Performance Testing of a Homemade Aerosol Generator for Pulmonary Administration of Dry Powder Formulations to Mice.

A challenge in the development of dry powder formulations for inhalation is the poor reproducibility of their administration to small laboratory animals. The currently used devices for the pulmonary administration of dry powder formulations to small rodents often function sub-optimally as they use the same puff of air for both powder dispersion and aerosol delivery. As a result, either the air volume and flow rate are too low for complete powder deagglomeration or they are too high for effective aerosol delivery to the lungs of the animal. Therefore, novel and better devices are desired. We here present an aerosol generator designed to administer a pre-generated aerosol to the lungs of mice. By mapping the complex relationship between the airflow rate, delivery time and emitted dose, we were able to control the amount of powder being delivered from the aerosol generator. The emitted aerosol had a size range favorable for lung deposition and could be measured reproducibly. Nevertheless, in vivo fluorescent imaging still revealed considerable differences between the mice in terms of the dose deposited and the distribution of powder over the lungs, suggesting that a certain biological variation in lung deposition is inevitable.

Pulmonary immunization: deposition site is of minor relevance for influenza vaccination but deep lung deposition is crucial for hepatitis B vaccination.

Vaccination via the pulmonary route could be an attractive alternative to parenteral administration. Research towards the best site of antigen deposition within the lungs to induce optimal immune responses has conflicting results which might be dependent on the type of vaccine and/or its physical state. Therefore, in this study, we explored whether deep lung deposition is crucial for two different vaccines, i.e., influenza and hepatitis B vaccine. In view of this, influenza subunit vaccine and hepatitis B surface antigen were labeled with a fluorescent dye and then spray-dried. Imaging data showed that after pulmonary administration to mice the powders were deposited in the trachea/central airways when a commercially available insufflator was used while deep lung deposition was achieved when an in-house built aerosol generator was used. Immunogenicity studies revealed that comparable immune responses were induced upon trachea/central airways or deep lung targeting of dry influenza vaccine formulations. However, for hepatitis B vaccine, no immune responses were induced by trachea/central airways deposition whereas they were considerable after deep lung deposition. Thus, we conclude that deep lung targeting is not a critical parameter for the efficacy of pulmonary administered influenza vaccine whereas for hepatitis B vaccine it is.

Targeting the small airways with dry powder adenosine: a challenging concept.

Background: Small-particle inhaled corticosteroids (ICS) provide a higher small airway deposition than large-particle ICS. However, we are still not able to identify asthma patients who will profit most from small-particle treatment. Objective: We aimed to identify these patients by selectively challenging the small and large airways. We hypothesized that the airways could be challenged selectively using small- and large-particle adenosine, both inhaled at a high and a low flow rate. Design: In this cross-over study 11 asthma subjects performed four dry powder adenosine tests, with either small (MMAD 2.7 µm) or large (MMAD 6.0 µm) particles, inhaled once with a low flow rate (30 l min-1) and once with a high flow rate (60 l min-1). Spirometry and impulse oscillometry were performed after every bronchoprovocation step. We assumed that FEV1 reflects the large airways, and FEF25-75%, R5-R20 and X5 reflect the small airways. Results: The four adenosine tests were not significantly different with respect to the threshold values of FEV1 (p = 0.12), FEF25-75% (p = 0.37), R5-R20 (p = 0.60) or X5 (p = 0.46). Both small- and large-particle adenosine induced a response in the small airways in the majority of the tests. Conclusions: In contrast to our hypothesis, all four adenosine tests provoked a response in the small airways and we could not identify different large- or small-airway responders. Interestingly, even the test with large particles and a high flow rate induced a small-airway response, suggesting that selective challenging of the small airways is not necessary. Future studies should investigate the relation between particle deposition and the site of an airway response.

Prerequisites for a dry powder inhaler for children with cystic fibrosis.

