Electrohydrodynamic Comminution: A Novel Technique for the Aerosolisation of Plasmid DNA

Purpose Naked plasmid DNA (pDNA) is a potential gene transfer agent for lung gene therapies but cannot be aerosolised without degradation using conventional nebulisation devices. This study investigated the viability of an alternative nebulisation technique, electrohydrodynamic (EHD) comminution for the aerosol delivery of naked DNA in vivo.Methods Naked pDNA was aerosolised using jet and ultrasonic nebulisers, and by EHD comminution. Degradation associated with the aerosolisation process was investigated using gel electrophoresis and by transfection studies in cell culture. Optimised formulations for EHD aerosolisation of pDNA were developed and in vivo deposition and reporter gene expression were investigated in mice.Results Unlike conventional nebulisation devices, EHD comminution of plasmids up to 15 kb in size resulted in no detectable pDNA degradation. EHD formulations containing up to 1 mg/ml pDNA were developed and shown to produce monodisperse aerosols suitable for targeted lung delivery in humans. Aerosolisation studies in vivo demonstrated detectable levels of pDNA deposition and measurable luciferase reporter gene expression in the lungs of exposed mice.Conclusions This study demonstrates for the first time that respirable aerosols of naked pDNA can be generated without plasmid degradation and that EHD comminution is an appropriate technique for the aerosolisation of delicate gene transfer agents.     

Influence of formulation on jet nebulisation quality of alpha 1 protease inhibitor

As foam appears during solution constitution and nebulisation of alpha 1 protease inhibitor (alpha 1 PI), we selected in a previous work, antifoams likely to be associated with an alpha 1 PI solution to be nebulised: span 65 at a 0.025% concentration and cetyl alcohol at a 0.05% concentration associated with tyloxapol at 0.025% concentration. The purpose of this study was, on the one hand to study the influence of the formulation on nebulisation quality by relating physicochemical properties and nebulisation capacity, and on the other hand, to define the alpha 1 PI that will be retained for a clinical study. The properties of the different alpha 1 PI formulations are compared: surface tension, viscosity, time required to constitute the protein solution and pH. Nebulisation quality is evaluated under different operating conditions by measuring the droplet size, the quantity of alpha 1 PI nebulised, nebulisation time and the quantity of alpha 1 PI likely to reach the lungs which was subjected to statistical analysis. The statistical analysis of results indicates that the addition of the cetyl alcohol/tyloxapol mixture improves nebulisation effectiveness by significantly increasing the quantity of drug nebulised and therefore the quantity of alpha PI likely to reach the lungs. It is this formulation that will be retained for clinical trials. We check that the nebuliser and operating conditions influence all the parameters, that is to say the respirable fraction, the quantity nebulised and the nebulisation time. Although there is no interaction between the nebuliser and the formulation, nebulisation quality is the combined result of the formulation, the nebuliser and the operating conditions.     

Influence of the technological parameters of ultrasonic nebulisation on the nebulisation quality of alpha1 protease inhibitor (alpha1PI).

The principle of an ultrasonic nebuliser is based on the vibrations of a piezo-electric crystal driven by an alternating electrical field. These periodical vibrations are characterised by their frequency, their amplitude and their intensity which corresponds to the energy transmitted per surface unit. When the vibration intensity is sufficient, cavitation appears and generates droplets. Ventilation enables an airflow to cross the nebuliser and to expulse the aerosol droplets. For a given nebuliser, the vibration frequency of the piezo-electric crystal is fixed and is often in the range of 1-2.5 MHz. In most cases, an adjustment in vibration intensity is possible by modifying vibration amplitude. The ventilation level is adjustable. The influence of these two parameters on the efficiency of ultrasonic nebulisation is studied. The study was carried out with a protein solution that had to be administered into the lungs. The solution used presented a viscosity of 1.25 mPa and a surface tension of 53 mN/m. The integrity of the protein was checked which was submitted to different vibration conditions. Nebulisation efficiency was evaluated by determining droplet size, the percentage of drug nebulised and nebulisation time. An increase in vibration intensity does not modify the size of droplets emitted, but decreases nebulisation time and raises the quantity of protein nebulised, thus improving performance. On the other hand, an increase in ventilation increases the size of droplets emitted, decreases nebulisation time and the quantity of protein nebulised because more drug is lost on the walls of the nebuliser. High intensity associated with low ventilation favours drug delivery deep into the lungs.     

