicillin. These results indicate that the antibiotics at low concentrations can up-regulate virulence factors and therefore influence bacterial pathogenesis.

Rapid pulmonary delivery of inhaled tobramycin for Pseudomonas infection in cystic fibrosis: a pilot project

BACKGROUND

Patients with cystic fibrosis spend as much 30 min a day inhaling tobramycin. Could a new rapid system deposit the equivalent amount of tobramycin faster?

METHODS

Six healthy adult males inhaled 5 ml (300 mg) of tobramycin from a breath enhanced nebulizer and either 125 mg (n = 3) or 150 mg (n = 3) from a vibrating membrane system with a large or small aerosol mixing chamber respectively. A radiolabel was added to the solution and shown to "track" with the tobramycin. Imaging was done with a dual headed gamma camera. Because the radiolabel will be cleared by mucociliary action during administration, algorithms were developed to allow the comparison of a slower system to a faster one.

RESULTS

Both formulations were well tolerated. The lung deposition was 16.6 +/- 3.2% (mean +/- SD) of the charge dose delivered in 10.9 +/- 1.0 min for the breath enhanced nebulizer versus 32.0 +/- 5.1% delivered in 2.5 +/- 0.4 min from the vibrating membrane system. The absolute pulmonary delivery of tobramycin was 49.9 +/- 9.6 versus 43.9 +/- 4.8 mg for the two systems respectively, differences that were statistically significant (pair t-test) but unlikely to be clinically significant. There was a similar deposition of tobramycin for the 125 and 150 mg dose.

CONCLUSIONS

It is possible to deliver an equivalent amount of tobramycin in a shorter period of time with the new vibrating membrane system and a more concentrated formulation. These data will allow the design of a comparison in patients with CF.

Disease guided optimization of the respiratory delivery of microparticulate formulations

BACKGROUND

Inhalation of microparticulate dosage forms can be effectively used in the treatment of respiratory and systemic diseases.

OBJECTIVE

Disease states investigated for treatment by inhalation of microparticles were reviewed along with the drugs' pharmacological, pharmacokinetic and physical chemical properties to identify the advantages of microparticulate inhalation formulations and to identify areas for further improvement.

METHODS

Microbial infections of the lung, asthma, diabetes, lung transplantation and lung cancer were examined, with a focus on those systems intended to provide a sustained release.

CONCLUSION

In developing microparticulate formulations for inhalation in the lung, there is a need to understand the pharmacology of the drug as the key to revealing the optimal concentration time profile, the disease state, and the pharmacokinetic properties of the pure drug as determined by IV administration and inhalation. Finally, in vitro release studies will allow better identification of the best dosing strategy to be used in efficacy and safety studies.

Pharmacoscintigraphic and pharmacokinetic evaluation of tobramycin DPI formulations in cystic fibrosis patients

Tobramycin dry powder formulations were evaluated by gamma scintigraphy and pharmacokinetic methods. In an open single-dose, three-treatment, three-period, cross-over study, nine cystic fibrosis patients received both the two test products and the reference product Tobi (nebulizer solution) in order to assess lung deposition and systemic comparative bioavailability of the two investigational inhaled products versus the marketed inhaled comparator product. The percentage of dose (mean+/-SD) in the whole lung was 53.0+/-10.0% for the tobramycin Form 1, 34.1+/-12.4% for the tobramycin Form 2 and 7.6+/-2.7% for the comparator product Tobi. Lung deposition expressed as a percentage of the nominal dose was thus estimated to be 7.0 and 4.5 times higher for the Tobra Form 1 and Tobra Form 2 than for the Tobi, respectively. Furthermore, the systemic bioavailability (adjusted to correspond to the same drug dose as that of the comparator product deposited in the lung) was found to be 1.6 times higher for the comparator product Tobi than for the two DPI formulations. The principal advantages of the DPI formulations include reduced systemic availability and thus, side effects, and higher dose levels of the drug at the site of drug action.

