On the effects of blending, physicochemical properties, and their interactions on the performance of carrier-based dry powders for inhalation - A review

Elucidating mixing process effects on pulmonary delivery efficiency of dry powder inhalers: A dual-dimensional macroscopic and microscopic perspective

Dry powder inhalers (DPIs) have been widely recommended in lung diseases on account of direct pulmonary delivery, desired drug stability, and satisfactory patient compliance. More than 90% of DPIs products consist of micronized drugs mixed with larger carrier particles for required dose delivery uniformity and desired pulmonary delivery efficiency. In formulation development, researchers often focus on the influence of mixing process on the macroscopic quantitative results of pulmonary drug delivery efficiency. However, the critical influence and underlying modulatory mechanisms of mixing parameters remain poorly understood, posing formidable challenges to the optimization of DPI formulations. In the present study, an internationally recognized cascade impactor method was employed to investigate the effects of mixing parameters on the ultimate pulmonary drug delivery efficiency from a macroscopic perspective. Subsequently, Confocal Microscopic Raman Spectroscopy (CMRS) was applied to innovatively investigate the material distribution and adhesive status of the mixed DPI particles. Meanwhile, the self-constructed Modular Process Analysis Platform (MPAP) was employed the detached behavior during pulmonary delivery, allowing us to explore the influence mechanisms from a microscopic perspective. Ultimately, correlations were established between the mixing parameters and the drug adhesive status, pulmonary drug delivery process and efficiency. This study was expected to provide novelty pioneering paradigms and dual-dimensional perspective for the direction development and optimization of DPIs.

Inhalable Metal-Organic Frameworks: A Promising Delivery Platform for Pulmonary Diseases Treatment

Inhalation delivery, offering a direct pathway for administering drugs to the lungs in the form of dry powders or aerosols, stands out as an optimal approach for the localized treatment of pulmonary diseases. However, the intricate anatomical architecture of the lung often poses challenges in maintaining effective drug concentrations within the lungs over extended periods. This highlights the pressing need to develop rational inhalable drug delivery systems that can improve treatment outcomes for respiratory diseases. Metal-organic frameworks (MOFs) assembled from inorganic metal ions and organic ligands, characterized by customizable porous architecture and chemical composition, modifiable porosity, vast surface area, straightforward surface modification, and adjustable biocompatibility, have garnered extensive attention in the biomedical sphere. The introduction of MOFs into inhalation therapy represents a promising avenue to navigate past the hurdles associated with traditional inhalation methods. Therefore, this review summarizes the characteristics of inhalation delivery together with the latest advances, challenges, and opportunities in utilizing inhalable MOFs for treating lung diseases and discusses prospects in this field alongside the potential pathways for translating this strategy into clinic.

New theory to explain the effect of lactose fines on the performance of adhesive mixtures for inhalation

A new theory for the dispersibility enhancing effect of excipient fines for adhesive mixtures for inhalation is presented in this paper, while at the same time the shortcomings of current hypotheses are discussed. The proposed mechanism, denoted the 'viscoelastic damping effect', states that the presence of fines particles acts to dampen the collisions between carrier particles during mixing. As a consequence, fewer fine particles are 'irreversibly' pressed into the carriers, which in turn entails a higher fine particle fraction. The mechanism was demonstrated experimentally at different levels of added lactose fines by studying the influence of processing on fine particle fraction. This approach furthermore enabled quantification of the effect. All fine particles present in the blend (APIs and excipient fines) act together to exert the damping effect. The proposed mechanism is able to explain the main body of published data, including the effect of added excipient fines, the effect of an increased drug load, and the effect of removal of carrier fines. The viscoelastic damping mechanism is general in nature and conveys a broader and more general understanding of the behavior of adhesive mixtures for inhalation.

A Review on Micro and Nanoengineering in Powder-Based Pulmonary Drug Delivery

Pulmonary delivery of drugs has emerged as a promising approach for the treatment of both lung and systemic diseases. Compared to other drug delivery routes, inhalation offers numerous advantages including high targeting, fewer side effects, and a huge surface area for drug absorption. However, the deposition of drugs in the lungs can be limited by lung defence mechanisms such as mucociliary and macrophages' clearance. Among the delivery devices, dry powder inhalers represent the optimal choice due to their stability, ease of use, and absence of propellants. In the last decades, several bottom-up techniques have emerged over traditional milling to produce inhalable powders. Among these techniques, the most employed ones are spray drying, supercritical fluid technology, spray freeze-drying, and thin film freezing. Inhalable dry powders can be constituted by micronized drugs attached to a coarse carrier (e.g., lactose) or drugs embedded into a micro- or nanoparticle. Particulate-based formulations are commonly composed of polymeric micro- and nanoparticles, liposomes, solid lipid nanoparticles, dendrimers, nanocrystals, extracellular vesicles, and inorganic nanoparticles. Moreover, engineered formulations including large porous particles, swellable microparticles, nano-in-microparticles, and effervescent nanoparticles have been developed. Particle engineering has also a crucial role in tuning the physical-chemical properties of both carrier-based and carrier-free inhalable powders. This approach can increase powder flowability, deposition, and targeting by customising particle surface features.

