Role of agglomeration in the dispersion of salmeterol xinafoate from mixtures for inhalation with differing drug to fine lactose ratios

Microstructural insight into inhalation powder blends through correlative multi-scale X-ray computed tomography

Dry powder inhalers (DPI) are important for topical drug delivery to the lungs, but characterising the pre-aerosolised powder microstructure is a key initial step in understanding the post-aerosolised blend performance. In this work, we characterise the pre-aerosolised 3D microstructure of an inhalation blend using correlative multi-scale X-ray Computed Tomography (XCT), identifying lactose and drug-rich phases at multiple length scales on the same sample. The drug-rich phase distribution across the sample is shown to be homogeneous on a bulk scale but heterogeneous on a particulate scale, with individual clusters containing different amounts of drug-rich phase, and different parts of a carrier particle coated with different amounts of drug-rich phase. Simple scalings of the drug-rich phase thickness with carrier particle size are used to derive the drug-proportion to carrier particle size relationship. This work opens new doors to micro-structural assessment of inhalation powders that could be invaluable for bioequivalence assessment of dry powder inhalers.

Remdesivir Powders Manufactured by Jet Milling for Potential Pulmonary Treatment of COVID-19

Remdesivir is one of the effective drugs proposed for the treatment of coronavirus disease 2019 (COVID-19). However, the study on inhalable regimen is currently limited though COVID-19 is respiratory diseases and infects lung area. This work aims to prepare inhalable remdesivir formulations and verify their effectiveness through in vitro evaluations.Formulations containing different ratios of jet-milled inhalable remdesivir (5%, 10%, 20%,40%,70%) with excipients were produced and characterized in terms of the particle size distribution, particle morphology, flowability, water content, crystallinity, the water sorption and desorption capabilities and the aerodynamic performance.Results indicating that drug loading is a vital factor in facilitating the dispersion of remdesivir dry powder, and the ternary excipient plays a negligible role in improving aerosol performance. Besides, the 70% remdesivir with lactose carrier (70%RD-Lac) was physically stable and retain high aerosol performance after conditioned at 40 °C and 75% RH for a month. Therefore, formulation 70% RD-Lac might be recommended as a candidate product for the potential treatment of COVID-19.

Mixing of dry powders for inhalation: A review

The process of solids mixing is applied across a considerable range of industries. Pharmaceutical science is one of those industries that utilizes solids mixing extensively. Specifically, solids mixing as a key factor in the preparation of dry powder inhalers using the ordered mixing process will be discussed here. This review opens with a history of dry powder mixing theory, continues to ordered mixing in the preparation for dry powder inhalers, details key interparticulate interactions, explains formulation components for dry powder blends, and finally discusses different types of mixers used in the production of dry powder blends for inhalation. Lastly, the authors offer some suggestions for future work on this topic.

Elucidating the Effect of Fine Lactose Ratio on the Rheological Properties and Aerodynamic Behavior of Dry Powder for Inhalation

Dry powder inhaler (DPI) is recognized as the first choice for lung diseases' treatment. However, it lacks a universal way for DPI formulation development. Fine lactose is commonly added in DPIs to improve delivery performance; however, the fine ratio-dependent mechanism is unclear. Therefore, the objective of this study is to explore the influence of fine lactose ratio on DPI powder properties and aerodynamic behavior, and the fine lactose ratio-dependent mechanism involved during powder fluidization and lung deposition. Here salbutamol sulfate was used as a model drug, Lactohale® 206 as coarse carrier, and Lactohale® 300 as fine component; the mixtures were prepared at 1% drug content, with fine content up to 20%. It was shown that with the fine addition, flowability of the mixtures was improved, interaction among particles was increased, and the presence of fines could help to improve DPI's aerosolization performance. When the fines added were less than 3%, the "active site" hypothesis played a leading role. When the added fines were over 3% but less than 10%, fluidization enhancement mechanism was more important. After the added fines reaching 10%, aggregate mechanism started to dominate. However, FPF cannot be further increased once the fines reached 20%. Moreover, the correlations between FPF and dynamic powder parameters were verified in ternary mixtures, and cohesion had a greater impact on FPF than that of flowability. In conclusion, adding lactose fines is an effective way to improve lung deposition of DPI, with the concrete mechanism lactose fine ratio dependent.