Calculating expected lung deposition of aerosolized administration of AAV vector in human clinical studies

BACKGROUND

Cystic fibrosis is an autosomal recessive disease affecting approximately 1 in 2500 live births. Introducing the cDNA that codes for normal cystic fibrosis transmembrane conductance regulator (CFTR) to the small airways of the lung could result in restoring the CFTR function. A number of vectors for lung gene therapy have been tried and adeno-associated virus (AAV) vectors offer promise. The vector is delivered to the lung using a breath-actuated jet nebulizer. The purpose of this project was to determine the aerosolized AAV (tgAAVCF) particle size distribution (PSD) in order to calculate target doses for lung delivery.

METHODS

A tgAAVCF solution was nebulized using the Pari LC Plus (n = 3), and the PSD was determined by coupling laser diffraction and inertial impaction (NGI) techniques. The NGI allowed for quantification of the tgAAVCF at each stage of impaction, ensuring that rAAV-CFTR vector is present and not empty particles. Applying the results to mathematical algorithms allowed for the calculation of expected pulmonary deposition.

RESULTS

The mass median diameter (MMD) for the tgAAVCF was 2.78 +/- 0.43 microm. If the system works ideally and the patient only receives aerosol on inspiration, the patient would receive 47 +/- 0% of the initial dose placed in the nebulizer, with 72 +/- 0.73% of this being deposited beyond the vocal cords.

CONCLUSIONS

This technology for categorizing the pulmonary delivery system for lung gene therapy vectors can be adapted for advanced aerosol delivery systems or other vectors.

Advanced Techniques in the Diagnosis and Management of Infectious Pulmonary Diseases in Horses

Techniques for novel approaches to the diagnosis and management of equine pulmonary disease continue to be developed and used in clinical practice. Diagnostic techniques involving immunoassays and nucleic acid-based tests not only decrease the time in which results become available but increase the sensitivity and specificity of test results. These assays do not substitute for careful clinical evaluation but can shorten the time to a confirmed accurate diagnosis, and thus allow for early initiation of therapeutic strategies and prevention protocols. With further understanding of the molecular biology and immunology of equine pulmonary disease, diagnostic and management techniques should become further refined.

Aerosolised antibiotics: a critical appraisal of their use

Aerosolised antimicrobial agents have been used in clinical practice since the 1950s. The main advantage of this route of administration is the targeted drug delivery to the site of infection in the lung. Exploitation of this targeted delivery can yield high concentrations at the site of infection/colonisation while minimising systemic toxicities. It is important to note that the ability of a drug to reach the target area in the lung effectively is dependent on a number of variables, including the nebuliser, patient technique, host anatomy and disease-specific factors. The most convincing data to support the use of aerosolised antimicrobials has been generated with tobramycin solution for inhalation (TOBI, Chiron Corp.) for maintenance treatment in patients with cystic fibrosis. In addition to cystic fibrosis, the use of aerosolised antimicrobials has also been studied for the treatment or prevention of a number of additional disease states including non-cystic fibrosis bronchiectasis, ventilator-associated pneumonia and prophylaxis against pulmonary fungal infections. Key studies evaluating the benefits and shortcomings of aerosolised antimicrobial agents in these areas are reviewed. Although the theory behind aerosolised administration of antibiotics seems to be sound, there are limited data available to support the routine use of this modality. Owing to the gaps still existing in our knowledge base regarding the routine use of aerosolised antibiotics, caution should be exercised when attempting to administer antimicrobials via this route in situations falling outside clearly established indications such as the treatment of patients with cystic fibrosis or Pneumocystis pneumonia.