Fine excipient materials in carrier-based dry powder inhalation formulations: The interplay of particle size and concentration effects

The contributions of fine excipient materials to drug dispersibility from carrier-based dry powder inhalation (DPI) formulations are well recognized, although they are not completely understood. To improve the understanding of these contributions, we investigated the influences of the particle size of the fine excipient materials on characteristics of carrier-based DPI formulations. We studied two particle size grades of silica microspheres, with volume median diameters of 3.31 μm and 8.14 μm, as fine excipient materials. Inhalation formulations, each composed of a lactose carrier material, one of the fine excipient materials (2.5% or 15.0% w/w), and a drug (fluticasone propionate) material (1.5% w/w) were prepared. The physical microstructure, the rheological properties, the aerosolization pattern, and the aerodynamic performance of the formulations were studied. At low concentration, the large silica microspheres had a more beneficial influence on the drug dispersibility than the small silica microspheres. At high concentration, only the small silica microspheres had a beneficial influence on the drug dispersibility. The results reveal influences of fine excipient materials on mixing mechanics. At low concentration, the fine particles improved deaggregation and distribution of the drug particles over the surfaces of the carrier particles. The large silica microspheres were associated with a greater mixing energy and a greater improvement in the drug dispersibility than the small silica microspheres. At high concentration, the large silica microspheres kneaded the drug particles onto the surfaces of the carrier particles and thus impaired the drug dispersibility. As a critical attribute of fine excipient materials in carrier-based dry powder inhalation formulations, the particle size demands robust specification setting.

General aspects of powder rheology applied to pharmaceutical formulations

Powder flowability is crucial in the pharmaceutical industry, strongly affecting solid dosage processing. Classical experimental techniques offer straightforward results for the rapid screening of formulations during development. However, they fail to describe powder properties under consolidation. Complex techniques, such as shear cell, accurately assess fundamental properties of particulate samples under realistic conditions, enabling prediction of their flow. Ideally, a combination of experimental methods should be used to comprehensively assess powder flowability, ensuring consistent product performance. Moreover, researchers and analytical scientists must have a solid understanding of powder rheology to effectively interpret acquired data. In this review, common techniques, experimental protocols, and typical results observed in a pharmaceutical context are described.

Mixing energy as an adjustment tool for aerodynamic behaviour of an inhaled product: In-vitro and in-vivo effects

This paper describes the development of a fixed dose dry powder combination of indacaterol maleate (Inda) and glycopyrronium bromide (Glyco) in Easyhaler® inhaler for a comparative pharmacokinetic (PK) study, as well as the outcome of such a study. The development aim was to produce formulations with three different in vitro dispersibility profiles for both Inda and Glyco. This so-called 'rake' approach allows for quantitation of the candidate formulations relative to the reference product Ultibro® Breezhaler® in terms of the key PK parameters. Three formulations (A, B and C) were produced based on the mixing energy concept. For both APIs, formulation A (lowest mixing energy) displayed the highest fine particle fractions and formulation C (highest mixing energy) the lowest. GMP manufacturing confirmed the performance of the three formulations. The candidate formulations were tested against the reference product in a single dose PK study in healthy volunteers. Clear differences in Inda plasma concentration profiles were observed between the treatments when administered concomitantly with charcoal, with Easyhaler A showing the highest Cmax value and Easyhaler C the lowest. Easyhaler B was bioequivalent to Ultibro Breezhaler with regard to the primary PK parameters of Inda, Cmax and AUC72h. For Glyco, Easyhaler formulations A, B and C provided lower peak concentrations than Ultibro Breezhaler. For AUC72h of Glyco, Easyhaler B was bioequivalent to the reference product. Additional measures for adjustment of formulation performance can be foreseen, whose effects can be predicted based on mixing energy theory.

