Droplet size distributions of nebulised aerosols for inhalation therapy

Attaching protein-adsorbing silica particles to the surface of cotton substrates for bioaerosol capture including SARS-CoV-2

The novel coronavirus pandemic (COVID-19) has necessitated a global increase in the use of face masks to limit the airborne spread of the virus. The global demand for personal protective equipment has at times led to shortages of face masks for the public, therefore makeshift masks have become commonplace. The severe acute respiratory syndrome caused by coronavirus-2 (SARS-CoV-2) has a spherical particle size of ~97 nm. However, the airborne transmission of this virus requires the expulsion of droplets, typically ~0.6-500 µm in diameter (by coughing, sneezing, breathing, and talking). In this paper, we propose a face covering that has been designed to effectively capture SARS-CoV-2 whilst providing uncompromised comfort and breathability for the wearer. Herein, we describe a material approach that uses amorphous silica microspheres attached to cotton fibres to capture bioaerosols, including SARS CoV-2. This has been demonstrated for the capture of aerosolised proteins (cytochrome c, myoglobin, ubiquitin, bovine serum albumin) and aerosolised inactivated SARS CoV-2, showing average filtration efficiencies of ~93% with minimal impact on breathability.

Pragmatic Randomized Trial of Corticosteroids and Inhaled Epinephrine for Bronchiolitis in Children in Intensive Care

OBJECTIVE

To determine whether the combination of systemic corticosteroids and nebulized epinephrine, compared with standard care, reduces the duration of positive pressure support in children with bronchiolitis admitted to intensive care.

STUDY DESIGN

We performed a pragmatic, multicenter, open-label, randomized trial between July 2013 and November 2019 in children younger than 18 months old with a clinical diagnosis of bronchiolitis. The intervention group received the equivalent of 13 mg/kg prednisolone over 3 days, then 1 mg/kg daily for 3 days, plus 0.05 mL/kg of nebulized 1% epinephrine made up to 6 ml with 0.9% saline via jet nebulizer and mask using oxygen at 12 l/min every 30 minutes for 5 doses, then 1-4 hourly for 3 days, then as required for 3 days. The primary outcome was clinician-managed duration of positive pressure support in intensive care defined as high-flow nasal-prong oxygen, nasopharyngeal continuous positive airway pressure, or mechanical ventilation.

RESULTS

In total, 210 children received positive pressure support. In the corticosteroid-epinephrine group, 107 children received positive pressure support for a geometric mean of 26 (95% CI, 22-32) hours compared with 40 (95% CI 34-47) hours in 103 controls, adjusted ratio 0.66 (95% CI 0.51-0.84), P = .001. In the intervention group, 41 (38%) children experienced at least 1 adverse event, compared with 39 (38%) in the control group.

CONCLUSIONS

In children with severe bronchiolitis, the duration of clinician-managed pressure support was reduced by regular treatment with systemic corticosteroids and inhaled epinephrine compared with standard care.

CLINICAL TRIAL REGISTRATION

Australian Clinical Trials Research Network: ACTRN12613000316707.

State-of-the-Art Review of The Application and Development of Various Methods of Aerosol Therapy

Aerosol therapy is a rapidly developing field of science. Due to a number of advantages, the administration of drugs to the body with the use of aerosol therapy is becoming more and more popular. Spraying drugs into the patient's lungs has a significant advantage over other methods of administering drugs to the body, including injection and oral methods. In order to conduct proper and effective aerosol therapy, it is necessary to become familiar with the basic principles and applications of aerosol therapy under various conditions. The effectiveness of inhalation depends on many factors, but most of all on: the physicochemical properties of the sprayed system, the design of the medical inhaler and its correct application, the dynamics of inhalation (i.e. the frequency of breathing and the volume of inhaled air). It is worth emphasizing that respiratory system diseases are one of the most frequently occurring and fastest growing diseases in the world. Accordingly, in recent years, a significant increase in the number of new spraying devices and pharmaceutical drugs for spraying has appeared on the market. It should also be remembered that the process of spraying a liquid is a complicated and complex process, and its efficiency is very often characterized by the use of micro- and macro parameters (including average droplet diameters or the spectrum of droplet diameter distribution). In order to determine the effectiveness of the atomization process and in the delivery of drugs to the patient's respiratory tract, the analysis of the size of the generated aerosol droplets is most often performed. Based on the proposed literature review, it has been shown that many papers dealt with the issues related to aerosol therapy, the selection of an appropriate spraying device, the possibility of modifying the spraying devices in order to increase the effectiveness of inhalation, and the possibility of occurrence of certain discrepancies resulting from the use of various measurement methods to determine the characteristics of the generated aerosol. The literature review presented in the paper was prepared in order to better understand the spraying process. Moreover, it can be helpful in choosing the right medical inhaler for a given liquid with specific rheological properties. The experimental data contained in this study are of great cognitive importance and may be of interest to entities involved in pharmaceutical product engineering (in particular in the case of the production of drugs containing liquids with complex rheological properties).

Comparison of plasma and pulmonary availability of chlorogenic acid, forsythiaside A and baicalin after intratracheal and intravenous administration of Shuang-Huang-Lian injection

ETHNOPHARMACOLOGICAL RELEVANCE

The off-label nebulization of Shuang-Huang-Lian (SHL) injection is often utilized to treat respiratory tract infections in China. However, the pulmonary biopharmaceutics of SHL was generally unknown, limiting the rational selection of therapeutic dose and dose frequency.

AIM OF THE STUDY

To characterize the size distribution of nebulized aerosols and to compare the pharmacokinetics and the lung distribution of three chemical makers of SHL, chlorogenic acid (CHA), forsythiaside A (FTA) and baicalin (BC), after intratracheal and intravenous administration of SHL to rats.