Nebulized antibiotic therapy: the evidence

The main indications for nebulized antibiotic use are as maintenance therapy for patients with chronic Pseudomonas aeruginosa infection and in treatment protocols aimed at eradicating early P. aeruginosa infection. Daily nebulized antibiotic therapy has been used extensively in Europe for the last 25 years and recently in North America following the introduction of tobramycin solution for inhalation (TSI). The antibiotic is delivered directly to the site of infection, maximizing its efficacy and reducing its potential for toxicity. The efficacy of nebulized antibiotic therapy has been confirmed by meta-analyses of early studies which usually involved only small numbers of patients, and recently by large scale randomized control trials. These studies have shown that regular aerosolized antibiotic treatment results in improved respiratory function, less hospital admissions and respiratory exacerbations, and a significant reduction in the load of P. aeruginosa respiratory tract infection. Concerns about increasing bacterial resistance do not yet seem to have had any clinical impact. Successful eradication of early P. aeruginosa infection has been reported with nebulized colistin (in combination with oral ciprofloxacin), tobramycin and TSI. No advantage has been shown in studies comparing nebulized and intravenous antibiotics versus intravenous antibiotics alone in the treatment of acute respiratory exacerbations. Inhalation of antibiotics may provoke bronchospasm and patients should be assessed before and after treatment prior to continuing long-term therapy at home.

Aminoglycoside antibiotics induce bacterial biofilm formation

Biofilms are adherent aggregates of bacterial cells that form on biotic and abiotic surfaces, including human tissues. Biofilms resist antibiotic treatment and contribute to bacterial persistence in chronic infections. Hence, the elucidation of the mechanisms by which biofilms are formed may assist in the treatment of chronic infections, such as Pseudomonas aeruginosa in the airways of patients with cystic fibrosis. Here we show that subinhibitory concentrations of aminoglycoside antibiotics induce biofilm formation in P. aeruginosa and Escherichia coli. In P. aeruginosa, a gene, which we designated aminoglycoside response regulator (arr), was essential for this induction and contributed to biofilm-specific aminoglycoside resistance. The arr gene is predicted to encode an inner-membrane phosphodiesterase whose substrate is cyclic di-guanosine monophosphate (c-di-GMP)-a bacterial second messenger that regulates cell surface adhesiveness. We found that membranes from arr mutants had diminished c-di-GMP phosphodiesterase activity, and P. aeruginosa cells with a mutation changing a predicted catalytic residue of Arr were defective in their biofilm response to tobramycin. Furthermore, tobramycin-inducible biofilm formation was inhibited by exogenous GTP, which is known to inhibit c-di-GMP phosphodiesterase activity. Our results demonstrate that biofilm formation can be a specific, defensive reaction to the presence of antibiotics, and indicate that the molecular basis of this response includes alterations in the level of c-di-GMP.

Efficacy of aerosolized peroxyacetic acid as a sanitizer of lettuce leaves

Aerosolized sanitizer was investigated as a potential alternative to aqueous and gaseous sanitizers for produce. Peroxyacetic acid was aerosolized (5.42 to 11.42 microm particle diameter) by a commercially available nebulizer into a model cabinet. Iceberg lettuce leaves were inoculated with three strains each of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium and then treated with aerosolized peroxyacetic acid for 10, 30, or 60 min in a model aerosol cabinet at room temperature (22 +/- 2 degrees C). After treatment, surviving healthy and injured bacterial cells were enumerated on appropriate selective agars or using the overlay agar method. Inoculated iceberg lettuce leaves exposed to aerosolized peroxyacetic acid for 10 min exhibited a 0.8-log reduction in E. coli O157:H7, a 0.3-log reduction in Salmonella Typhimurium, and a 2.5-log reduction in L. monocytogenes when compared with the control. After 30 min of treatment, the three pathogens were reduced by 2.2, 3.3, and 2.7 log, and after 60 min, the reductions were 3.4, 4.5, and 3.8 log, respectively. Aerosolization may be a new and convenient method for sanitizing produce for storage or shipping.