Understanding Dry Powder Inhalers: Key Technical and Patient Preference Attributes

Inhalable medications for patients with asthma and chronic obstructive pulmonary disease (COPD) can be confusing even for health care professionals because of the multitude of available devices each with different operating principles. Dry powder inhalers (DPI) are a valuable option for almost all of the patients with asthma or COPD. Based on recorded patient inspiratory profiles, the peak inspiratory flow requirement of 30 L min⁻¹ of high-resistance devices does not usually pose any practical limitations for the patients. Suboptimal adherence and errors in device handling are common and require continuous checking and patient education in order to avoid these pitfalls of all inhalation therapy. The aim of this opinion paper is to describe the working principles of DPIs and to summarise their key properties in order to help prescribing the correct inhaler for each patient.

Funding: Orion Pharma.

Agglomerated novel spray-dried lactose-leucine tailored as a carrier to enhance the aerosolization performance of salbutamol sulfate from DPI formulations

Spray-drying allows to modify the physicochemical/mechanical properties of particles along with their morphology. In the present study, _L-leucine with varying concentrations (0.1, 0.5, 1, 5, and 10% w/v) were incorporated into lactose monohydrate solution for spray-drying to enhance the aerosolization performance of dry powder inhalers containing spray-dried lactose-leucine and salbutamol sulfate. The prepared spray-dried lactose-leucine carriers were analyzed using laser diffraction (particle size), differential scanning calorimetry (thermal behavior), scanning electron microscopy (morphology), powder X-ray diffraction (crystallinity), Fourier transform infrared spectroscopy (interaction at molecular level), and in vitro aerosolization performance (deposition). The results showed that the efficacy of salbutamol sulfate’s aerosolization performance was, in part, due to the introduction of _L-leucine in the carrier, prior to being spray-dried, accounting for an increase in the fine particle fraction (FPF) of salbutamol sulfate from spray-dried lactose-leucine (0.5% leucine) in comparison to all other carriers. It was shown that all of the spray-dried carriers were spherical in their morphology with some agglomerates and contained a mixture of amorphous, α-lactose, and β-lactose. It was also interesting to note that spray-dried lactose-leucine particles were agglomerated during the spray-drying process to make coarse particles (volume mean diameter of 79 to 87 μm) suitable as a carrier in DPI formulations.

Improving Dry Powder Inhaler Performance by Surface Roughening of Lactose Carrier Particles

PURPOSE

This study investigated the impact of macro-scale carrier surface roughness on the performance of dry powder inhaler (DPI) formulations.

METHODS

Fluid-bed processing and roller compaction were explored as processing methods to increase the surface roughness (Ra) of lactose carrier particles. DPI formulations containing either (a) different concentrations of fine lactose at a fixed concentration of micronized drug (isoniazid) or (b) various concentrations of drug in the absence of fine lactose were prepared. The fine particle fraction (FPF) and aerodynamic particle size of micronized drug of all formulations were determined using the Next Generation Impactor.

RESULTS

Fluid-bed processing resulted in a modest increase in the Ra from 562 to 907 nm while roller compaction led to significant increases in Ra > 1300 nm. The roller compacted carriers exhibited FPF > 35%, which were twice that of the smoothest carriers. The addition of up to 5%, w/w of fine lactose improved the FPF of smoother carriers by 60-200% whereas only < 30% increase was observed in the rough carriers. Analysis of the FPF in tandem with shifts in the mass median aerodynamic diameter of dispersed drug suggested that the finest drug particles were entrapped on rougher surfaces while larger drug particles were dispersed in the air.

CONCLUSIONS

The results showed that the processing of lactose carrier particles by roller compaction was immensely beneficial to improving DPI performance, primarily due to increased surface roughness at the macro-scale.

Formulating powder-device combinations for salmeterol xinafoate dry powder inhalers

Using salmeterol xinafoate (SX) as an active pharmaceutical ingredient, the effects of carrier lactose particle type, total lactose fines content and device resistance on dry powder inhaler performance were investigated in vitro. To mimic drug levels in commercial preparations, interactive mixtures containing 0.58% w/w SX were prepared by low shear tumble mixing. Three types of milled inhalation grade lactose were used (Lactohale(®) LH 200, Respitose(®) ML006 and ML001) and the concentration of fine lactose (Lactohale(®) 300) added was varied. The in vitro deposition of each mixture was studied using a next generation impactor and inhaler devices exhibiting different resistances, Rotahaler(®)<Aerolizer(®)<Handihaler(®). Aerosol performance was evaluated based on the emitted dose (ED), mass median aerodynamic diameter (MMAD) ± geometric standard deviation (GSD) and fine particle fraction (FPF). Increases of up to eight-fold in FPF were observed with increasing intrinsic fine lactose content. The addition of extra fine lactose increased the FPF further, although the effect diminished as more fines were added. The Aerolizer produced the best aerosol performance with any given powder blend, although suitable formulations were identified for each device as defined by the a priori success criteria: >80% ED and MMAD ± GSD between 1-5 μm. The results confirmed the factors under investigation to be important determinants of product performance, but demonstrated using realistic conditions how individual factor impact may be enhanced or mitigated by inter-dependency.