MATERIALS AND METHODS

The droplet size distribution profiles over nebulization process were dynamically monitored using a laser diffraction method whereas the levels of CHA, FTA and BC in plasma, lung tissues and bronchoalveolar lavage fluids (BALF) were determined by a validated LC-MS/MS assay. The pulmonary anti-inflammatory efficacy was evaluated using a lipopolysaccharide (LPS) induced lung inflammation model as indicated by the level of tumor necrosis factor-α (TNF-α) in BALF.

RESULTS

The nebulization of SHL showed good inhalability and allowed the aerosols to reach the upper or lower respiratory tract dependent on the performance of selected nebulizers. Following intratracheal administration of SHL at different doses, CHA, FTA and BC were absorbed into the bloodstream with the mean absorption time being 67.5, 63.5 and 114 min, respectively, rendering mean absolute bioavailabilities between 42.4% and 61.4% roughly independent of delivered dose. Relative to the intravenous injection, the intrapulmonary delivery increased the lung-to-plasma concentration ratios of CHA, FTA and BC by more than 100 folds and markedly improved the lung availability by 563-676 folds, leading to enhanced and prolonged lung retention. The production of TNF-α in BALF was decreased by ~50% at an intratracheal dose of 125 μL/kg SHL to LPS-treated mice.

CONCLUSION

The nebulization delivery of SHL is a promising alternative to the intravenous injection for the treatment of respiratory tract infections.

Development and evaluation of nanoemulsion and microsuspension formulations of curcuminoids for lung delivery with a novel approach to understanding the aerosol performance of nanoparticles

Extensive research has demonstrated the potential effectiveness of curcumin against various diseases, including asthma and cancers. However, few studies have used liquid-based vehicles in the preparation of curcumin formulations. Therefore, the current study proposed the use of nanoemulsion and microsuspension formulations to prepare nebulised curcuminoid for lung delivery. Furthermore, this work expressed a new approach to understanding the aerosol performance of nanoparticles compared to microsuspension formulations. The genotoxicity of the formulations was also assessed. Curcuminoid nanoemulsion formulations were prepared in three concentrations (100, 250 and 500 µg/ml) using limonene and oleic acid as oil phases, while microsuspension solutions were prepared by suspending curcuminoid particles in isotonic solution (saline solution) of 0.02% Tween 80. The average fine particle fraction (FPF) and mass median aerodynamic diameter (MMAD) of the nebulised microsuspension formulations ranged from 26% and 7.1 µm to 40% and 5.7 µm, for 1000 µg/ml and 100 µg/ml respectively. In a comparison of the low and high drug concentrations of the nebulised nanoemulsion, the average FPF and MMAD of the nebulised nanoemulsion formulations prepared with limonene oil ranged from 50% and 4.6 µm to 45% and 5.6 µm, respectively; whereas the FPF and MMAD of the nebulised nanoemulsion prepared with oleic acid oil ranged from 46% and 4.9 µm to 44% and 5.6 µm, respectively. The aerosol performance of the microsuspension formulations were concentration dependent, while the nanoemulsion formulations did not appear to be dependent on the curcuminoids concentration. The performance and genotoxicity results of the formulations suggest the suitability of these preparations for further inhalation studies in animals.

Drug Delivery Devices for Inhaled Medicines

Historically, the inhaled route has been used for the delivery of locally-acting drugs for the treatment of respiratory conditions, such as asthma, COPD, and airway infections. Targeted delivery of substances to the lungs has some key advantages over systemic administration, including a more rapid onset of action, an increased therapeutic effect, and, depending on the agent inhaled, reduced systemic side effects since the required local concentration in the lungs can be obtained with a lower dose. Fortunately, when designed properly, inhaled drug delivery devices can be very effective and safe for getting active agents directly to their site of action.

Challenging the two-minute tidal breathing challenge test

BACKGROUND

In the adenosine 5'-monophosphate (AMP) bronchial challenge test, AMP is usually administered according to dosing protocols for methacholine. We investigated whether the 2-min tidal breathing challenge test for methacholine is applicable to AMP. Parameters known to affect nebulizer output were studied. Our aim was to determine whether control of additional parameters is needed for currently standardized protocols.

METHODS

The study was performed with the Sidestream nebulizer from the APS Pro Aerosol Provocation System (CareFusion Respiratory). The effects of AMP concentration, jet pressure, and suction flow rate on nebulizer output rate and aerosol droplet size distribution were determined.

RESULTS

The volume median diameter for water increased from 5.10 μm to 8.49 μm when the jet pressure was reduced to obtain the prescribed output rate of 0.13 mL/min. The output rate was increased when a suction flow rate was used to remove the aerosol. Increasing the AMP concentration resulted in smaller droplets and a lower output rate when a suction flow was applied.

CONCLUSIONS

The effects of AMP concentration on nebulizer performance may result in changes in the administered dose and site of deposition of AMP at dose escalation. All of the investigated parameters influence nebulizer performance, hence the outcome of a bronchial challenge test. Therefore, these parameters should not only be specified in challenge testing, but be actively controlled as well.