In VitroDetermination of the Optimal Particle Size for Nebulized Aerosol Delivery to Infants

We investigated the in vitro influence of breathing patterns on lung dose (LD) and particle size distribution in an infant upper airway cast model in order to determine the optimal particle size for nebulized aerosol delivery to infants. Budesol (nebulizer solution of budesonide) delivery from a perforated vibrating membrane nebulizer (eFlow Baby functional prototype) through an upper airway cast of a nine month old infant (SAINT-model) was measured at a fixed respiratory rate (RR) of 30 breaths per minute (bpm) and a tidal volume (Vt) of 50, 100, and 200 mL, respectively, and at a fixed Vt of 100 mL and a RR of 30, 60, and 78 bpm, respectively. LD expressed as a percentage of the nominal dose (ND; range, 5.8-30.3%) decreased with increasing Vt (p < 0.001) and with increasing RR (p < 0.001). Median mass aerodynamic diameter (MMAD) after passage (range, 2.4-3.4 microm) through the upper airway cast showed a negative correlation with increasing Vt (p < 0.001) and with increasing RR (p = 0.015). Particles available as LD for all simulated breathing pattern showed a particle size distribution with a MMAD of 2.4 microm and a geometric standard deviation (GSD) of 1.56. From our in vitro study, we conclude that the optimal particle size for nebulized aerosols for inhalation therapy for infants should have a MMAD of <2.4 microm.

Significant microbiological effect of inhaled tobramycin in young children with cystic fibrosis

We conducted a double-blind, placebo-controlled, multicenter, randomized trial to test the hypothesis that 300 mg of tobramycin solution for inhalation administered twice daily for 28 days would be safe and result in a profound decrease in Pseudomonas aeruginosa (Pa) density from the lower airway of young children with cystic fibrosis. Ninety-eight subjects were to be randomized; however, the trial was stopped early because of evidence of a significant microbiological treatment effect. Twenty-one children under age 6 years were randomized (8 active; 13 placebo) and underwent bronchoalveolar lavage at baseline and on Day 28. There was a significant difference between treatment groups in the reduction in Pa density; no Pa was detected on Day 28 in 8 of 8 active group patients compared with 1 of 13 placebo group patients. We observed no differences between treatment groups for clinical indices, markers of inflammation, or incidence of adverse events. No abnormalities in serum creatinine or audiometry and no episodes of significant bronchospasm were observed in association with active treatment. We conclude that 28 days of tobramycin solution for inhalation of 300 mg twice daily is safe and effective for significant reduction of lower airway Pa density in young children with cystic fibrosis.

Efficiency of pulmonary administration of tobramycin solution for inhalation in cystic fibrosis using an improved drug delivery system

STUDY OBJECTIVES

To determine whether tobramycin solution for inhalation (TSI) can be administered safely and more efficiently with a new-generation aerosol device, the AeroDose 5.5 RP inhaler (Aerogen; Mountain View, CA) than with the approved PARI LC PLUS nebulizer (PARI Respiratory Equipment; Monterey, CA) with Pulmo-Aide compressor (DeVilbiss Corp; Somerset, PA). Second, we wanted to ascertain which AeroDose-delivered tobramycin dose is equivalent to the standard 300-mg dose administered with the PARI LC PLUS.

DESIGN

Open-label, randomized, multicenter, single-dose, three-period, four-treatment, active- control, crossover trial.

SETTING

Nine US cystic fibrosis (CF) centers.

PATIENTS

Fifty-three patients >or= 12 years of age with a confirmed diagnosis of CF, the ability to expectorate sputum, and FEV(1) of >or= 40% of predicted.

METHODS

Subjects inhaled three single doses of TSI at 1-week intervals, as follows: conventional control treatment, 300 mg via the PARI LC PLUS; and two of three experimental treatments, 30, 60, or 90 mg via the AeroDose. FEV(1) was measured before and after dosing. After each dose, sputum and serum samples were collected at various intervals for 8 h, and urine was collected for 24 h to estimate lung and systemic tobramycin delivery.