Enhanced delivery of nebulised salbutamol during non-invasive ventilation

Non-invasive ventilation (NIV) is used to treat acute respiratory failure. Nebulised drugs can be delivered concurrently with NIV or during breaks from ventilatory support. We hypothesised that the amount of nebulised salbutamol inhaled when delivered via bi-level ventilation would be no different to the amount available directly from the same nebuliser. A standard bi-level ventilation circuit was attached to a lung model simulating adult respiration. Drug delivery was compared when salbutamol (5 mg) was nebulised at different positions in the circuit and separately, with no ventilator. The amount of salbutamol contained in various particle size fractions was also determined. Nebuliser position within the NIV circuit was critically important for drug delivery. Optimal delivery of salbutamol occurred with the expiration port between the facemask and nebuliser (647+/-67 micro g). This was significantly better than nebulisation without the ventilator (424+/-61 micro g; P < 0.01). Delivery when the nebuliser was positioned between the facemask and expiration port was 544+/-85 micro g. The amount of salbutamol contained in particles < 5 micro m was significantly increased when the nebuliser was used in conjunction with bi-level ventilation (576+/-60 micro g vs 300+/-43 micro g, P < 0.001). We conclude that nebulised bronchodilator therapy, using a Cirrus jet nebuliser, during bi-level ventilation increases respirable particles likely to be inhaled when the nebuliser is optimally positioned within the circuit.     

Assessment of antibiotic aerosol generation using commercial jet nebulizers.

The performance of 14 commercial jet nebulisers has been assessed; Unineb, Suremist (Unimed (UK) Ltd), Micro-Cirrus (Intersurgical Ltd), Pulmo-Neb (DeVilbiss Health Care UK Ltd), Side-Stream (Medic-Aid Ltd), Micro-Neb III (Lifecare Ltd), RespirGard (Marquest Medical Products Inc), Aeromist, Venticaire (S and W Vickers Ltd), Up-Draft II, Ava-Neb, Up-Draft (Hudson Respiratory Care Inc), Bennett/Twin, Raindrop (Puritan-Bennett Corporation). The units were operated with a high flow compressor (Maxi III, Medix Ltd) at 101/min. Performance was assessed by measuring the fraction of the initial mass of drug released as an aerosol and nebulisation time for initial drug volume of 2-6mls, and the mass median diameter and mass fraction of the aerosol in particles < 5.17 microns diameter. The Side-Stream nebuliser gave the best performance, although incorporation of a filter to trap exhaled antibiotic may prove difficult. The Micro-Cirrus generated a particularly fine aerosol. The Raindrop nebuliser performed well, while the Up-Draft II nebulised efficiently but was associated with extended nebulisation times which may limit its utility.     

Mannitol delivery by vibrating mesh nebulisation for enhancing mucociliary clearance

Mucociliary clearance is compromised by airway surface liquid dehydration in respiratory disease states such as cystic fibrosis. Rehydration by hyperosmolar agents such as nebulised hypertonic saline and dry powder mannitol has demonstrated in vivo safety and efficacy for restoring mucociliary function. Mannitol, delivered as a nebulised formulation for this purpose, has not been investigated as yet. The current study examines the feasibility of delivering such a formulation using recent vibrating mesh technology. Nebulisation was conducted using an Aeroneb Go(TM) vibrating mesh nebuliser, and aerosol size was assessed by laser diffraction. Cascade impaction coupled with mass assay by high-performance liquid chromatography was used to confirm fluid uniformity and correlation with laser diffraction sizing. The following nebuliser formulations were prepared and aerosolised: deionised water, mannitol (150 mg/mL) aqueous solution, sodium chloride aqueous solution [0.2%, 1%, 3%, 5%, 7% (w/v)] and mannitol (150 mg/mL) in sodium chloride solution [0.2%, 1%, 3%, 7% (w/v)]. Mannitol aqueous solution was poorly nebulised, resulting in lengthy treatment times and large median droplet size. Addition of sodium chloride drastically improved nebuliser performance and aerosol characteristics. In vivo studies are necessary to confirm efficacy of nebulised mannitol. If substantiated, it could provide a pleasant-tasting alternative mucoactive agent with prolonged therapeutic action.     