Inhaled and intravenous treatment in acute severe and life-threatening asthma

Management of life-threatening acute severe asthma in children and adults may require anaesthetic and intensive care. The inhaled route for drug delivery is not appropriate when only small respiratory gas volumes are shifted; the i.v. route may be associated with greater side-effects. Magnesium sulphate i.v. has a place in acute asthma management because it is a mild bronchodilator, and has a stabilizing effect on the atria which may attenuate tachycardia occurring after inhaled and i.v. salbutamol. If intubation and ventilation are required, a reduction in bronchoconstriction by any means before and during these procedures should reduce morbidity. This narrative review aims to show strengths and weakness of the evidence, present controversies, and forward opinions of the author. The review contains a practical guide to the setting up, use and efficiency of nebulizers, metered dose inhalers, and spacers (chambers). It also presents a commonsense approach to the management of severe asthmatics in whom delay in bronchodilatation would cause clinical deterioration. When self-inhaled agents have had no effect, i.v. drugs may help avoid intubation and ventilation. The review includes suggestions for the use of inhaled anaesthetics, anaesthetic induction, and brief notes on subsequent ventilation of the lungs.

Study of nebulization delivery of aerosolized fluorescent microspheres to the avian respiratory tract

This study investigated the delivery of an aerosol of monodisperse microspheres to the respiratory tract of birds following aerosol exposure. Adult domestic pigeons (Columbia livia domestica, n = 5 birds per timed treatment) were exposed to an aerosol of fluorescent 1.0 microm diameter carboxylate microspheres for 0.5, 1, 2, or 4 hr. During the aerosolization period, the birds were free-standing in a plexiglass treatment chamber and the aerosol was delivered using a commercial nebulizer. Immediately following aerosol exposure, the birds were euthanatized and the carcasses were intravenously infused with a modified paraformaldehyde/gluteraldehyde fixative. Evaluation of microsphere distribution was performed using a stereoscopic microscope with an epifluorescent module. The results from this study revealed that the amount of aerosolized particles delivered using a commercial nebulizer was proportional to exposure periods. Aerosol exposure periods of 0.5 hr or 1 hr did not result in a readily observable distribution of 1.0 microm fluorescent microspheres to the cranial thoracic, caudal thoracic, or abdominal air sac membranes. This was partly attributed to the relatively low concentration of the individual monodisperse microspheres in the aerosolized suspension. The 2- and 4-hr exposure periods resulted in readily observable deposition of the 1.0 mirom fluorescent microspheres in the cranial thoracic, caudal thoracic, or abdominal air sac membranes, with the 4-hr exposure period resulting in the greatest number of particles on the membrane surfaces. For each of the exposure periods, there was individual animal variation regarding the distribution and relative number of spheres deposited. This study demonstrates the widespread deposition of particles that had an aerodynamic equivalent diameter of approximately 1 microm and provides a better understanding of particle deposition efficiency within the respiratory system following aerosol exposure in birds.

Clinical pharmacology and lesion penetrating properties of second- and third-line antituberculous agents used in the management of multidrug-resistant (MDR) and extensively-drug resistant (XDR) tuberculosis

Failure of first-line chemotherapy to cure tuberculosis (TB) patients occurs, in part, because of the development of resistance to isoniazid (INH) and rifampicin (RIF) the two most sterilizing agents in the four-drug regimen used to treat primary infections. Strains resistant to both INH and RIF are termed multidrug-resistant (MDR). Treatment options for MDR patients involve a complex array of twenty different drugs only two classes of which are considered to be highly effective (fluoroquinolones and aminoglycosides). Resistance to these two classes results in strains known as extensively drug-resistant (XDR) and these types of infections are becoming increasingly common. Many of the remaining agents have poorly defined pharmacology but nonetheless are widely used in the treatment of this disease. Several of these agents are known to have highly variable exposures in healthy volunteers and little is known in the patients in which they must be used. Therapeutic drug monitoring (TDM) is infrequently used in the management of MDR or XDR disease yet the clinical pharmacokinetic studies that have been done suggest this might have a large impact on disease outcome. We review what is known about the pharmacologic properties of each of the major classes of second- and third-line antituberculosis agents and suggest where judicious use of TDM would have the maximum possible impact. We summarize the state of knowledge of drug-drug interactions (DDI) in these classes of agents and those that are currently in clinical trials. Finally we consider what little is known about the ability of TB drugs to reach their ultimate site of action--the interior of a granuloma by penetrating the diseased lung area. Careful consideration of the pharmacology of these agents is essential if we are to avoid further fueling the growing epidemic of highly drug-resistant TB and critical in the development of new antituberculosis drugs.

A guinea pig model of acute and chronic asthma using permanently instrumented and unrestrained animals

To investigate mechanisms underlying allergen-induced asthmatic reactions, airway hyperresponsiveness and remodeling, we have developed a guinea pig model of acute and chronic asthma using unanesthetized, unrestrained animals. To measure airway function, ovalbumin (IgE)-sensitized animals are permanently instrumented with a balloon-catheter, which is implanted inside the pleural cavity and exposed at the neck of the animal. Via an external cannula, the balloon-catheter is connected to a pressure transducer, an amplifier, an A/D converter and a computer system, enabling on-line measurement of pleural pressure (P(pl))-closely correlating with airway resistance-for prolonged periods of time. Using aerosol inhalations, the method has been successfully applied to measure ovalbumin-induced early and late asthmatic reactions and airway hyperresponsiveness. Because airway function can be monitored repeatedly, intra-individual comparisons of airway responses (e.g., to study drug effects) are feasible. Moreover, this model is suitable to investigate chronic asthma and airway remodeling, which occurs after repeated allergen challenges. The protocol for establishing this model takes about 4 weeks.

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.