The effect of mixing on the dispersibility of adhesive mixtures for inhalation. Comparison of high shear and Turbula mixers

This study investigates the effect of different mixers and the applicability of the mixing energy (ME) concept to dry powder formulations for inhalation. With the aim to step-wise build and expand this concept, adhesive mixtures of 2 % budesonide and lactose carrier were investigated, both with 1 % magnesium stearate (MgSt) added in a 'coating' step, and without, the latter referred to as 'naked' formulations. For high shear mixed formulations, the fine particle fraction (FPF) was found to increase with increasing ME up to 60 % and thereafter decreased, using the Novolizer device. The data could be well fitted to the modeling equation, thus confirming the validity of the ME concept. The naked formulations displayed a linear decrease in FPF with increasing ME, again showing the validity of the ME concept. For Turbula mixed formulations, FPF increased with increased mixing time (and mixing energy) for all batches. The naked (binary) composition reached to higher FPF values than for high shear mixing and the formulation with MgSt reached to FPF values around 60 %, demonstrating that it is possible to achieve the same high drug dispersibility with the Turbula mixer as for high shear mixer. An equation for calculation of mixing energy in Turbula mixing was set up in an analogous way to the equation for high shear mixing, which enabled direct comparison between the two mixers.

Recent developments in lactose blend formulations for carrier-based dry powder inhalation

Lactose is the most commonly used excipient in carrier-based dry powder inhalation (DPI) formulations. Numerous inhalation therapies have been developed using lactose as a carrier material. Several theories have described the role of carriers in DPI formulations. Although these theories are valuable, each DPI formulation is unique and are not described by any single theory. For each new formulation, a specific development trajectory is required, and the versatility of lactose can be exploited to optimize each formulation. In this review, recent developments in lactose-based DPI formulations are discussed. The effects of varying the material properties of lactose carrier particles, such as particle size, shape, and morphology are reviewed. Owing to the complex interactions between the particles in a formulation, processing adhesive mixtures of lactose with the active ingredient is crucial. Therefore, blending and filling processes for DPI formulations are also reviewed. While the role of ternary agents, such as magnesium stearate, has increased, lactose remains the excipient of choice in carrier-based DPI formulations. Therefore, new developments in lactose-based DPI formulations are crucial in the optimization of inhalable medicine performance.

Elucidation of lactose fine size and drug shape on rheological properties and aerodynamic behavior of dry powders for inhalation

Pulmonary drug delivery has gained great attention in local or systemic diseases therapy, however it is still difficult to scale-up DPI production due to the complexity of interactions taking place in DPI systems and limited understanding between flowability and inter-particle interactions in DPI formulations. Therefore, finding some quantitative parameters related to DPI delivery performance for predicting the in vitro drug deposition behavior is essential. Therefore, this study introduces a potential model for predicting aerodynamic performance of carrier-based DPIs, as well to find more relevant fine powder size and optimal shape to improve aerodynamic performance. Using salbutamol sulfate as a model drug, Lactohale®206 as coarse carrier, Lactohale®300, Lactohale®230, and Lactohale®210 as third fine components individually, the mixtures were prepared at 1% (w/w) drug content accompanied with carriers and the third component (ranging from 3 - 7%), influence of lactose fines size on DPI formulation's rheological and aerodynamic properties was investigated. The optimum drug particle shape was also confirmed by computer fluid dynamics model. This study proved that pulmonary deposition efficiency could be improved by decreasing lactose fines size. Only fines in the size range of 0-11 μm have a good linear relationship with FPF, attributed to the fluidization energy enhancement and aggregates mechanism. Once exceeding 11 μm, fine lactose would act as a second carrier, with increased drug adhesion. Computational fluid dynamics (CFD) models indicated fibrous drug particles were beneficial to transfer to the deep lung. Furthermore, good correlations between rheological parameters and FPF of ternary mixtures with different lactose fines were established, and it was disclosed that the FPF was more dependent on interaction parameters than that of flowability.

Effect of pressure drop on the in vitro dispersion of adhesive mixtures of different blend states for inhalation

In this study, the effect of pressure drop (ΔP) on the in vitro dispersion of a series of carrier-based adhesive mixtures of different fines-to-carrier proportions, corresponding to the four different blend states of the blend state model, i.e. S1 to S3, was investigated. Four binary and one ternary adhesive mixture consisting of lactose carrier and budesonide fines and lactose fines were prepared. The dispersion was assessed using a next generation impactor (NGI) at ΔP of 0.5, 2 and 4 kPa. For the S1 mixture, where the fines were located in surface cavities of the carrier, the fine particle fraction (FPF) increased nearly linearly with ΔP. For S2 and S3 mixtures, with adhesion layers on the enveloped carrier surface, the FPF-ΔP relationships were bended and approached a plateau. Examination of powder captured in the pre-separator of the NGI led to the conclusion that the dispersion of these adhesive mixtures occurred by erosion of the adhesion layer, i.e. budesonide was liberated as single particles or micro-agglomerates. It is concluded that the FPF-ΔP relationships were dependent on the blend state and for the S2 and S3 mixtures, a critical pressure drop was identified above which the pressure drop had a limited effect on the FPF.