An assessment of jet and ultrasonic nebulisers for the delivery of lactate dehydrogenase solutions

The aim of this study was to investigate the suitability of commercial jet and ultrasonic nebulisers for effective delivery of the model hydrophilic protein lactate dehydrogenase (LDH). Two jet nebulisers (Pari LC Plus and Pari LC Star) and two ultrasonic nebulisers (Sonix 2000 and Omron U1) were used to nebulise LDH solutions and the effects on protein activity and protein concentration determined. The size distribution of the aerosols produced, measured by laser diffraction analysis, temperature changes during nebulisation, the time to atomise a 5 ml dose volume and the mass output of the four nebulisers were compared. A twin impinger (TI) was used to collect the nebulised protein, which was assayed for total and active protein content. There was a large variation in the median size and size distribution of the aerosols produced by each of the nebulisers from LDH and S?rensen's modified phosphate buffer, and in the time taken to reach the sputtering phase of aerosolisation. During use, the concentration of LDH increased in the Omron U1 nebuliser, but did not change significantly in the others. The temperature of the protein solution decreased by approximately 8 degrees C during jet nebulisation but increased by 3 and 10 degrees C in the Omron U1 and Sonix 2000 nebulisers, respectively. Denaturation of LDH within the nebuliser reservoir, occurred in the order Sonix>Pari LC Plus>Pari LC Star>Omron U1, whilst the deposition of active and total protein within the stages and throat of the TI was a function of the particle size of the aerosols generated and the specific device used.     

In Vitro Reporter Gene Transfection via Plasmid DNA Delivered by Metered Dose Inhaler

Aerosolised DNA administration could potentially advance the treatment of inheritable lung diseases, lung malignancies and provide genetic immunisation against infection. Jet nebulisation, the current standard for introducing DNA formulations into the lung, is inherently inefficient. Pressurised metered dose inhalers (pMDIs) offer a potentially more efficacious and convenient alternative, especially for repeat administration. We aim to modify a novel low-energy nanotechnology process to prepare surfactant-coated pDNA nanoparticles for pulmonary gene delivery via a pMDI. Water-in-oil microemulsions containing green fluorescent protein reporter plasmid were snap-frozen and lyophilised. Lyophilised pDNA, in some cases following a surfactant wash, was incorporated into pMDIs with hydrofluoroalkane 134a (HFA134a) propellant and ethanol as cosolvent. To assess biological functionality, A549 human lung epithelial cells were exposed to aerosolised pDNA particles in the presence of dioleoyl-trimethylammonium propane (DOTAP). Transfection studies demonstrated that pDNA biological functionality was maintained following aerosolisation. In vitro toxicity assays (MTT) showed no significant cell viability loss following aerosolised pDNA treatment. We have demonstrated that pDNA particles can be incorporated into an HFA134a formulation and aerosolised using a standard valve and actuator. Particles prepared by this novel process have potential for stable and efficient delivery of pDNA to the lower respiratory tract via standard pMDI technology.     

Cooling the NGI - an approach to size a nebulised aerosol more accurately

The European Pharmaceutical Aerosol Group (EPAG) has undertaken investigations with the aim of developing robust methods for the droplet size analysis of nebuliser-produced aerosols in support of the proposed European Pharmacopeia general chapter 2.9.44 covering preparations for nebulisation. A multi-centre study was designed to investigate the effects of cooling the Next Generation pharmaceutical Impactor (NGI) before sample collection, as a means of reducing bias and variability caused by heat transfer-related evaporation. Droplets containing salbutamol were sized from 3 different nebulisers chosen to offer fundamentally different modes of aerosol generation: AeroNeb Go, a vibrating mesh nebuliser; PARI LC Plus, a breath-enhanced jet nebuliser; and MistyMax, a constant-output jet nebuliser. Each laboratory undertook determinations at ambient temperature, using an NGI pre-cooled in a refrigerator (5 degrees C for at least 90 min). The corresponding measurements were made using an ambient NGI as a benchmark. Salbutamol solution 5 mg/2 ml (Teva, Runcorn, UK) was used throughout the study. Analysis of individual and pooled results from 5 of the participants showed a similar trend insofar as the cooled NGI yielded a coarser nebulised aerosol than that obtained by the ambient NGI. Mass Median Aerodynamic Diameter (MMAD) was on average reduced by 9.5-21.9 % and the Fine Droplet Fraction < 5 microm (FDF) increased on average by 5.5-17.4 % for all the nebuliser designs when comparing ambient to cooled NGI. Despite the more laborious procedure of cooling the NGI, variability in data was generally similar to that obtained with the ambient NGI. We conclude that it is beneficial to cool the NGI when sizing nebulised aerosol. Furthermore, occasional findings during this study revealed a build-up of solute deposits within the interior of the NGI, and a more rigorous impactor cleaning/drying procedure is therefore recommended.     