Production of radioactive particles for use in environmental studies

This paper presents an aerosol generation technique developed to produce dry aerosol particles of various sizes from aqueous solutions of salt. The technique was tested with sodium chloride, lithium carbonate and uranyl acetate at various aqueous concentrations which produced particles in the size range of 0.13-1.37 microm Mass Median Diameter (MMD). The generated aerosols were acceptably monodisperse with a geometric standard deviation of 1.4-2. Both MMD and Mass Median Aerodynamic Diameter (MMAD) increased significantly (p<0.001) with increased concentration of the salt in solution. The technique can also be used to generate aerosols of different chemical species. The results obtained indicate that the system is convenient for use with various aerosol-forming materials, with a stable particle size distribution being maintained for a long period of steady operation. The technique was successfully applied in wind tunnel studies to simulate the release of submicron radioactive particles and their interception by crops, grass and tree canopies. The relevance and application of the technique in other areas of environmental assessment studies is discussed.

The equivalence of compressor pressure-flow relationships with respect to jet nebulizer aerosolization characteristics

Manufacturers of aerosolized medications, approved by the Food and Drug Administration, specify the nebulizer(s) and compressor to be used with their product, in an attempt to achieve efficacy comparable to that obtained in the clinical trials. The need to limit the compressor to that used in the trials has not been investigated in detail. We suggest a technique to determine the equivalency of different compressors such that a chosen nebulizer's performance is not significantly altered. Aerosol particle size (MMD) was measured with a laser; compressor flow and pressure were measured with a mass flow meter and pressure gauge, respectively. For all models of nebulizer, increased flow or driving pressure caused a decrease in aerosol MMD. The flow resistance of nebulizer models varied, and the flow output of compressors decreased as imposed nebulizer resistance increased. However, for any specific compressor-nebulizer combination there is a unique flow and pressure, and the nebulizer generates a given MMD. We demonstrate methods to choose alternate compressors that may be used to drive a nebulizer and yet keep the nebulizer's MMD and performance within predetermined limits. Once an acceptable range of variance in a nebulizer's MMD is defined, alternate compressors may be safely chosen. We recommend that these techniques be used by manufacturers of medications and of compressors to safely determine the acceptability of several rather than a single model compressor to drive a chosen nebulizer. The techniques assure consistency of the nebulizer's clinically demonstrated performance characteristics.

Formulation of aerosolized therapeutics

Pseudomonas aeruginosa (PA), which colonizes the airways of approximately 90% of patients with cystic fibrosis (CF) at some point during their lives, is an important contributor to the vicious cycle of infection and inflammation leading to bronchiectasis and eventual respiratory failure. Oral antibiotic therapy is often ineffective in treating PA infections. Instead, in-hospital IV aminoglycoside therapy administered in combination with other IV antibiotics, such as beta-lactams or quinolones, is the mainstay of treatment. The specific chemical and physical properties of CF sputum require high serum antibiotic levels for effective antimicrobial treatment; however, IV aminoglycoside therapy is associated with an increased risk of ototoxicity and nephrotoxicity. In an attempt to avoid systemic toxicity and effectively treat PA infections, clinicians have combined IV antibiotics with sterile solutions of saline or water to aerosolize the mixture for inhalation. Experience with such "home brews" has clearly demonstrated that IV preparations are neither intended nor medically indicated for inhalation. Patients may experience coughing, mucosal irritation, or bronchospasm in response to the preservatives, stabilizing agents, and other additives commonly found in IV preparations. While the rationale for aerosolized drug delivery remains compelling, concerns about uniform dose delivery, ineffective nebulization, and therapeutic adherence arise. Since the 1940s, when these efforts began, ongoing research and clinical trials have identified several additional factors affecting inhaled drug delivery and deposition in the airways. This article chronicles some of the challenges faced by researchers and elucidates factors critical to the reformulation of a safe and effective antibiotic solution for aerosolized delivery.

In Vitro Characteristics of Tobramycin Aerosol from Ultrasonic and Jet Nebulizers

STUDY OBJECTIVE

To compare the in vitro performance of an ultrasonic nebulizer and a jet nebulizer in producing a respirable aerosol of tobramycin solution for injection.

DESIGN

In vitro observational study

DEVICES

Ultrasonic and jet nebulizers.

INTERVENTION

Output was determined by measuring the difference in nebulizer weight before and after nebulizing 3 ml of tobramycin injection solution. Mass median aerodynamic diameter (MMAD) and respirable mass were determined by sampling tobramycin aerosol into a cascade impactor.

MEASUREMENTS AND MAIN RESULTS

Mean (SD) output was 1.14 (0.09) ml/minute for the ultrasonic nebulizer and 0.64 (0.08) ml/minute (p<0.001) for the jet nebulizer. Mean MMAD for the jet nebulizer (2.31 [0.10] microm) was less than that of the ultrasonic nebulizer (2.81 [0.17] microm, p<0.001). The majority of tobramycin aerosol produced was in the respirable range for both the ultrasonic (65.1% [4.10%]) and jet (60.6% [0.73%], p=0.008) nebulizers.

CONCLUSION

Despite small, clinically unimportant differences in aerosol size and respirable fraction, either device would be acceptable to administer tobramycin injection solution.

The choice of compressor effects the aerosol parameters and the delivery of tobramycin from a single model nebulizer

Recent U.S. Phase III trials of the aerosolized delivery of tobramycin to cystic fibrosis (CF) patients demonstrated a significant improvement in pulmonary function and in sputum bacterial density. These trials used the Pari LC Plus nebulizer and DeVilbiss Pulmo-Aide compressor. This compressor is not generally available in Europe, and its power requirements do not match the European power supply. Thus alternate compressors were evaluated, using the LC Plus nebulizer, in preparation for European clinical trials. Aerosol particle size distribution, nebulization time (min), and the respirable dose of tobramycin (mg within 1-5 mu) were obtained for seven compressor models. The respirable quantity delivered by each of the European compressors (240 Volts, 50 Hz) was compared to the LC Plus and PulmoAide compressor (120 Volts, at 60 Hz). The U.S. system delivered 71.4 mg of the 300 mg instilled dose within the respirable range; using the European compressors, between 63.0 and 74.8 mg was delivered. With a 97% confidence that the delivered tobramycin was within 20% of the standard, we conclude that the SystAm 23ST, MedicAid CR50 and CR60, Pari Master and the Pari Boy compressors are equivalent to the U.S. standard; the Hercules and the SystAm 26ST compressors were not statistically equivalent to the standard. Using the LC Plus nebulizer, five European compressors delivered doses of TOBI that are similar to the doses delivered by the DeVilbiss PulmoAide compressors, and thus may be expected to produce clinical results similar to those of the U.S. trials.