Insights into the potential of rheological measurements in development of dry powder inhalation formulations

Study of flow is a key to development of dry powder inhalation formulations. Various static (bulk) and dynamic rheological measurements are used to study different aspects of powder flow and packing. Among rheological measurements, the permeability and the fluidization energy are, conceptually, most relevant to dispersion of dry powder inhalation formulations. The aim of the current study was to test the robustness and the range of applications of the two measurements, among other rheological measurements. To this end, we prepared and studied a series of ternary, carrier-based dry powder inhalation formulations. The formulations were mixtures of coarse-fine excipient (α-lactose monohydrate) blends, with different fine excipient concentrations (0.0-15.0 % w/w), and a spray-dried drug (fluticasone propionate) material. The excipient blends were characterized in terms of morphology, size, crystallinity and rheological properties. The formulations were evaluated in vitro using a low resistance inhalation device, the Cyclohaler®, and a high resistance inhalation device, the Handihaler®. The study design aimed to complement literature data. Bulk rheological measurements, specifically the bulk density, the compressibility, and the permeability, exhibited satisfactory precision and could demonstrate changes in powder composition and structure. They hold a potential for use as critical material attributes to aid monitoring and optimization of carrier-based dry powder inhalation formulations in quality-by-design systems. On the other hand, dynamic rheological measurements, specifically the basic flowability energy, the specific energy, and the fluidization energy, generally exhibited high variability, which obscured interpretation of the measurements and implied heterogeneous powder structures. The fluidization energy could, nevertheless, convey structural changes taking place during powder fluidization.

Dry powder inhaler formulation comparison: Study of the role of particle deposition pattern and dissolution

The composition, morphology and dissolution profile of particles and micro-sized agglomerates delivered upon inhalation may have a significant impact on the product clinical effect. However, although several efforts are ongoing, a methodology that considers deposition structures and dissolution performance evaluation in a biorelevant set-up is not yet standardized. The goal of this work is to apply a collection and dissolution methodology able to discriminate dry powder inhaler (DPI) formulations in terms of deposition structures and dissolution profile in vitro. Hence, Fluticasone Propionate (FP) engineered particles and formulated products (used as a case study) were collected employing a breath simulator and characterized regarding (i) aerodynamic particle size distribution; (ii) deposited microstructures; and (iii) dissolution/absorption profiles using the DissolvIt® bio-relevant dissolution equipment. The results indicated that the particle engineering technology had an impact on the generated and deposited microstructures, here associated to the differences on surface properties of jet milled and wet polished particles quantified by the specific surface area. Differences on surface properties modulate particle interactions, resulting in agglomerates of drug substance and excipient upon actuation with significant different morphologies, observed by microscope, as well as quantified by Marple cascade impactor. These observations allow for a further understanding of the DPI aerosolization and deposition mechanisms. The dissolution and absorption assessment indicates that the presence of lactose may accelerate the drug substance dissolution kinetics, and the FP dissolution can be significantly enhanced when formulated as a spray-dried dispersion particle. Ultimately, the results suggest dissolution testing can be an essential tool to both optimize an innovator DPI and de-risk generics development.

A quantitative approach to predicting lung deposition profiles of pharmaceutical powder aerosols

Dry powder inhalers (DPI) are widely used systems for pulmonary delivery of therapeutics. The inhalation performance of DPIs is influenced by formulation features, inhaler device and inhalation pattern. The current review presents the affecting factors with great focus on powder characteristics which include particle size, shape, surface, density, hygroscopicity and crystallinity. The properties of a formulation are greatly influenced by a number of physicochemical factors of drug and added excipients. Since available particle engineering techniques result in particles with a set of modifications, it is difficult to distinguish the effect of an individual feature on powder deposition behavior. This necessitates developing a predictive model capable of describing all influential factors on dry powder inhaler delivery. Therefore, in the current study, a model was constructed to correlate the inhaler device properties, inhalation flow rate, particle characteristics and drug/excipient physicochemical properties with the resultant fine particle fraction. The r² value of established correlation was 0.74 indicating 86% variability in FPF values is explained by the model with the mean absolute errors of 0.22 for the predicted values. The authors believe that this model is capable of predicting the lung deposition pattern of a formulation with an acceptable precision when the type of inhaler device, inhalation flow rate, physicochemical behavior of active and inactive ingredients and the particle characteristics of DPI formulations are considered.