The choice of a compressor for the aerosolisation of tobramycin (TOBI) with the PARI LC PLUS reusable nebuliser

The performance of five different compressors (CR60), Porta-Neb, Pulmo-Aide, TurboBoy and Freeway Freedom) was studied in combination with the widely recommended PARI LC PLUS nebuliser for the aerosolisation of a marketed tobramycin solution (TOBI). The droplet size distribution of the generated aerosol was measured with laser diffraction technique at stationary inspiratory flow rates through the nebuliser cup of 20, 30 and 40l N/min. The different compressors showed a distinct difference in droplet size distribution of the aerosol and nebulisation time till dry running. The finest droplets with a volume (equals mass) median diameter (mmd) of 1.84 microm (which was the same at all flow rates), as well as the narrowest size distribution were obtained with a CR60. The Freeway Freedom generated the largest droplets: mmd ranged between 2.63 and 3.72 microm depending on the inspiratory flow rate. The aerosol produced with this compressor also had the widest size distribution. The differences between the compressors could be explained with differences in the jet flow. A higher jet flow resulted in finer droplets, less dependence on the inspiratory flow rate and a shorter time till dry running. Thus, to obtain the required fineness of the aerosol for peripheral airway deposition of the tobramycin, independent of the inspiratory flow rate, the use of the CR60 compressor is preferred over the use of Porta-Neb, Pulmo-Aide, TurboBoy and Freeway Freedom (in order of decreasing preference). Finally, it was found that careful cleaning with warm water and liquid soap of the nebuliser cup is essential to obtain adequate performance of the LC PLUS.     

In vivo studies of dialkynoyl analogues of DOTAP demonstrate improved gene transfer efficiency of cationic liposomes in mouse lung

A novel set of dialkynoyl analogues of the cationic, gene delivery lipid DOTAP (1) was synthesized. Structure-activity studies demonstrate that replacement of the cis-double bonds of DOTAP with triple bonds in varying positions alters both the physical properties of the resultant cationic liposome-DNA complexes and their biological functionalities, both in vitro and in vivo. Particularly, in vivo studies demonstrate that pDNA transfection of mouse lung endothelial cells with lead analogue DS(14-yne)TAP (4):cholesterol lipoplexes exhibits double the transfection level with less associated toxicity relative to the well-established DOTAP:cholesterol system. In fact, 4:cholesterol delivers up to 3 times the dose of pDNA in mice than can be tolerated by DOTAP, leading to nearly 3 times greater marker-gene expression. X-ray diffraction studies suggest that lipoplexes containing analogue 4 display increased stability at physiological temperatures. Our results thus suggest that analogue 4 is a potentially strong candidate for the gene therapy of lung tumors.     

Nebulised gentamicin-suitable for childhood bronchiectasis

Nebulised antibiotic therapy is an established, safe and effective therapy for cystic fibrosis with chronic pseudomonas infection resulting in improved pulmonary function and reduced hospitalisation. Despite similar respiratory disease, this therapy has not been evaluated in children with non cystic fibrosis bronchiectasis. This study evaluates the suitability of a gentamicin solution and nebuliser combination for use in this population. MATERIALS AND METHODS: Four millilitres of gentamicin (80 mg) in saline delivered by a PARI LC plus nebuliser and PARI Turboboy N compressor was used. The pH, osmolarity, chloride concentration and aerosol particle size was determined. Ten children with non cystic fibrosis bronchiectasis received nebulised antibiotic and had peak gentamicin concentrations measured in sputum and serum. Pulmonary function was measured pre and post nebulisation. RESULTS: The solution had an osmolarity of 199 mOsm/l, pH of 4.1, chloride concentration of 75 mmol/l and the aerosol a mass median aerodynamic diameter of 3.3 microm. Nebulisation was well tolerated, with no significant change in FEV1. Peak serum levels were at the threshold of detectability (0.3 mg/l). Sputum concentrations had a mean of 624 mg/g and lower 95th confidence interval 25 times the minimum inhibitory concentration for the predominant infecting organism, Haemophilus influenzae. CONCLUSION: Nebulisation of 80 mg of gentamicin in saline achieved bactericidal concentrations in sputum, was well tolerated and had negligible systemic absorption making it a suitable choice for this population.     