The effect of breathing frequency on deposition of drug aerosol using an inhalation-synchronized dosimeter in healthy adults

The deposition of inhaled drug aerosol between the tongue, the upper and lower respiratory tract, the lungs and the gastrointestinal tract (GI tract) in 11 healthy adults was studied by using a nebulizer with an inhalation-synchronized dosimeter. The effect of breathing frequency on deposition was studied using radioaerosol (mixture of salbutamol and technetium bound to diethylenetriamine pentacetate, [99mTc]DTPA) and a gamma-camera. In healthy subjects who were breathing at their own frequency (16 +/- 5 breaths min-1, mean +/- SD), the proportion of inhaled aerosol deposited in the lungs was 48 +/- 14 (mean percentage +/- SD). The proportion deposited in the upper airway tract and the GI tract was 19 +/- 13 and 25 +/- 9 respectively, and the remainder was deposited on the tongue (6 +/- 4) and in the lower airway tract (3 +/- 2). Guided, slower breathing frequency (11 +/- 5 breaths min-1) changed the deposition remarkably. The proportion of the pulmonary deposition of the inhaled dose increased significantly (P < 0.004) to 60 +/- 17, and the proportion of the upper airway tract deposition decreased significantly (P < 0.005) by half of the initial deposition. We conclude that a slow controlled breathing frequency is an important factor if we want to increase the drug deposition in the lungs. It is also essential in decreasing the variation in the deposition of the lungs.

Inhalation of the nitric oxide synthase cofactor tetrahydrobiopterin in healthy volunteers

Pulmonary endothelial dysfunction is the hallmark of acute lung injury. Impaired pulmonary endothelial nitric oxide (NO) production in this event has been described. Tetrahydrobiopterin (BH4) is an essential cofactor for NO synthase and modulator of its activity. At high local concentrations, BH4 provokes local vasodilation in vivo in healthy individuals. At lower concentrations, BH4 selectively and locally restores disturbed NO-dependent vasodilation in patients with endothelial dysfunction. In this preliminary study, we therefore investigated the feasibility of BH4 inhalation in five healthy human volunteers. Inhalation of buffered, aqueous BH4-dihydrochloride solution was well tolerated; despite the buffer, BH4 stability was completely preserved. Resorption of inhaled BH4 was demonstrated by significantly increased BH4 levels in plasma and urine. Inhaled BH4 did not alter pulmonary function and had no effect on systemic hemodynamic values. Our data demonstrate that inhalation is a novel method for local BH4 administration, offering a basic therapeutic tool for investigation of restoration of impaired NO-dependent vasodilation due to pulmonary endothelial dysfunction.

Aerosol deposition in infants with cystic fibrosis

Twenty asymptomatic infants with cystic fibrosis (CF) were studied to determine the amount of radiolabeled aerosol [99m technetium diethylenetriamine penta acetic acid (Tc99m DTPA)] deposited in the respiratory system and its distribution. Aerosols were generated by jet nebulization systems that were used in the wards and the laboratory. Subjects were studied in three groups: group A (n = 10) was sedated with chloral hydrate; children inhaled an aerosol of 7.7 microns mass median diameter (MMD); group B (n = 5) was not sedated, using the same nebulization system (same aerosol particle size as group A); and group C (n = 5) was not sedated; these children inhaled an aerosol with an MMD of 3.6 microns. Normal saline plus 4 mCi of Tc99m bound to DTPA was added to each nebulizer. A closed system was used to collect the expired aerosol. Radioactivity in each infant and in the equipment was measured with a gamma camera on completion of nebulization. In groups A and B, the percentages of the total dose deposited in the lung were 0.97 +/- 0.35% and 0.76 +/- 0.36%, respectively. In group C, 2.0 +/- 0.71% was deposited in the lung (P < 0.01). Deposition in the nose, mouth, and pharynx was least in group C (P < 0.01). In groups A and B, the intrathoracic deposition occurred predominantly in the trachea and main bronchi, whereas in group C, significantly more aerosol was deposited in the lung region. There was marked inter-subject variability in the percentage of aerosol deposition within the three groups. There was no correlation between percentage of aerosol deposited in the respiratory system and age, height, or weight. Sedation did not have a significant effect on deposition of aerosol in infants. This study indicates that only a small proportion of nebulized solution is deposited in the lungs of infants and that this proportion is influenced by the particle size of the aerosol. The smaller particle size (3.6 microns MMD) was deposited in the lung better than large particles.

Why do medical nebulizers differ in their output and particle size characteristics?

