Structural influence of cohesive mixtures of salbutamol sulphate and lactose on aerosolisation and de-agglomeration behaviour under dynamic conditions

A New Role of Fine Excipient Materials in Carrier-Based Dry Powder Inhalation Mixtures: Effect on Deagglomeration of Drug Particles During Mixing Revealed

The potential of fine excipient materials to improve the performance of carrier-based dry powder inhalation mixtures is well acknowledged. The mechanisms underlying this potential are, however, open to question till date. Elaborate understanding of these mechanisms is a requisite for rational rather than empirical development of ternary dry powder inhalation mixtures. While effects of fine excipient materials on drug adhesion to and detachment from surfaces of carrier particle have been extensively investigated, effects on other processes, such as carrier-drug mixing, capsule/blister/device filling, or aerosolization in inhaler devices, have received little attention. We investigated the influence of fine excipient materials on the outcome of the carrier-drug mixing process. We studied the dispersibility of micronized fluticasone propionate particles after mixing with α-lactose monohydrate blends comprising different fine particle concentrations. Increasing the fine (D < 10.0 μm) excipient fraction from 1.84 to 8.70% v/v increased the respirable drug fraction in the excipient-drug mixture from 56.42 to 67.80% v/v (p < 0.05). The results suggest that low concentrations of fine excipient particles bind to active sites on and fill deep crevices in coarse carrier particles. As the concentration of fine excipient particles increases beyond that saturating active sites, they fill the spaces between and adhere to the surfaces of coarse carrier particles, creating projections and micropores. They thereby promote deagglomeration of drug particles during carrier-drug mixing. The findings pave the way for a comprehensive understanding of contributions of fine excipient materials to the performance of carrier-based dry powder inhalation mixtures.

Investigation into the Manufacture and Properties of Inhalable High-Dose Dry Powders Produced by Comilling API and Lactose with Magnesium Stearate

The aim of the study was to understand the impact of different concentrations of the additive material, magnesium stearate (MGST), and the active pharmaceutical ingredient (API), respectively, on the physicochemical properties and aerosol performance of comilled formulations for high-dose delivery. Initially, blends of API/lactose with different concentrations of MGST (1-7.5% w/w) were prepared and comilled by the jet-mill apparatus. The optimal concentration of MGST in comilled formulations was investigated, specifically for agglomerate structure and strength, particle size, uniformity of content, surface coverage, and aerosol performance. Secondly, comilled formulations with different API (1-40% w/w) concentrations were prepared and similarly analyzed. Comilled 5% MGST (w/w) formulation resulted in a significant improvement in in vitro aerosol performance due to the reduction in agglomerate size and strength compared to the formulation comilled without MGST. Higher concentrations of MGST (7.5% w/w) led to reduction in aerosol performance likely due to excessive surface coverage of the micronized particles by MGST, which led to failure in uniformity of content and an increase in agglomerate strength and size. Generally, comilled formulations with higher concentrations of API increased the agglomerate strength and size, which subsequently caused a reduction in aerosol performance. High-dose delivery was achieved at API concentration of >20% (w/w). The study provided a platform for the investigation of aerosol performance and physicochemical properties of other API and additive materials in comilled formulations for the emerging field of high-dose delivery by dry powder inhalation.

Large porous particles for respiratory drug delivery. Glycine-based formulations

Large porous particles are becoming increasingly popular as carriers for pulmonary drug delivery with both local and systemic applications. These particles have high geometric diameters (5-30μm) but low bulk density (~0.1g/cm³ or less) such that the aerodynamic diameter remains low (1-5μm). In this study salbutamol and budesonide serve as model inhalable drugs with poor water solubility. A novel method is proposed for the production of dry powder inhaler formulations with enhanced aerosol performance (e.g. for salbutamol-glycine formulation the fine particle fraction (FPF≤4.7μm) value is 67.0±1.3%) from substances that are poorly soluble in water. To overcome the problems related to extremely poor aqueous solubility of the APIs, not individual solvents are used for spray freeze-drying of API solutions, but organic-water mixtures, which can form clathrate hydrates at low temperatures and release APIs or their complexes as fine powders, which form large porous particles after the clathrates are removed by sublimation. Zwitterionic glycine has been used as an additive to API directly in solutions prior to spray freeze-drying, in order to prevent aggregation of powders, to enhance their dispersibility and improve air-flow properties. The clathrate-forming spray freeze-drying process in the multi-component system was optimized using low-temperature powder X-ray diffraction and thermal analysis.

Evidence for the existence of powder sub-populations in micronized materials: aerodynamic size-fractions of aerosolized powders possess distinct physicochemical properties

Purpose

To investigate the agglomeration behaviour of the fine (<5.0 μm) and coarse (>12.8 μm) particle fractions of salmeterol xinafoate (SX) and fluticasone propionate (FP) by isolating aerodynamic size fractions and characterising their physicochemical and re-dispersal properties.