A spermine-deoxycholic acid conjugate based lipid as a transfecting agent

Deoxycholic acid-spermine conjugate (DAS), which is composed of natural components (deoxycholic acid and spermine), was incorporated in liposomes and evaluated for its interaction with plasmid DNA (pDNA) and in vitro transfection efficiency. Electromicrographs demonstrated that DAS-pDNA complexes are spherical, compact and electronically dense compared to the toroidal shapes formed by the monovalent lipid 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) and pDNA. In comparison to the singly charged, non-cholesterol based lipid (DOTAP), the multivalent lipid DAS had similar transfection efficiency in two cell lines. The monovalent sterol, deoxycholic acid propyldiamine conjugate (DAP) was not effective as a transfecting agent. This suggests that multivalent facial amphiphiles such as DAS may serve as excellent candidates for non-viral gene transfer and warrant further study.     

Plasma concentrations of disodium cromoglycate after various inhalation methods in healthy subjects

AIMS: To compare the plasma concentrations of disodium cromoglycate (DSCG) following various inhalation procedures in healthy volunteers. METHODS: Nine healthy subjects inhaled 2 mg of aerosol, 20 mg of nebuliser solution only, 20 mg of nebuliser solution mixed with isotonic saline, or 20 mg of nebuliser solution mixed with saline and procaterol, a beta2-adenoceptor agonist, on separate occasions 2-3 weeks apart. Plasma concentrations of DSCG were determined by high-performance liquid chromatography (h.p.l.c.). RESULTS: The peak plasma concentrations of DSCG were 1.5+/-0.7 (range 0.4-2.4) ng ml-1 in the aerosol group, 8.8+/-6.2 (range 5.3-19.9) ng ml-1 in the nebuliser solution only group, 17.2+/-16.3 (range 5.0-38.6) ng ml-1 in the nebuliser solution plus isotonic saline group, and 24.5+/-11. 9 (range 10.2-44.9) ng ml-1 in the nebuliser solution plus saline and procaterol group. Thus subjects who used the nebuliser had markedly higher plasma concentrations of DSCG than subjects who used the aerosol inhaler. CONCLUSIONS: These findings may have important implications for the evaluation of inhalation treatment with DSCG for bronchial asthma.     

The use of water as a diluent for bronchodilator nebuliser solutions

Inhalation of nebulised water can provoke bronchoconstriction in asthmatic patients. In the first part of this study, a community survey identified that about 20% of patients with home nebulisers currently use water as a diluent. In the second part of this study, the airways effect of the use of water as a diluent for nebulised beta agonist was investigated. Nineteen asthmatic subjects were administered nebulised 2.5 mg salbutamol, diluted with either 2 mL water or physiological saline, and forced expiratory volume in one second (FEV1) was measured at baseline and at regular intervals for 45 minutes after nebulisation. Although there was a trend towards a reduced bronchodilator response with water as diluent, the differences between the two diluents were not significantly different. Paradoxical bronchoconstriction was not observed when salbutamol was diluted with water. We conclude that the common practice of diluting bronchodilator nebuliser solution with water does not result in a significant reduction in the overall bronchodilator response.     

Factors determining the superior performance of lipid/DNA/protammine nanoparticles over lipoplexes

The utility of using a protammine/DNA complex coated with a lipid envelope made of cationic 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) for transfecting CHO (Chinese hamster ovary cells), HEK293 (human embryonic kidney cells), NIH 3T3 (mouse embryonal cells), and A17 (murine cancer cells) cells was examined. The widely used DOTAP/DNA lipoplex was employed as a reference. In all the tested cell lines lipid/protamine/DNA (LPD) nanoparticles were more efficient in transfecting cells than lipoplexes even though the lipid composition of the lipid envelope was the same in both devices. Physical-chemical properties were found to control the ability of nanocarriers to release DNA upon interaction with cellular membranes. LPD complexes easily release their DNA payload, while lipoplexes remain largely intact and accumulate at the cell nucleus. Collectively, these data explain why LPD nanoparticles often exhibit superior performances compared to lipoplexes in trasfecting cells and represent a promising class of nanocarriers for gene delivery.     

In vitro characterization and transfection of IL-2 gene complexes

BACKGROUND: Interleukin-2 used in the treatment of malignant tumors has an anti-tumor efficacy. In this study, we have studied in vitro characterization and transfection efficiency of a plasmid encoding hIL-2, pCXWN-hIL-2, complexed to chitosan, polyethylenimine or DOTAP with varying ratios. METHODS: Plasmid DNA was amplified in Escherichia coli DH5alpha and isolated by alkali lysis method. The pDNA/chitosan, pDNA/PEI or pDNA/DOTAP complexes were analyzed by agarose gel electrophoresis for complex formation and by ESEM image analysis system for the morphology and DNA/medium relationship of complexes. DNase stability, the particle size and zeta potential values of complexes were determined. Transfection efficiencies of resulting complexes in two different cell lines were assayed by ELISA method. RESULTS: Conclusively, a transfection activity was observed in both cell lines (HeLa and Swiss3T3) with the order of pDNA/DOTAP>pDNA/PEI>pDNA/chitosan complexes. We have observed that the transfection efficiency was higher in HeLa cell line compared to Swiss3T3 cell line. CONCLUSION: The physicochemical studies like stability, particle size and zeta potential, showed a relationship between the properties of a complex and its transfection efficiency.     