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.

Physico-chemical aspects of lactose for inhalation

A dry powder inhaler (DPI) is a dosage form that consists of a powder formulation in a device which is designed to deliver an active ingredient to the respiratory tract. It has been extensively investigated over the past years and several aspects relating to device and particulate delivery mechanisms have been the focal points for debate. DPI formulations may or may not contain carrier particles but whenever a carrier is included in a commercial formulation, it is almost invariably lactose monohydrate. Many physicochemical properties of the lactose carrier particles have been reported to affect the efficiency of a DPI. A number of preparation methods have been developed which have been claimed to produce lactose carriers with characteristics which lead to improved deposition. Alongside these developments, a number of characterization methods have been developed which have been reported to be useful in the measurement of key properties of the particulate ingredients. This review describes the various physicochemical characteristics of lactose, methods of manufacturing lactose particulates and their characterization.

Lactose characteristics and the generation of the aerosol

The delivery efficiency of dry-powder products for inhalation is dependent upon the drug formulation, the inhaler device, and the inhalation technique. Dry powder formulations are generally produced by mixing the micronised drug particles with larger carrier particles. These carrier particles are commonly lactose. The aerosol performance of a powder is highly dependent on the lactose characteristics, such as particle size distribution and shape and surface properties. Because lactose is the main component in these formulations, its selection is a crucial determinant of drug deposition into the lung, as interparticle forces may be affected by the carrier-particle properties. Therefore, the purpose of this article is to review the various grades of lactose, their production, and the methods of their characterisation. The origin of their adhesive and cohesive forces and their influence on aerosol generation are described, and the impact of the physicochemical properties of lactose on carrier-drug dispersion is discussed in detail.

Dry powder aerosols generated by standardized entrainment tubes from drug blends with lactose monohydrate: 1. Albuterol sulfate and disodium cromoglycate

The major objective of this study was: discriminatory assessment of dry powder aerosol performance using standardized entrainment tubes (SETs) and lactose-based formulations with two model drugs. Drug/lactose interactive physical mixtures (2%w/w) were prepared. Their properties were measured: solid-state characterization of phase behavior and molecular interactions by differential scanning calorimetry and X-ray powder diffraction; particle morphology and size by scanning electron microscopy and laser diffraction; aerosol generation by SETs and characterization by twin-stage liquid impinger and Andersen cascade impactor operated at 60 L/min. The fine particle fraction (FPF) was correlated with SET shear stress (tau(s)), using a novel powder aerosol deaggregation equation (PADE). Drug particles were <5 microm in volume diameter with narrow unimodal distribution (Span <1). The lowest shear SET (tau(s) = 0.624 N/m(2)) gave a higher emitted dose (ED approximately 84-93%) and lower FPF (FPF(6.4) approximately 7-25%). In contrast, the highest shear SET (tau(s) = 13.143 N/m(2)) gave a lower ED (ED approximately 75-89%) and higher FPF (FPF(6.4) approximately 15-46%). The performance of disodium cromoglycate was superior to albuterol sulfate at given tau(s), as was milled with respect to sieved lactose monohydrate. Excellent correlation was observed (R(2) approximately 0.9804-0.9998) when pulmonary drug particle release from the surface of lactose carriers was interpreted by PADE linear regression for dry powder formulation evaluation and performance prediction.

Influence of the polydispersity of the added fine lactose on the dispersion of salmeterol xinafoate from mixtures for inhalation

The purpose of this study was to determine and understand the effect of the polydispersity of fine lactose (FL) on the dispersion of salmeterol xinafoate (SX) from SX-coarse lactose mixtures for inhalation. SX mixtures were prepared using validated laboratory mixing. The in vitro deposition of SX was measured using a twin-stage impinger and SX analysed using high performance liquid chromatography. The distributions of FL included both cohesive to non-cohesive fractions. Reduction in the span of the FL distributions with a volume median diameters (VMD) about 7 microm showed no significant difference in the fine particle fraction (FPF) of SX (P > 0.05), while reduced FPF of SX was observed with the reduction in the span of FL with VMD about 19 and 32 microm, respectively. When the FPF of SX was correlated with the concentration of FL in specific fractions, there was a marked, linear increase in FPF for increasing concentrations of FL in the 5-10 microm fraction; however, all other fractions showed no significant increase in FPF. The study reflects the importance of lactose polydispersity in drug dispersion. Specific size fractions of cohesive FL enhance dispersion, while non-cohesive fractions of FL act as secondary carriers and decrease dispersion performance.