Methods

Aerodynamic fractionation was conducted using the Next Generation Impactor (NGI). Re-crystallized control particles, unfractionated and fractionated materials were characterized for particle size, morphology, crystallinity and surface energy. Re-dispersal of the particles was assessed using dry dispersion laser diffraction and NGI analysis.

Results

Aerosolized SX and FP particles deposited in the NGI as agglomerates of consistent particle/agglomerate morphology. SX particles depositing on Stages 3 and 5 had higher total surface energy than unfractionated SX, with Stage 5 particles showing the greatest surface energy heterogeneity. FP fractions had comparable surface energy distributions and bulk crystallinity but differences in surface chemistry. SX fractions demonstrated higher bulk disorder than unfractionated and re-crystallized particles. Upon aerosolization, the fractions differed in their intrinsic emission and dispersion into a fine particle fraction (<5.0 μm).

Conclusions

Micronized powders consisted of sub-populations of particles displaying distinct physicochemical and powder dispersal properties compared to the unfractionated bulk material. This may have implications for the efficiency of inhaled drug delivery.

Development of a high efficiency dry powder inhaler: effects of capsule chamber design and inhaler surface modifications

PURPOSE

The objective of this study was to explore the performance of a high efficiency dry powder inhaler (DPI) intended for excipient enhanced growth (EEG) aerosol delivery based on changes to the capsule orientation and surface modifications of the capsule and device.

METHODS

DPIs were constructed by combining newly designed capsule chambers (CC) with a previously developed three-dimensional (3D) rod array for particle deagglomeration and a previously optimized EEG formulation. The new CCs oriented the capsule perpendicular to the incoming airflow and were analyzed for different air inlets at a constant pressure drop across the device. Modifications to the inhaler and capsule surfaces included use of metal dispersion rods and surface coatings. Aerosolization performance of the new DPIs was evaluated and compared with commercial devices.

RESULTS

The proposed capsule orientation and motion pattern increased capsule vibrational frequency and reduced the aerosol MMAD compared with commercial/modified DPIs. The use of metal rods in the 3D array further improved inhaler performance. Coating the inhaler and capsule with PTFE significantly increased emitted dose (ED) from the optimized DPI.

CONCLUSIONS

High efficiency performance is achieved for EEG delivery with the optimized DPI device and formulation combination producing an aerosol with MMAD < 1.5 μm, FPF<5 μm/ED > 90%, and ED > 80%.

Rapid characterisation of the inherent dispersibility of respirable powders using dry dispersion laser diffraction

Understanding and controlling powder de-agglomeration is of great importance in the development of dry powder inhaler (DPI) products. Dry dispersion laser diffraction measures particle size readily under controlled dispersing conditions, but has not been exploited fully to characterise inherent powder dispersibility. The aim of the study was to utilise particle size-dispersing pressure titration curves to characterise powder cohesivity and ease of de-agglomeration. Seven inhaled drug/excipient powders (beclometasone dipropionate, budesonide, fluticasone propionate, lactohale 300, salbutamol base, salmeterol xinafoate and tofimilast) were subjected to a range of dispersing pressures (0.2-4.5 Bar) in the Sympatec HELOS/RODOS laser diffractometer and particle size measurements were recorded. Particle size-primary pressure data were used to determine the pressures required for complete de-agglomeration. The latter were employed as an index of the cohesive strength of the powder (critical primary pressure; CPP), and the curves were modelled empirically to derive the pressure required for 50% de-agglomeration (DA₅₀). The powders presented a range of CPP (1.0-3.5 Bar) and DA₅₀ (0.23-1.45 Bar) which appeared to be characteristic for different mechanisms of powder de-agglomeration. This approach has utility as a rapid pre-formulation tool to measure inherent powder dispersibility, in order to direct the development strategy of DPI products.

The kinetics of cohesive powder de-agglomeration from three inhaler devices

PURPOSE

The purpose of the current investigation is to understand the kinetics of de-agglomeration (k(d)) of micronised salbutamol sulphate (SS) and lactohale 300 (LH300) under varying air flow rates (30-180l min(-1)) from three dry powder inhaler devices (DPIs), Rotahaler (RH), Monodose Inhaler (MI) and Handihaler (HH).

RESULTS

Cumulative fine particle mass vs. time profiles were obtained from the powder concentration, emitted mass and volume percent <5.4 μm, embedded in the particle size distributions of the aerosol at specific times. The rate of de-agglomeration (k(d)), estimated from non-linear least squares modelling, increased with increasing air flow rates. The k(d)vs. air flow rate profiles of SS and LH300 were significantly different at high air flow rates. The k(d) was highest from RH and lowest from MI. Differences in k(d) between the devices were related to device mode of operation while the differences between the materials were due to the powder bed structure.

CONCLUSION

This approach provided a methodology to measure the rate constant for cohesive powder de-agglomeration following aerosolisation from commercial devices and an initial understanding of the influence of device, air flow rate and material on these rate constants.