Previous work done on the characterisation of nebulizers has focused on gravimetrical output and particle/droplet size distribution at various air flow rates. This paper investigates six different nebulizers, with regard to droplet generation and separation properties, at a single air flow rate. Droplet generation and separation properties were measured with laser diffraction and impactor techniques. For each of the nebulizers the air velocity was calculated and both liquid and air volumetric flow rate was measured. The primary generated droplets (nebulizer without impaction baffle) had a mean size of between 15 microns and > 500 microns. The secondary generated droplets (nebulizer with baffle) were in the size range of 1 to 10 microns. It was found that the baffle system of the investigated nebulizers could be described according to ordinary impaction theory. The mass median diameters (MMD) of these nebulizers were found to be dependent on air velocity (vg), and ratio of liquid to air volumetric flow rate (Ql/Qa). In all of the nebulizers, between 93% and 99% of the generated primary droplets were caught by the baffle system which resulted in a very low output. Thus, the nebulizers examined do not appear to be optimised, with regard to observed droplet generation and baffle arrangements, if secondary droplets with a size approximately 1 micron are desired. By changing the design at the primary generation point, air velocity (vg) and liquid to air flow rate (Ql/Qa), the primary generated droplet size could be decreased. This would result in an increase in the number concentration of smaller droplets that pass the baffle system.(ABSTRACT TRUNCATED AT 250 WORDS)

Nebuliser performance, pharmacokinetics, airways and systemic effects of salbutamol given via a novel nebuliser delivery system ("Ventstream")

BACKGROUND

Currently available nebulisers are inefficient and show variable aerosol deposition in the lung owing to the differences in the particle size generated. The aim of this study was to compare systemic absorption and bronchodilator effects of salbutamol given via a novel ("Ventstream") and a conventional ("Hudson Updraft II") nebuliser system, having initially evaluated the performance of both nebulisers in vitro. The "Ventstream" nebuliser uses a one way valve system to provide an additional inspiratory side flow to match aerosol delivery with tidal volume.

METHODS

Nebuliser output and particle distribution from 10 Ventstream and 10 Hudson nebulisers were compared in vitro. Eight asthmatic patients, FEV1 55(2)% predicted, were then randomised to receive salbutamol via Ventstream or Hudson nebulisers on separate days. On each day cumulative doses of inhaled salbutamol were given: 1.25 mg, 2.5 mg (1.25 + 1.25 mg), and 5.0 mg (2.5 + 2.5 mg). Airways responses, systemic responses, and plasma salbutamol concentrations were measured at each dose and for up to 240 minutes after the final dose.

RESULTS

The in vitro comparison showed a greater respirable fraction with a higher percentage volume of particles < 5 microns in diameter using Ventstream than Hudson nebulisers (mean (95% CI) for difference): 25.4% (95% CI 22.4% to 28.3%), and a higher aerosol rate of output: 0.08 g/min (95% CI 0.05 to 0.11 g/min). At the 5.0 mg dose the Ventstream produced a twofold greater concentration of plasma salbutamol than the Hudson nebuliser (AUC0-240): 392.1 ng/ml.min (95% CI 240.6 to 543.6 ng/ml.min). There was a higher AUC0-240 for PEFR with the Ventstream than with the Hudson nebuliser: 74.161 x 10(2) (95% CI 39.50 to 108.821 x 10(2). For FEV1 and FEV25-75 there was a difference in the peak response between the 5.0 mg and 2.5 mg doses with the Ventstream only. Extrapulmonary beta 2 responses were greater with the Ventstream than with the Hudson at 2.5 mg and 5.0 mg doses, although the differences did not appear to be clinically relevant.

CONCLUSIONS

The Ventstream produced a twofold increase in the delivery of salbutamol to the lung compared with the Hudson nebuliser, and there was an associated increase in systemic beta 2 responses with an improvement in some parameters of bronchodilator efficacy. As a consequence of improved delivery with the Ventstream, it may be possible to halve the drug dose to produce similar bronchodilator efficacy at reduced cost. Further studies are required to evaluate the value of the Ventstream for delivery of nebulised antibiotics and corticosteroids.

Effect of inhaled frusemide on responses of airways to bradykinin and adenosine 5'-monophosphate in asthma

BACKGROUND

Inhaled frusemide exerts a protective effect against bronchoconstriction induced by several indirect stimuli in asthma. This effect could be caused by interference with neural pathways. The effect of inhaled frusemide on bronchoconstriction induced by inhaled bradykinin, which is thought to cause bronchoconstriction via neural mechanisms, was studied and compared with the effects of adenosine 5'-monophosphate (AMP) which probably produces its airway effects by augmenting mast cell mediator release and interfering with neural pathways.

METHODS

Patients first underwent AMP and bradykinin challenges. They were then studied in a randomised, placebo controlled, double blind fashion. Ten atopic asthmatic subjects, studied on four days, were pretreated with inhaled frusemide (40 mg) or placebo for 10 minutes, five minutes before challenge with increasing concentrations of nebulised AMP or bradykinin.

RESULTS

On the open visit days the provocative concentrations required to reduce forced expiratory volume in one second (FEV1) by 20% from baseline (PC20) for AMP and bradykinin were 16.23 (1.42-67.16) and 2.75 (0.81-6.6) mg/ml. There was a significant correlation between baseline AMP and bradykinin PC20 values. For AMP the geometric mean PC20 values following pretreatment with inhaled frusemide and matched placebo were 80.97 (9.97- > 400.0) and 14.86 (2.6-104.6) mg/ml respectively (95% CI 0.49 to 0.98). For bradykinin the geometric mean PC20 values following pretreatment with inhaled frusemide and matched placebo were 13.22 (2.53- > 16.0) and 2.52 (0.45-5.61) mg/ml respectively (95% CI 0.43 to 1.01). Frusemide afforded 5.45 and 5.24 fold protection against AMP and bradykinin-induced bronchoconstriction respectively. Furthermore, there was a significant correlation between protection afforded to the airways against AMP and bradykinin.

CONCLUSIONS

These data suggest that inhaled frusemide affords protection against bradykinin-induced bronchoconstriction which is comparable to that against AMP, supporting a common mechanism of action for frusemide.

