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 (<1 μm) particles can improve central and deep lung deposition. Our data show instead that particles in the range 1–3 μm 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 6 kPa) across the inhaler. Obtained fine particle fractions (FPFs) <5 μm (as percent of label claim) were divided into subfractions <1, 1–3 and 3–5 μm. 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 1–3 μm. 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

Comparative in vitro evaluation of four corticosteroid metered dose inhalers:Consistency of delivered dose and particle size distribution

SummaryIntroductionRecent developments concerning pressurized metered dose inhalers (pMDIs) with inhaled corticosteroids (ICS) are the introduction of ciclesonide and the replacement of propellants. As the results of in vivo studies depend on pMDIperformance, it is necessary to evaluate pMDIs in vitro for delivered dose and particle size distributions under different conditions.MethodsFluticasone 125μg, budesonide 200μg, beclomethasone HFA100μg, and ciclesonide 160μg were compared for delivered dose and particle size using laser diffraction analysis with inspiratory flow rates of 10, 20 and 30l/s.ResultsThe volume median diameter of budesonide was 3.5μm, fluticasone 2.8μm, beclomethasone and ciclesonide both 1.9μm. The mouthpiece retention was up to 30% of the nominal dose for beclomethasone and ciclesonide, 11–19% for the other pMDIs. Lifespan, flow rate, and air humidity had no significant influence on particle size distribution. The delivered dose of beclomethasone, budesonide, and ciclesonide remained constant over the lifespan. The delivered dose of fluticasone 125 decreased from 106% to 63%; fluticasone 250 also decreased whereas fluticasone 50 remained constant.ConclusionsThere is a significant difference in median particle size distribution between the different ICS pMDIs. Air humidity and inspiratory flow rate have no significant influence on particle size distribution. Ciclesonide 160 and beclomethasone 100 deliver the largest fine particle fractions of 1.1–3.1μm. The changes in delivered dose during the lifespan for the fluticasone 125 and 250 may have implications for patient care

Powder formulation disintegrating system and method for dry powder

For improving efficiency of the application of medical powder formulations a disintegration means for dry powder inhalers is proposed, comprising a substantially cylindrical air circulation chamber (3) with a height being smaller than its diameter, and at least two air supply channels (2, 9) which enter the chamber (3) as tangents to its cylindrical wall (5) at generally opposite sides of this wall (5), suitable for creating a circular air flow pattern inside the chamber (3), both air channels (2, 9) either having different inlets or alternatively sharing the same inlet which is split up, so as to have one passageway (2) for traversing the dose measuring or dose supplying region of the inhaler for enabling the powder quantity of a single dose dragged into the circulation chamber (3) by air flowing through this passageway (2), and the other passageway to serve as a bypass channel (9) towards the circulation chamber (3) suitable for accelerating the particles and creating a more symmetrical flow pattern inside said chamber (3), and a method

Characterization of inhalation aerosols: a critical evaluation of cascade impactor analysis and laser diffraction technique

Cascade impactor analysis is the standard technique for in vitro characterization of aerosol clouds generated by medical aerosol generators. One important reason for using this inertial separation principle is that drug fractions are classified into aerodynamic size ranges that are relevant to the deposition in the respiratory tract. Measurement of these fractions with chemical detection methods enables establishment of the particle size distribution of the drug in the presence of excipients. However, the technique is laborious and time consuming and most of the devices used for inhaler evaluation lack sufficient possibilities for automation. In addition to that; impactors often have to be operated under conditions for which they were not designed and calibrated. Particularly, flow rates through impactors are increased to values at which the flow through the nozzles is highly turbulent. This has an uncontrolled influence on the collection efficiencies and cut-off curves of these nozzles. Moreover, the cut-off value varies with the flow rate through an impactor nozzle. On the other hand, the high air flow resistances of most impactors are rather restricting to the attainable (fixed) inspiratory flow curves through these devices. Especially for breath actuated dry powder inhalers, higher flow rates and flow increase rates may be desirable than can be achieved in combination with a particular type of impactor. In this paper, the applicability of laser diffraction technology is evaluated as a very fast and highly reliable alternative for cascade impactor analysis. With this technique, aerodynamic diameters cannot be measured, but for comparative evaluation and development, comprising most in vitro applications, this is not necessary. Laser diffraction has excellent possibilities for automated recording of data and testing conditions, and the size classes are independent of the flow rate. Practical limitations can be overcome by using a special inhaler adapter which enables control of the inspiratory flow curve through the inhaler, analysis of the emitted fine particle mass fraction and pre-separation of large particles during testing of dry powder inhalers containing adhesive mixtures. (C) 2002 Elsevier Science B.V. All rights reserved

Are extra-fine particles from dry powder inhalers likely to improve lung deposition?

Rationale: Differences between CFC- and HFA-MDIs include the particle size distribution of the aerosol and the discharge velocity of the aerosol. Because deposition of aerosol particles decreases rapidly in all lung sections with decreasing particle diameter below 1.5 μm, it is questionable whether there is any real advantage from administration of extra-fine particles without the benefit of a low delivery velocity. And although recent reviews have led to the conclusion that there is no convincing evidence yet for increased benefit from the use of extra-fine particles in asthmatic patients, a dry powder inhaler (DPI: Foster NEXThaler) with an extra-fine aerosol output has also now become available. Methods: Fine particle doses (FPDs) from Foster NEXThaler (F-N) measured with the Next Generation Impactor at 2, 4 and 6 kPa were compared with those from Symbicort Turbuhaler (S-TBH), Seretide Diskus (S-D) and Rolenium Elpenhaler (R-E) and evaluated in relation to the corresponding flow rates. Results: Flow rates corresponding with 4 kPa and delivered FPDs as percent of label claim at 4 kPa are summarised in the table. (Figure Presented) Conclusion: The FPD% <1 μm from NEXThaler is much higher than that from the other DPIs. Because this is at about the same flow rate, it is arguable whether this will result in significantly higher lung deposition, as FPD% 1-5 μm from NEXThaler takes an intermediate position between the other DPIs

The rate of drug particle detachment from carrier crystals in an air classifier-based inhaler

Purpose. To investigate the rate with which drug particles are detached from carrier particles in adhesive mixtures when the action of the separation forces during inhalation is sustained by circulation of the powder dose in an air classifier. Methods. Residual drug on retained carrier particles from different adhesive mixture compositions has been analyzed after different circulation times in the classifier (0.5 to 6 s). For calculation of the detachment rate within the first 0.5 s of inhalation, the optical concentration of the aerosol from the classifier has been measured with laser diffraction technique. Results. Drug detachment from carrier crystals during inhalation increases not only with the flow rate but also with the time during which the action of the separation forces (at a constant flow rate) is sustained. The detachment rate at the same flow rate varies with the carrier size fraction and carrier payload and is clearly highest within the first 0.5 s of inhalation. Conclusions. Drug detachment from carrier approaches first-order reaction within the first half-second of inhalation. But at longer circulation times in the classifier, the ratio of removal to adhesive forces decreases dramatically. To increase the detached fraction of drug during inhalation at a constant flow rate, a short residence time for the powder in the de-agglomerator between 0.5 and 2 s is desired. © 2004 Springer Science+Business Media, Inc