RESULTS

There were no significant differences between treatments in the change in FEV(1) 30 min after dosing or in the frequency of adverse events. Sputum and serum levels of tobramycin produced by the AeroDose 90-mg dose treatment approximated those achieved with the PARI LC PLUS 300-mg dose treatment. Nebulization times using the AeroDose inhaler were < 50% those of the PARI LC PLUS.

CONCLUSIONS

Compared with the standard nebulizer, the AeroDose safely achieved an approximately threefold greater efficiency in the delivery of TSI to the lungs in less than half the time.

Nebulized antibiotics in cystic fibrosis

Nebulization is a useful administration route in cystic fibrosis (CF) as it delivers antibiotics directly to the endobronchial site of infection and is associated with decreased toxicity because of limited systemic absorption. It is assumed that the concentration of antibiotics in bronchial secretions should be as high as 10 times the minimum inhibiting concentration to allow penetration of antibiotics into biofilms, suppress inhibitory factors and promote bactericidal effectiveness. However, effective aerosol delivery is compromised by nebulizers with limited capacity to produce particles of a size in the respirable range. Three antibiotics are commonly used for inhalation: tobramycin, amikacin and colistin (colomycin). Placebo-controlled studies evaluating antibiotic aerosol maintenance in stable patients chronically infected with Pseudomonas aeruginosa indicate a significant improvement of lung function and a reduction of the number of hospital admissions for an acute exacerbation of CF. TOBI is a recently marketed preservative- and sulfate-free formula of tobramycin, specially designed for diffusion in the bronchioles and optimal tolerance. A wide-scope study involving 520 patients compared TOBI (300 mg twice daily; n = 258) with placebo (n = 262) for three 28-day cycles with each cycle separated by a 28-day period of no treatment. Respiratory function was significantly improved as early as in the second week and remained so for the rest of the trial even during periods without aerosol treatment. There was also a parallel decrease in the relative risk of hospitalization, the number of days of hospitalization and the number of days on intravenous antipyocyanic treatment. Toxicity studies carried out so far have shown no renal or ototoxicity with nebulized tobramycin. Introduction or selection of resistant bacteria is relatively rare but remains a matter of concern. Aerosol maintenance treatment with an appropriate antibiotic in a high enough dosage can be recommended for patients with CF who are chronically infected with P. aeruginosa.

Pharmaceutical and biotechnological aerosols for cystic fibrosis therapy

This review addresses different aerosol therapies used to treat the underlying cause and symptoms of cystic fibrosis (CF) during the past two decades. A summary of the current methods of aerosol delivery and suggestions that may improve the efficacy of the current treatments are provided.

Aerosols in bronchiolitis

Bronchiolitis is a common illness of the lower respiratory tract affecting infants that has considerable short and long-term morbidity and occasional mortality. It is the commonest cause of hospitalization for respiratory infection in early childhood, and the seasonal nature of the illness places considerable strain on health care resources during the bronchiolitis season. The youngest infants and those with preexisting cardiorespiratory disease are particularly at risk of severe illness. The treatment of infants with bronchiolitis is largely supportive. There are no therapies that have been proven to reduce the length of the hospitalization or intensive care stay. This paper will review the clinical course of bronchiolitis and discuss the aerosolized therapies that have been proposed for its treatment.

Effects of inhaled gentamicin prophylaxis on acquisition of Pseudomonas aeruginosa in children with cystic fibrosis: a pilot study

Inhaled antibiotics are an established treatment for chronic Pseudomonas aeruginosa (PA) infection in patients with cystic fibrosis (CF). However, inhaled antibiotics might also have prophylactic potential to delay acquisition of PA in early stages of the disease. From 1986-1999, all CF patients at this center who experienced defined risk situations for acquisition of PA (28 patients) received inhaled gentamicin (80 mg BID for those < 12 months; 120 mg BID for those > 12 months) for a minimum of 3 years. Twelve patients had repeated risk situations and continued this prophylaxis without interruption during the entire study period (group 1). In the remaining 16 patients, inhaled antibiotics were discontinued at various times for a variety of reasons (group 2). None of the patients in group 1, but 7 in group 2, became chronically infected with PA (P = 0.01). Lung function and chest X-ray scores were significantly worse in those 7 infected patients, when compared to the noninfected ones in both groups. This suggests that long-term-prophylaxis with inhaled gentamicin can effectively delay acquisition of PA and decrease disease progression in children with CF.