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

Nebulized antibiotic therapy in cystic fibrosis is an established procedure. The present study was designed to quantitate deposition, and assess its relation to the disease state. Twenty seven children and young adults with cystic fibrosis (mean 11.6 years, range 4-23 years, 12 females) were studied to establish the quantity and pattern of deposition of nebulized tobramycin in the respiratory tract. A single (120 mg) dose of nebulized 99 m technetium-labelled tobramycin was administered, and imaged with a gamma-camera. The mean penetration index (which compares the distribution of 81 m-Krypton gas with Tc-radioaerosol) was also used to measure peripheral deposition efficiency. The aerosol mass median diameter (MMAD) for the compressor-nebulizer system used was 5.3 u, measured with the Malvern Mastersizer. Serial sputum samples were fluroimmunoassayed for tobramycin in nine patients. A mean of 8.0 (SEM 1.0) mg tobramycin reached the lungs. There was no relationship between the total pulmonary deposition and indices of pulmonary damage in cystic fibrosis. Sixteen percent of the lung tobramycin reached the periphery. The greater the lung damage as indicated by FEV1 and Chrispin-Norman scores, the smaller the proportion of pulmonary tobramycin that reached the periphery. The mean penetration index increased with increase in the FRC, but bore no relation to other respiratory function tests or to chest X-ray scores. Sputum tobramycin concentrations reached levels bactericidal for Pseudomonas aeruginosa. Airway obstruction and damage affected the proportion of pulmonary tobramycin reaching the periphery. The proportion of tobramycin reaching the lungs was small and variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Aprotinin aerosol treatment of influenza and paramyxovirus bronchopneumonia of mice

The therapeutic efficacy of aerosolized aprotinin, a natural proteinase inhibitor, against influenza and paramyxovirus bronchopneumonia of mice is shown. Small-particle aerosol of aprotinin solution was generated by a Collison type nebulizer and infected mice were exposed to aerosol atmosphere by four 30-40 min incubations per day for 6 days. This regimen provided an inhalation aprotinin dosage of approx. 6 micrograms/mouse/day. With such treatment more than 50% of mice infected with lethal doses of either influenza virus or paramyxovirus were protected from death. A suppression of the development of fatal hemorrhagic bronchopneumonia and a normalization of the body weight gain were observed in infected mice treated with aerosolized aprotinin. These data suggest that low doses of aerosolized proteinase inhibitors could be successfully applied against respiratory influenza-like virus diseases.

Operating characteristics of 18 different continuous-flow jet nebulizers with beclomethasone dipropionate liposome aerosol

A study of 18 different commercially available continuous-flow, jet nebulizers was performed with a standard liposomal formulation of beclomethasone dipropionate (Bec-DP) prepared with dilauroyl phosphatidylcholine (Bec-DLPC). The analysis compared the total Bec-DP output from aqueous suspensions of Bec-DLPC containing an initial starting reservoir concentration of 0.5 mg/ml. Aerosols from each nebulizer tested were characterized by the mass median aerodynamic diameter, geometric standard deviation, drug output, and the predicted percentage regional deposition of inhaled Bec-DLPC liposomes within the human respiratory tract. These data can provide a basis for the selection of commercially available jet nebulizers for use with glucocorticoid liposome aerosols for treatment of asthma and other inflammatory lung diseases.

Comparison of nebulised aerosol deposition in the lungs of healthy adults following oral and nasal inhalation

A standard jet nebuliser was used to generate a radiolabelled aerosol and the pattern of deposition within the airways of eight healthy adults was studied with a gamma camera. Penetration of aerosol to the lung was greatly reduced when breathing through the nose compared with mouth breathing.

Lung deposition from four nebulizers

The total and regional deposition of aerosol has been compared using four nebulizers; the Pari Boy 37.80, Pari IS-2, RespirGard II and Penta-Sonic. The aerosol was radiolabelled with [99Tcm]DTPA, administered to ten healthy subjects and the distributions monitored by gamma scintigraphy. Median lung aerosol depositions expressed as percentages of the doses initially loaded into the nebulizers were: Pari IS-2 19%, Pari Boy 37.80 13%, RespirGard II 9% and Penta-Sonic 2%. The ratios of the peripheral to central lung deposition, however, were greater with the RespirGard II and Penta-Sonic nebulizers. The choice of the most appropriate nebulizer depends on the pharmaceutical being administered, since aerosol must be delivered to the required site in sufficient quantity, whilst minimizing the incidence of local or systemic side-effects.

Drug delivery from jet nebulisers

Maximising the rate of drug delivered in particles small enough to reach the lower respiratory tract from jet nebulisers may allow treatment times to be reduced and thus improve the acceptability of this form of treatment, particularly in very young patients. The role of various technical factors such as driving gas flow (DGF) in determining the rate of drug delivery was studied by constructing a model to simulate the respiratory pattern of individuals with different tidal volumes using a Starling ventilator and filter. Sodium cromoglycate was nebulised under a variety of operating conditions and the dose deposited on the filter was assayed. Tidal volumes of 50 and 400 ml were used at a frequency of 32 breaths per minute. Increasing the DGF from 4 to 8 l/minute produced a 264% increase in the rate of drug output but only a 32% increase in aerosol concentration. The mass of drug contained within droplets less than 5 microns increased from 26.8% to 70.8% of the total. The resultant increase in rate of drug delivery to the filter was 34% for a tidal volume of 50 ml and 79% for a tidal volume of 400 ml though the dose contained within droplets less than 5 microns increased by 4-fold at 50 ml tidal volume and by more than 5-fold at the higher tidal volume. Halving the solution concentration halved the rate of drug delivery. Increasing the tidal volume 8-fold from 50 to 400 ml resulted in an increase in the rate of drug deposition upon the filter of only 2.2 to 3-fold depending upon the DGF so that substantially more drug per ml inhaled was delivered at the lower tidal volume. These results are explained by considering factors that influence the rate of drug delivery. At low tidal volumes the rate of drug delivery at a given respiratory rate is dependent on the tidal volume and aerosol concentration. At high tidal volumes it is dependent upon aerosol concentration and volume of available aerosol and is essentially independent of tidal volume.