An in vitro investigation into the effect of glycosaminoglycans on the skin partitioning and deposition of NSAIDs

Beclomethasone dipropionate (BDP) liposomes were prepared from various lipids, dilauroyl phosphatidylcholine (DLPC), dimyristoyl phosphatidylcholine (DMPC), dipalmitoyl phosphatidylcholine (DPPC), and hydrogenated soybean phosphatidylcholine (Epikuron 200 SH). A lipid with a low transition temperature (T(m)) (DLPC) incorporated a higher amount of BDP than lipid with a high T(m). The nebulisation of rehydrated freeze-dried BDP liposomes was carried out using a Pari LC Plus nebuliser and the generated aerosol characterised by an Andersen Cascade Impactor operated at 28.3 l/min. The rehydrated BDP-DLPC liposomes showed a higher output (78.3%) and a higher fine particle fraction (FPF) (75.0%) and smaller mass median aerodynamic diameter (MMAD) (3.31 microm) than the other rehydrated liposome preparations. Liposomes containing lipid with a high T(m) (DPPC and Epikuron) underwent aggregation during nebulisation. This was shown by the large increase in size of the DPPC liposomes from 15.78 to 47.51 microm and the Epikuron liposomes from 5.84 to 46.70 microm.     

Tobramycin for nebulisation: new formulation. A high price for a small improvement in formulation

(1) In patients with cystic fibrosis, chronic bronchial infection with Pseudomonas aeruginosa is a major factor in the development of chronic respiratory failure and premature death. (2) Over the last two decades, such patients have commonly received long-term treatment with antibiotic aerosols (mainly tobramycin or colistin, in off-licence uses). (3) Tobramycin solution for nebulisation is the first antibiotic preparation to be licensed in the EU for this indication. (4) Comparative evaluation of antibiotic aerosol therapy for chronic bronchial infections due to P. aeruginosa includes two large trials of nebulised tobramycin. (5) A combined analysis of these two placebo-controlled trials, both lasting 20 weeks, showed that tobramycin aerosol delayed the deterioration of respiratory function and reduced the number of hospitalisations. However, an increase in P. aeruginosa resistance to tobramycin was reported. (6) The file on tobramycin includes no precise criteria for stopping treatment, and no data on the long-term impact of the observed increase in bacterial resistance. (7) The main adverse effects of tobramycin aerosol are tinnitus and voice changes. Deafness has also been reported. (8) The available assessment file does not show whether the risk-benefit ratio of tobramycin aerosol differs from that of other nebulised antibiotics used (off-licence) in this setting. However, tobramycin is the best-assessed nebulised antibiotic for this indication. (9) In practice, tobramycin solution for nebulisation may be considered the reference long-term treatment for chronic pulmonary infections due to P. aeruginosa in patients with cystic fibrosis. Assessment should continue, however, especially regarding the possible impact on mortality and the selection of resistant strains.     

Viscosity effects on nebulisation of aqueous solutions

While the viscosity of sucrose and sodium citrate solutions increased with increasing percentage (w/v) of solute, the surface tension largely remained consistent. Water, sucrose (10–60% w/v) and sodium citrate (7–36% w/v) solutions were nebulised in two air-jet nebulisers (Pari LC; Medix A II) operated at 6 1 min⁻¹ and in an ultrasonic device (Medix Electronic) operated at mid-power setting. A wide variation in nebuliser size and output characteristics existed between the different commercially available models studied. Contrary to atomisation theories for air-jet nebulisation, droplet size was inversely related to solution viscosity (over 1–6 cP). Beyond this critical value droplet size increased as viscosity increased. This anomaly may be due to viscosity acting either directly or through liquid flow-rates. By contrast the ultrasonic device generated droplets of size proportional to viscosity but was unable to nebulise high viscosity fluids (i.e. > 6 cP). The low viscosity solutions offered less resistance to the integral fountain disintegration process, thereby producing smaller droplets and higher outputs.