Pulmonary administration of perfluorodecaline- gentamicin and perfluorodecaline- vancomycin emulsions

The aim of this study was to examine pharmacokinetics and pulmonary antibiotic tissue concentrations (PATC) of gentamicin and vancomycin after intrapulmonary administration of a perfluorodecaline (PFD)-gentamicin and a PFD-vancomycin emulsion during partial liquid ventilation (PLV). PLV was initiated in 19 healthy rabbits and 18 surfactant-depleted rabbits. The animals were randomized to receive either 5 mg/kg gentamicin and 15 mg/kg vancomycin intravenously, or 5 mg/kg gentamicin intrapulmonary, or 15 mg/kg vancomycin intrapulmonary. Antibiotic plasma levels were measured after 15, 30, 45, and 60 min, and hourly thereafter. After 5 h animals were sacrificed and lungs were removed to evaluate PATC and histology. PATC were significantly higher after intrapulmonary administration of both gentamicin and vancomycin. In healthy rabbits, peak plasma concentrations were lower and 5 h plasma concentrations were higher after intrapulmonary administration, whereas plasma concentrations were not different in surfactant-depleted rabbits. There were no differences in lung histology, hemodynamics, lung mechanics, or gas exchange between the treatment groups. We conclude that during PLV, higher PATC can be achieved after intrapulmonary administration of PFD-antibiotic emulsions compared with intravenous administration of the same dose without apparent short-term adverse effects. We speculate that intrapulmonary antibiotic administration during PLV may be beneficial in treating severe pneumonia.

Serum and lower respiratory tract drug concentrations after tobramycin inhalation in young children with cystic fibrosis

OBJECTIVES

To assess the serum and lower respiratory tract tobramycin concentrations (C(T)) produced by a single dose of tobramycin for inhalation delivered by a nebulizer and a compressor in patients with cystic fibrosis (CF) 6 months to 6 years of age.

STUDY DESIGN

We performed a dose escalation study of serum C(T) measured before and 0.5, 1, 2, and 4 hours after a single dose of inhaled tobramycin, either 180 mg (10 patients) or 300 mg (19 patients). In a separate group of 12 patients, epithelial lining fluid (ELF) C(T) was measured by bronchoalveolar lavage 30 to 45 minutes after a 300-mg dose.

RESULTS

A 180-mg dose of inhaled tobramycin produced a mean peak serum C(T) of 0.5 microg/mL (SD 0.4; range, <0.2 to 1.4 microg/mL). A 300-mg dose produced a mean peak serum C(T) of 0.6 microg/mL (SD 0.5; range, <0.2 to 1.2 microg/mL). These peak values are well below the accepted maximum trough concentration with parenteral dosing (2 microg/mL). The target ELF C(T) was 20 microg/mL, 10-fold greater than the minimal inhibitory concentration for most Pseudomonas aeruginosa isolates from very young patients with CF (2 microg/mL). Mean ELF C(T) was 90 microg/mL (SD 54; range, 16 to 204 microg/mL) and exceeded the target concentration in 11 patients.

CONCLUSION

In patients with CF ages 6 months to 6 years, a single 300-mg dose of inhaled tobramycin appears to produce safe peak serum concentrations and drug concentrations in the bactericidal range in the lower respiratory tract.