Correct inhalation technique is essential for effective use of dry powder inhalers (DPIs), as their effectiveness largely depends on the patient's inhalation manoeuvre. Children are an especially challenging target population for DPI development due to the large variability in understanding and inspiratory capacities. We previously performed a study in which we determined the prerequisites for a paediatric DPI in a mostly healthy paediatric population, for which we used an empty test inhaler with variable internal airflow resistance and mouthpiece. In the current study we investigated what specifications are required for a DPI for children with cystic fibrosis (CF), for which we expanded on our previous findings. We recorded flow profiles of 35 children with CF (aged 4.7-14.7 years) at three airflow resistances (0.031-0.045 kPa0.5.min.L-1) from which various inspiratory parameters were computed. Obstructions in the mouth during inhalation were recorded with a sinuscope. All children were able to perform a correct inhalation manoeuvre, although video analysis showed that children did not place the inhaler correctly in the mouth in 17% of the cases. No effect was found of medium to high airflow resistance on total inhaled volume, which implies that the whole resistance range tested is suitable for children with CF aged 4-14 years. No effect could be established of either mouthpiece design or airflow resistance on the occurrence of obstructions in the mouth cavity. This study confirms our previous conclusion that the development of DPIs specifically for children is highly desired. Such a paediatric DPI should function well at 0.5 L inhaled volume and a peak inspiratory flow rate of 20 to 30 L/min, depending on the internal airflow resistance. This resistance can be increased up to 0.045 kPa0.5.min.L-1 (medium-high) to reduce oropharyngeal deposition. A higher resistance may be less favourable due to its compromising effect on PIF and thereby on the energy available for powder dispersion.

Tolerability and Pharmacokinetic Evaluation of Inhaled Dry Powder Tobramycin Free Base in Non-Cystic Fibrosis Bronchiectasis Patients.

RATIONALE: Bronchiectasis is a condition characterised by dilated and thick-walled bronchi. The presence of Pseudomonas aeruginosa in bronchiectasis is associated with a higher hospitalisation frequency and a reduced quality of life, requiring frequent and adequate treatment with antibiotics. OBJECTIVES: To assess local tolerability and the pharmacokinetic parameters of inhaled excipient free dry powder tobramycin as free base administered with the Cyclops dry powder inhaler to participants with non-cystic fibrosis bronchiectasis. The free base and absence of excipients reduces the inhaled powder dose. METHODS: Eight participants in the study were trained in handling the device and inhaling correctly. During drug administration the inspiratory flow curve was recorded. Local tolerability was assessed by spirometry and recording adverse events. Serum samples were collected before, and 15, 30, 45, 60, 75, 90, 105, 120 min; 4, 8 and 12 h after inhalation. RESULTS AND DISCUSSION: Dry powder tobramycin base was well tolerated and mild tobramycin-related cough was reported only once. A good drug dose-serum concentration correlation was obtained. Relatively small inhaled volumes were computed from the recorded flow curves, resulting in presumably substantial deposition in the central airways-i.e., at the site of infection. CONCLUSIONS: In this first study of inhaled dry powder tobramycin free base in non-cystic fibrosis bronchiectasis patients, the free base of tobramycin and the administration with the Cyclops dry powder device were well tolerated. Our data support further clinical studies to evaluate safety and efficacy of this compound in this population.

A levodopa dry powder inhaler for the treatment of Parkinson's disease patients in off periods.

Adequate treatment of Parkinson's patients in off periods with orally administered levodopa is hindered by a poor bioavailability and a slow onset of action. Hence, there is a need for a fast and reliable alternative as for instance via pulmonary administration of the drug. We developed a levodopa containing powder formulation for pulmonary delivery by a recently presented high dose dry powder inhaler (Cyclops). The objective was to produce the drug formulation by means of simple techniques such as micronization, either as pure active substance or with a minimum amount of excipients. After an initial screening on dispersion behaviour, the most promising formulation in the Cyclops was characterized in vitro over a range of pressure drops (2-6 kPa) and doses (20, 30 and 40 mg), representative of those to be expected in practice. A co-micronized levodopa formulation with 2% L-leucine appeared to yield the best aerosol properties for inhalation and highest delivered dose reproducibility. The combination of this particular formulation and the Cyclops inhaler seems to meet the basic requirements for satisfactory deposition in the airways. This formulation is therefore expected to be a promising candidate for the treatment of Parkinson's patients in an off period.