On the relationship between blend state and dispersibility of adhesive mixtures containing active pharmaceutical ingredients

The objectives of this investigation were to study the evolution in blend state of adhesive mixtures containing the active pharmaceutical ingredients (APIs) salbutamol, budesonide and AZD5423 and to study the relationship between blend state and dispersibility of the mixtures, as assessed by the fine particle fraction (FPF). A series of adhesive mixtures of varied fines concentration were prepared for each API using the same type of carrier. Based on visual examination and powder mechanics, blend states were identified and summarized as blend state maps for each API. The dispersibility of the mixtures was studied using a Fast Screening Impactor (FSI) equipped with a ScreenHaler. The evolution in blend state differed between the APIs in terms of the width of the blend states. The structure of the adhesion layer also differed between the APIs, from relatively uniform to a heterogeneous layer with small agglomerates dispersed on the carrier surface. All three APIs expressed a similar type of bended relationship between FPF and fines concentration. However, the initial rate of increase and the fines concentration of the plateau differed between the APIs. The adhesive mixtures of all APIs followed the three main states in terms of structural evolution and the overall shape of the FPF-fines concentration profiles could be explained by the evolution in blend state. It is proposed that the structure of the adhesion layer is an important factor explaining the differences in blend state - blend dispersibility relationships between the APIs.

Controlling the performance of adhesive mixtures for inhalation using mixing energy

A concept of mixing energy, ME, has been developed and applied to blending of adhesive mixtures for inhalation in a high shear blender. Six different systems were investigated, four of which included a coating agent. For blends containing a coating agent, it is shown that the applied ME is key to the control of two important functional mechanisms: i) coating of the carrier by the coating agent, and ii) the dispersibility of the active pharmaceutical ingredient (API). The mass of the carrier was identified to be the mass which is relevant to the forces acting during mixing. The dispersibility in terms of the fine particle fraction (FPF) can be expressed as the product of two exponentials which both are functions of ME. The first factor accounts for the initial increase in FPF, while the second accounts for the decrease observed at extensive mixing. For adhesive mixtures without a coating agent, a similar decrease in FPF is observed when high forces are applied during mixing. Mechanistic interpretation of the behavior is provided.

Linking carrier morphology to the powder mechanics of adhesive mixtures for dry powder inhalers via a blend-state model

The aim of this study was to investigate how the carrier morphology affects the expression of blend states in adhesive mixtures as a function of surface coverage ratio (SCR) and to identify where transitions between the different states occur. Adhesive mixtures of five lactose carriers with varying contents of lactose fines, corresponding to blends with different SCR ranging from 0 to 6, were produced by low-shear mixing. The powder mechanics of the mixtures were characterized by bulk density, compressibility and permeability. The appearance of the carriers and blends was studied by scanning electron microscopy, light microscopy and atomic force microscopy. The size and morphology of the carriers had a crucial impact on the evolution of the blend state, and affected the powder mechanical properties of the mixtures. It was found that smaller carriers with little or no surface irregularities were more sensitive to additions of fines resulting in self-agglomeration of fines at relatively low SCR values. On the contrary, carriers with irregular surface structures and larger sizes were able to reach higher SCR values before self-agglomeration of fines occurred. This could be attributed to an increased deagglomeration efficiency of irregular and larger carriers and to fines predominantly adhering to open pores.

Relationships between surface coverage ratio and powder mechanics of binary adhesive mixtures for dry powder inhalers

The aim of this paper was to study relationships between the content of fine particles and the powder mechanics of binary adhesive mixtures and link these relationships to the blend state. Mixtures with increasing amounts of fine particles (increasing surface coverage ratios (SCR)) were prepared using Lactopress SD as carrier and micro particles of lactose as fines (2.7 µm). Indicators of unsettled bulk density, compressibility and flowability were derived and the blend state was visually examined by imaging. The powder properties studied showed relationships to the SCR characterised by stages. At low SCR, the fine particles predominantly gathered in cavities of the carriers, giving increased bulk density and unchanged or improved flow. Thereafter, increased SCR gave a deposition of particles at the enveloped carrier surface with a gradually more irregular adhesion layer leading to a reduced bulk density and a step-wise reduced flowability. The mechanics of the mixtures at a certain stage were dependent on the structure and the dynamics of the adhesion layer and transitions between the stages were controlled by the evolution of the adhesion layer. It is advisable to use techniques based on different types of flow in order to comprehensively study the mechanics of adhesive mixtures.