Accounting for radioactivity before and after nebulization of tobramycin to insure accuracy of quantification of lung deposition

The ability to predict drug deposition of inhaled drugs used in cystic fibrosis (CF) is important if there is a need to target specific doses of drug to the lungs of individual patients. The gold standard of measuring pulmonary deposition is the quantification of an aerosolized radiolabel either mixed with the drug solution or tagged directly to the compound of interest. Accuracy of the quantification could be assured if there is agreement between the amount of radioactivity before and after administration. Before administration, the radiolabel is concentrated in the well of the nebulizer, whereas after administration, it is distributed throughout the nebulizer, the expiratory filter and connectors, and the upper airway, stomach, trachea, and lung. Not only is the geometry of the distribution that is presented to the gamma camera different, but there are different attenuation factors for the various body tissues. The primary aim of this study was to evaluate the accuracy of the quantification of deposition. Secondary goals were to compare in vitro nebulizer performance with that measured in vivo during the deposition study. Eighty milligrams of tobramycin and technetium bound to human serum albumin was administered to 10 normal adults using a Pari LC Jet Plus (Pari Respiratory Equipment, Inc., Richmond, VA) breath-enhanced nebulizer. Techniques were developed that allowed for the accounting of 99 +/- 2% of the initial radioactivity. The fraction of the rate of lung deposition to total body deposition was the in vivo respirable fraction (0.62 +/- 0.07), which closely agreed with in vitro measurements of respirable fraction (0.62 +/- 0.04). Drug output measured from the change in weight and concentration in the nebulizer systematically overestimated drug output measured by the deposition study. The results indicate that 11.8 of the initial 80 mg would be deposited in the lungs. This technique could be adapted to accurately quantify the amount of deposition on any inhaled therapeutic agent, but caution must be used when extrapolating performance of a nebulizer on the bench to expected deposition in patients.

Effect of size and disease on estimated deposition of drugs administered using jet nebulization in children with cystic fibrosis

STUDY OBJECTIVES

To develop a model that quantified the nebulizer output that was inhaled by subjects with cystic fibrosis (CF) in order to predict the amount of drug likely to enter the upper airway contained in particles small enough to be deposited in the lower respiratory tract of individual patients.

DESIGN

Forty-three patients (age, 6 to 18 years) with CF, with FEV(1) of 26 to 124% of predicted, breathed through a nebulizer circuit with a pneumotachograph in place at the distal end. Algorithms were developed from the measured flows through the pneumotachograph, allowing partitioning of inspiration into undiluted aerosol and fresh gas. In order to validate the algorithms, argon was added to the nebulizing gas flow and then its concentration was analyzed at the mouth by mass spectrometry.

RESULTS

Predictions of the concentration of argon at the mouth were concordant with that measured by mass spectrometry, thus validating the model. Combining data from the model with in vitro nebulizer performance data, predictions for estimates for lung deposition for individuals were possible. Total estimate was independent of patient size or FEV(1). The respiratory duty cycle was 0.44 +/- 0.05 (mean +/- SD) and correlated (r = 0.91, p < 0.001) with estimated deposition and minute ventilation (r = 0.60, p < 0.01). However, when expressed in milligrams per kilogram of body weight, the estimated deposition in smaller children was fourfold higher than in larger children.

CONCLUSIONS

If the effect of patient size and pattern of breathing on estimated drug deposition are not considered when prescribing drugs given by nebulization, the result may be overdosing younger children, underdosing older children, or both.

Aerosolized antimicrobial therapy in acutely ill patients

Recent data are sparking renewed interest in therapy with aerosolized antimicrobials in critically ill patients as well as other populations such as those with neutropenia, human immunodeficiency virus infection, and cystic fibrosis. Pneumonia is a common complication in these patients and is associated with substantial morbidity and increased mortality. Clinical trials evaluated aerosolized antimicrobials for the prevention and treatment of pneumonia in hospitalized patients. In addition, factors that affect the pulmonary deposition of aerosolized drugs in mechanically ventilated patients were identified.

Can tobramycin inhalation be improved with a jet nebulizer?