Can 'extrafine' dry powder aerosols improve lung deposition?

There is increasing interest in the use of so-called 'extrafine' aerosols to target the small airways in the management of asthma and COPD. Using previously presented deposition data, we assessed whether submicron (<1µm) particles can improve central and deep lung deposition. Our data show instead that particles in the range 1-3µm are much more relevant in this respect. Based on this finding the Symbicort Turbuhaler, Seretide Diskus, Rolenium Elpenhaler and Foster (Fostair) NEXThaler ICS/LABA combination DPIs were tested in vitro as a function of the pressure drop (2, 4 and 6kPa) across the inhaler. Obtained fine particle fractions (FPFs) <5µm (as percent of label claim) were divided into subfractions <1, 1-3 and 3-5µm. Differences of up to a factor of 4 were found between the best (Turbuhaler) and worst performing DPI (Elpenhaler), particularly for the FPF in the size range 1-3µm. The NEXThaler, described as delivering 'extrafine' particles, did not appear to be superior in this size range. The marked differences in amount and size distribution of the aerosols between the devices in this study must cause significant differences in the total lung dose and drug distribution over the airways.

The role of disposable inhalers in pulmonary drug delivery.

INTRODUCTION: There is increasing interest in the pulmonary route for both local and systemically acting drugs, vaccines and diagnostics and new applications may require new inhaler technology to obtain the most therapeutically and/or cost-effective administration. Some of these new applications can benefit from the use of disposable inhalers. AREAS COVERED: Current trends in pulmonary drug delivery are presented in this review as well as the possible contribution of disposable inhalers to the improvement of pulmonary administration therein. Arguments in favour of disposable inhalers and the starting points for development of devices and their formulations are discussed. Also, a brief review of the state of the art regarding current disposable inhaler development is given. EXPERT OPINION: Prerequisites for the use of disposable inhalers, particularly dry powder inhalers, in applications such as childhood vaccination and for preventing or stopping pandemic outbreaks of highly infectious diseases (like influenza, bird flu, SARS) are that they are simple, cheap and effective. Not only do the devices have to be simple in design, but the drug formulations should also be cheap. This may require a different approach as the formulation may not need to be adapted to improve the inhaler must be designed to enhance formulation dispersion.

A novel aerosol generator for homogenous distribution of powder over the lungs after pulmonary administration to small laboratory animals.

To evaluate powder formulations for pulmonary administration in pre-clinic research, the powder should be administered to the lungs of small laboratory animals. To do so properly, a device is needed that generates particles small enough to reach deep into the lungs. In this study a newly developed aerosol generator was tested for pulmonary administration of powder to the lungs of mice and its performance was compared to the only currently available device, the Penn-Century insufflator. Results showed that both devices generated powder particles of approximately the same size distribution, but the fine particle fraction needed for deep lung administration was strongly improved when the aerosol generator was used.Imaging studies in mice showed that powder particles from the aerosol generator deposited into the deep lung, where powder from the Penn-Century insufflator did not reach further than the conducting airways.Furthermore, powder administered by using the aerosol generator was more homogenously distributed over the five individual lungs lobes than powder administrated by using the Penn-Century insufflator.

Effect of inhaler design variables on paediatric use of dry powder inhalers.