The effect of respiratory manoeuvres and pharmacological agents on the pharmacokinetics of nedocromil sodium after inhalation

1. Eight healthy subjects inhaled nedocromil sodium from a metered-dose inhaler using a standardised inspiratory technique. Blood samples were taken for up to 270 min after inhalation for radioimmunoassay of plasma nedocromil sodium concentrations. 2. To investigate the possibility that respiratory manoeuvres can alter the absorption of the drug from the lungs, on the first (control) study day at 70 min after dosing, subjects performed nine forced expiratory manoeuvres over a 3 min period. At 110 min after dosing, subjects took a slow, full inspiration with a 30 s breath-hold, and at 150 min after dosing the subjects performed one single forced expiration. 3. On the second study day, subjects inhaled methoxamine, 0.15 mg kg-1 of a 20 mg ml-1 solution at 60 min after dosing, and the study continued as above. On the third day, subjects repeated the sequence of respiratory manoeuvres, after having taken phenoxymethyl penicillin and probenecid by mouth for 48 h. 4. Both multiple forced expirations and the deep inspiration with breath-hold produced significant increases in the absorption of nedocromil sodium. Inhaled methoxamine did not alter airway calibre or the response to the respiratory manoeuvres. Probenecid, but not penicillin, was detected in the subjects' plasma, and had the effect of increasing the rise in plasma nedocromil sodium concentrations after the multiple forced expirations when compared with the control day. 5. These data suggest that disruption of epithelial tight junctions induced by the respiratory manoeuvres leads to enhanced paracellular transport of nedocromil sodium into the draining circulation of the airways and alveoli.(ABSTRACT TRUNCATED AT 250 WORDS)

A non-bronchoconstrictor, bacteriostatic preservative for nebuliser solutions

We have studied the bacteriostatic and airways effects of the preservatives chlorocresol and chlorbutol, to assess if they may be safely used in nebuliser solutions. The bacteriostatic study was carried out according to standard techniques, and the preservatives were able to inhibit the growth of a range of bacteria and yeasts for a period of 28 days. The airways effects were studied in eight asthmatic subjects, who were challenged with either the preservatives or saline (as placebo). Pulmonary function was followed as FEV1 for 60 min after inhalation, and there was no change in FEV1 following inhalation. We conclude that these preservatives may be used safely in nebuliser solutions.

Aerosol therapy in AIDS

Pneumocystis carinii pneumonia (PCP) is the most common presenting symptom in patients with the acquired immunodeficiency syndrome (AIDS). Clinical trials have shown that inhaled pentamidine, delivered by nebulizer, is an effective prophylaxis for PCP in high-risk patients, and can be used to treat mild to moderate episodes. Side effects are minor, in marked contrast to the parenteral route of administration. The choice of nebulizer system will determine both alveolar delivery of pentamidine and the incidence of cough related to deposition of droplets on large conducting airways. Radioaerosol studies have suggested that optimum nebulizer systems for inhaled pentamidine deliver the majority of the aerosol mass in droplets smaller than 2 microns diameter, ideal for alveolar penetration.

Platelet activating factor does not cause a reproducible increase in bronchial responsiveness in normal man

The reproducibility of acute effects of inhaled PAF on airway calibre, circulating neutrophil count and any subsequent increase in bronchial responsiveness has been studied in six normal subjects and compared to the effects of inhaled lyso-PAF, the inactive precursor and metabolite of PAF. PAF caused acute bronchoconstriction and a transient fall in neutrophil count on two separate occasions in five out of six subjects (minimum percentage of baseline values (mean): first PAF challenge; sGaw 69%, Vmax30 72%; neutrophil count 70%; second PAF challenge; sGaw 61%, Vmax30 74%, neutrophil count 63%). In one subject inhaled PAF caused bronchoconstriction and a transient fall in neutrophil count once, but a second challenge resulted in no detectable changes. There was no significant increase in bronchial responsiveness to methacholine in any subject studied on five occasions over a 2-week period following each PAF challenge. Challenge with lyso-PAF did not cause acute effects or any subsequent changes in bronchial responsiveness. These findings demonstrate that any effects of inhaled PAF on bronchial responsiveness in normal man are small and probably not of clinical significance. It would also be inappropriate to use this human model to study the mechanisms of bronchial hyperresponsiveness or for the preliminary assessment of potential new anti-asthma drugs.

Droplets produced by medical nebulizers. Some factors affecting their size and solute concentration

The effect of nebulizer solution temperature and dilution air humidity on the size and solute concentration of aqueous aerosol droplets were studied. Four combinations of jet-nebulizers with air compressors or oxygen sources and one ultrasonic nebulizer were tested. The temperature to which the nebulizer solution of each system fell during generation was measured. The nebulizers were then kept at set temperatures, generated aerosols collected and either droplet size or solute concentration measured. The droplet solute concentration was found to increase. The droplet size decreased along with the droplet solute concentration increase. The ultrasonic nebulizer also was tested: its high output made the concentration of the solution in the droplets much more stable. However, the proportion of droplets depositing in the tubing and valves changed markedly with aerosol flow rate. The potential for large changes in droplet solute concentration, droplet size and output during nebulization should be considered in therapeutic and diagnostic applications of nebulized aerosols.