Data on the pharmacokinetics of antibiotics after inhalation are limited. The aim of this pilot study was to assess the pharmacokinetics of tobramycin under optimalized and standardized aerosol circumstances and, furthermore, to be able to consider possible treatment of exacerbations with inhalation therapy. Six patients were studied after inhalation of 600 mg tobramycin. A jet nebulizer loaded with a 10% solution of tobramycin in water was used. The percentage of the dose that was systemically absorbed ranged from 1.0% to 16.6%. The maximum serum levels of tobramycin ranged from 0.77 mg/L to 3.63 mg/L (mean 1.70 +/- 1.01). The pharmacokinetic data were best described by a two-compartment model. Compared to intravenous administration, the long terminal half-life (mean 9.47 h +/- 3.28 h) could be explained by the slow absorption of tobramycin from the site of administration (flip-flop model). Despite standardized aerosol conditions, considerable interpatient variability was observed. However, the relatively low serum levels allow a further increase of the dose.

Improvement of nebulised antibiotic delivery in cystic fibrosis

AIM

To investigate deposition patterns and to assess the delivery rate of two nebuliser systems in children with cystic fibrosis (CF).

METHODS

Thirty three children with CF on regular treatment with nebulised antibiotics had radioisotope scans performed using technetium-99m labelled aerosol antibiotic generated by a Ventstream nebuliser (median mass diameter (MMD), 3.3 microm; delivery rate, 0. 075 ml/min) under conditions similar to their routine home practice. The inhomogeneity of the images was scored on a 1-10 rating scale (a low score indicating even distribution of the antibiotic), and stomach deposition was measured as a percentage of overall deposition. Twenty patients had a repeat scan using an Optimist nebuliser (MMD, 1.8 microm; delivery rate, 0.02 ml/min).

RESULTS

The mean inhomogeneity scores were 5.4 in the Ventstream group and 3. 5 in the Optimist group. Mean stomach deposition was 17.3% in the 33 patients using the Ventstream nebuliser. There was an inverse relation between height and stomach deposition (r = 0.69). In the 20 patients who had both nebulisers, the mean percentages of stomach deposition for the Ventstream and Optimist nebulisers were 11.8% and 1.6%, respectively. The Ventstream nebuliser delivered antibiotic at an average 2.8 times faster rate than the Optimist nebuliser.

IMPLICATIONS

A smaller particle size results in a more homogenous distribution of the antibiotic in the lungs with decreased stomach deposition. This should not be seen as a recommendation to use the Optimist nebuliser because more antibiotic was delivered to most parts of the lung with the Ventstream because of its increased delivery rate.

Lung clearance of intratracheally instilled 99mTc-tobramycin using pulmonary surfactant as vehicle

1. The use of pulmonary exogenous surfactant as a vehicle for intratracheally administered antibiotics to improve local antimicrobial therapy has been proposed. The present study investigated lung clearance rates in the rat of intratracheally instilled technetium labelled tobramycin with and without the addition of surfactant to the antibiotic solution. 2. The influence of surfactant on 99mTc-tobramycin lung clearance rates was studied dynamically with a gamma-camera in anaesthetized spontaneously breathing animals and in mechanically ventilated animals. 3. The results show that instillation of 99mTc-tobramycin with use of surfactant as vehicle significantly increases 99mTc-tobramycin lung clearance compared to instillation of 99mTc-tobramycin solution alone (P=0.006 between the two spontaneously breathing groups of animals and P=0.02 between the two ventilated groups of animals, ANOVA for repeated time measurements). The half life (t1/2) of composite clearance curves in spontaneous breathing animals was 147 min for animals receiving 99mTc-tobramycin versus 61 min for animals receiving 99mTc-tobramycin with surfactant. In mechanically ventilated animals this was 163 min versus 51 min, respectively. 4. It is concluded that exogenous surfactant, used as vehicle for intratracheally instilled 99mTc-tobramycin, increases lung clearance rate of 99mTc-tobramycin in rats.