Age appropriateness is a major concern of pulmonary delivery devices, in particular of dry powder inhalers (DPIs), since their performance strongly depends on the inspiratory flow manoeuvre of the patient. Previous research on the use of DPIs by children focused mostly on specific DPIs or single inspiratory parameters. In this study, we investigated the requirements for a paediatric DPI more broadly using an instrumented test inhaler. Our primary aim was to assess the impact of airflow resistance on children's inspiratory flow profiles. Additionally, we investigated children's preferences for airflow resistance and mouthpiece design and how these relate to what may be most suitable for them. We tested 98 children (aged 4.7-12.6 years), of whom 91 were able to perform one or more correct inhalations through the test inhaler. We recorded flow profiles at five airflow resistances ranging from 0.025 to 0.055 kPa0.5.min.L-1 and computed various inspiratory flow parameters from these recordings. A sinuscope was used to observe any obstructions in the oral cavity during inhalation. 256 flow profiles were included for analysis. We found that both airflow resistance and the children's characteristics affect the inspiratory parameters. Our data suggest that a medium-high resistance is both suitable for and well appreciated by children aged 5-12 years. High incidences (up to 90%) of obstructions were found, which may restrict the use of DPIs by children. However, an oblong mouthpiece that was preferred the most appeared to positively affect the passageway through the oral cavity. To accommodate children from the age of 5 years onwards, a DPI should deliver a sufficiently high fine particle dose within an inhaled volume of 0.5 L and at a peak inspiratory flow rate of 25-40 L.min-1. We recommend taking these requirements into account for future paediatric inhaler development.

The clinical relevance of dry powder inhaler performance for drug delivery.

BACKGROUND: Although understanding of the scientific basis of aerosol therapy with dry powder inhalers (DPIs) has increased, some misconceptions still persist. These include the beliefs that high resistance inhalers are unsuitable for some patients, that extra fine (<1.0 µm) particles improve peripheral lung deposition and that inhalers with flow rate-independent fine particle fractions (FPFs) produce a more consistent delivered dose to the lungs. OBJECTIVES: This article aims to clarify the complex inter-relationships between inhaler design and resistance, inspiratory flow rate (IFR), FPF, lung deposition and clinical outcomes, as a better understanding may result in a better choice of DPI for individual patients. METHODS: The various factors that determine the delivery of drug particles into the lungs are reviewed. These include aerodynamic particle size distribution, the inspiratory manoeuvre, airway geometry and the three basic principles that determine the site and extent of deposition: inertial impaction, sedimentation and diffusion. DPIs are classed as either dependent or independent of inspiratory flow rate and vary in their internal resistance to inspiration. The effects of these characteristics on drug deposition in the airways are described using data from studies directly comparing currently available inhaler devices. RESULTS: Clinical experience shows that most patients can use a high resistance DPI effectively, even during exacerbations. Particles in the aerodynamic size range from 1.5-5 µm are shown to be optimal, as particles <1.0 µm are very likely to be exhaled again while those >5 µm may impact on the oropharynx. For DPIs with a constant FPF at all flow rates, less of the delivered dose reaches the central and peripheral lung when the flow rate increases, risking under-dosing of the required medication. In contrast, flow rate-dependent inhalers increase their FPF output at higher flow rates, which compensates for the greater impaction on the upper airways as flow rate increases. CONCLUSIONS: The technical characteristics of different inhalers and the delivery and deposition of the fine particle dose to the lungs may be important additional considerations to help the physician to select the most appropriate device for the individual patient to optimise their treatment.

Adenosine dry powder inhalation for bronchial challenge testing, part 2: proof of concept in asthmatic subjects.

Adenosine is an indirect stimulus to assess bronchial hyperresponsiveness (BHR(2)) in asthma. Bronchial challenge tests are usually performed with nebulised solutions of adenosine 5'-monophosphate (AMP(3)). The nebulised AMP test has several disadvantages, like long administration times and a restrictive maximum concentration that does not result in BHR in all patients. In this study, we investigated the applicability of dry powder adenosine for assessment of BHR in comparison to nebulised AMP. Dry powder adenosine was prepared in doubling doses (0.01-80 mg) derived from the nebulised AMP test with addition of two higher doses. Five asthmatic subjects performed two bronchial challenge tests, one with nebulised AMP following the 2-min tidal breathing method; the second with dry powder adenosine administered with an investigational inhaler and single slow inhalations (inspiratory flow rate 30-40 L/min). All subjects reached a 20% fall in FEV1(4) with the new adenosine test (PD20(5)) compared to four subjects with the AMP test (PC20(6)). Dry powder adenosine was well tolerated by all subjects and better appreciated than nebulised AMP. In conclusion, this new bronchial challenge test appears to be a safe and convenient alternative to the nebulised AMP test to assess BHR in asthmatic subjects.

A proposed definition of the 'activity' of surface sites on lactose carriers for dry powder inhalation.

A new definition of the activity of surface sites on lactose carriers for dry powder inhalation is proposed which relates to drug detachment during dispersion. The new definition is expected to improve the understanding of 'carrier surface site activity', which stimulates the unambiguous communication about this subject and may aid in the rational design and interpretation of future formulation studies. In contrast to the currently prevailing view on carrier surface site activity, it follows from the newly proposed definition that carrier surface site activity depends on more variables than just the physicochemical properties of the carrier surface. Because the term 'active sites' is ambiguous, it is recommended to use the term 'highly active sites' instead to denote carrier surface sites with a relatively high activity.

The dispersion behaviour of dry powder inhalation formulations cannot be assessed at a single inhalation flow rate.

The dispersion performances of inhalation powders are often tested at only one inhalation flow rate in mechanistic formulation studies. This limited approach is challenged by studies showing that interactions exist between inhalation flow rate and the effects on dispersion performance of several formulation variables. In this note we explain that such interactions with inhalation flow rate are, in fact, always to be expected. Because these interactions may greatly affect conclusions concerning the effects of formulation variables and their underlying mechanisms, the utility of future dry powder inhalation formulation studies may benefit from an approach in which dispersion performance is by default tested over a range of inhalation flow rates.

New mechanisms to explain the effects of added lactose fines on the dispersion performance of adhesive mixtures for inhalation.

Fine excipient particles or 'fines' have been shown to improve the dispersion performance of carrier-based formulations for dry powder inhalation. Mechanistic formulation studies have focussed mainly on explaining this positive effect. Previous studies have shown that higher drug contents may cause a decrease in dispersion performance, and there is no reason why this should not be true for fines with a similar shape, size and cohesiveness as drug particles. Therefore, the effects on drug detachment of 'fine lactose fines' (FLF, X50 = 1.95 µm) with a similar size and shape as micronised budesonide were studied and compared to those of 'coarse lactose fines' (CLF, X50 = 3.94 µm). Furthermore, interactions with the inhalation flow rate, the drug content and the mixing order were taken into account. The observed effects of FLF are comparable to drug content effects in that the detached drug fraction was decreased at low drug content and low flow rates but increased at higher flow rates. At high drug content the effects of added FLF were negligible. In contrast, CLF resulted in higher detached drug fractions at all flow rates and drug contents. The results from this study suggest that the effects of fines may be explained by two new mechanisms in addition to those previously proposed. Firstly, fines below a certain size may increase the effectiveness of press-on forces or cause the formation of strongly coherent fine particle networks on the carrier surface containing the drug particles. Secondly, when coarse enough, fines may prevent the formation of, or disrupt such fine particle networks, possibly through a lowering of their tensile strength. It is recommended that future mechanistic studies are based on the recognition that added fines may have any effect on dispersion performance, which is determined by the formulation and dispersion conditions.

Adenosine dry powder inhalation for bronchial challenge testing, part 1: inhaler and formulation development and in vitro performance testing.

Dry powder administration of adenosine by use of an effective inhaler may be an interesting alternative to nebulisation of adenosine 5'-monophosphate in bronchial challenge testing, because of a shorter administration time and more consistent delivered fine particle dose over the entire dose range. In this study, we tested various powder formulations and classifier based dispersion principles and investigated the in vitro performance of the most promising formulation/classifier combination in a new test inhaler system. Spray-dried formulations of either pure adenosine (100%) or adenosine and lactose as diluent (1% and 10% adenosine) were prepared to cover the entire expected dose range for adenosine (0.01-20mg). All three powders, in all 12 suggested doses, dispersed well with the newly developed test inhaler with a multiple air jet classifier disperser, into aerosols with an average volume median diameter of 3.1µm (3.0-3.3µm). For eleven out of 12 dose steps, the fine particle fractions<5µm as percent of the loaded dose varied within the range of 67-80% (mean: 74%). The new test concept allows for more consistent aerosol delivery over the entire dose range with narrower size distributions than nebulisation and thus may improve adenosine administration in bronchial challenge testing.

Drug content effects on the dispersion performance of adhesive mixtures for inhalation.

The drug content in adhesive mixtures for inhalation is known to influence their dispersion performance, but the direction and magnitude of this influence depends on other variables. In the past decades several mechanisms have been postulated to explain this finding and a number of possible interacting variables have been identified. Still, the role of drug content in the formulation of adhesive mixtures for inhalation, which includes its significance as an interacting variable to other parameters, is poorly understood. Therefore, the results from a series of drug detachment experiments are presented in which the effect of drug content and its dependence on flow rate, the mixing time and the type of drug is studied. Furthermore, it is investigated whether the effect depends on the range within which the drug content is changed. Quantitative and qualitative multiple order interactions are observed between these variables, which may be explained by a shifting balance between three different mechanisms. The results therefore demonstrate that accounting for (multiple order) interactions between variables has to be part of quality by design activities and the rational design of future experiments.

Devices and formulations for pulmonary vaccination.

INTRODUCTION: Pulmonary vaccination could be a promising alternative to vaccination by injection. Administration of a vaccine to the lungs does not require the use of needles, which reduces the number of trained healthcare workers needed, the risk of needle-stick injuries and needle waste. Besides a systemic immune response, pulmonary vaccination may also induce a mucosal immune response. Such a local response may increase the effectiveness of vaccination against airborne pathogens. Although this route of administration has been studied for decades, no pulmonary vaccine is commercially available yet, due to various challenges mostly intrinsic to pulmonary drug delivery and vaccine formulation. AREAS COVERED: This review discusses the inhalation devices and formulation strategies that may be suitable for the pulmonary administration of vaccines. In addition, critical parameters are addressed, such as the target population, to help assessing whether pulmonary administration of a specific vaccine may be feasible and beneficial or not. EXPERT OPINION: A combined approach of inhalation device and vaccine formulation development is essential. This should result in a system that can effectively be used by the target population and can be produced at low costs. Only then, this challenging administration route can be successfully applied to large-scale vaccination programs.

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.

Characterisation of high dose aerosols from dry powder inhalers.

Developments in high dose dry powder aerosol delivery will increasingly challenge the applicability of currently used aerosol characterisation techniques. With cascade impaction analysis bounce effects can negatively influence stage collection efficiency, especially with increasing impactor loads. In this study the suitability of the multi stage liquid impinger (MSLI) and the Next Generation Impactor (NGI) for the characterisation of dry powder aerosols containing up to 50mg of drug is evaluated. The occurrence of bounce effects is quantitatively assessed by comparison with data obtained from laser diffraction analysis. The liquid based impaction surfaces of the MSLI largely prevent bounce effects, but the low number of cut-off values associated with this impactor hinders accurate data interpretation. With the NGI, a standard high viscosity plate coating insufficiently reduces bounce effects, causing the fraction <1 µm to be higher than what can maximally be expected based on the primary particle size distribution (PSD) obtained from RODOS dispersion. With this type of impactor, the use of solvent soaked filters as impaction surface is necessary to eliminate bounce effects.