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.

The match between adhesive mixture powder formulations for inhalation and the inhaler device.

The device or the formulation? Which one governs drug dispersibility from the inhaler? To address this question, three budesonide-containing reservoir DPIs: Novopulmon Novolizer®, Giona Easyhaler® and DuoResp Spiromax®, were analyzed using the Next Generation Impactor, NGI. Thereafter, the devices were carefully opened, emptied, and formulations were switched between devices. Finally, three 'prototype' formulations with carriers of different particle size were produced and tested in the Novolizer and Easyhaler devices. Among the DPI products, the two devices which have a flow path with a cyclone-type geometry, i.e., the Novolizer and the Spiromax, yielded a fine particle fraction, FPF, above 40%. The Easyhaler, which has a straight mouthpiece outlet, produced an FPF of 18%. When the Novopulmon and the DuoResp formulations were assayed in the Easyhaler device, poor fine particle fractions were obtained. To the contrary, the Giona formulation produced a high FPF when tested in the Novolizer device. The results clearly show that the device is the dominating factor to dispersibility for the investigated products. Along the same lines, all three 'prototype' formulations produced high fine particle fractions in the Novolizer device, with the formulation with the largest carrier giving the best performance. Tested in the Easyhaler device, the prototype formulations produced low fine particle fractions, but interestingly, the formulation with the smallest carrier particle size yielded the highest FPF. It can be concluded that there is a link between inhaler design and the effect of carrier particle size, where larger carriers provide better dispersion in cyclone-type devices while smaller carriers seem to be more beneficial for inhalers which has a straight flow path for the powder formulation.

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.

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.

The unhappy chaperone.

Chaperones protect other proteins against misfolding and aggregation, a key requirement for maintaining biological function. Experimental observations of changes in solubility of amyloid proteins in the presence of certain chaperones are discussed here in terms of thermodynamic driving forces. We outline how chaperones can enhance amyloid solubility through the formation of heteromolecular aggregates (co-aggregates) based on the second law of thermodynamics and the flux towards equal chemical potential of each compound in all phases of the system. Higher effective solubility of an amyloid peptide in the presence of chaperone implies that the chemical potential of the peptide is higher in the aggregates formed under these conditions compared to peptide-only aggregates. This must be compensated by a larger reduction in chemical potential of the chaperone in the presence of peptide compared to chaperone alone. The driving force thus relies on the chaperone being very unhappy on its own (high chemical potential), thus gaining more free energy than the amyloid peptide loses upon forming the co-aggregate. The formation of heteromolecular aggregates also involves the kinetic suppression of the formation of homomolecular aggregates. The unhappiness of the chaperone can explain the ability of chaperones to favour an increased population of monomeric client protein even in the absence of external energy input, and with broad client specificity. This perspective opens for a new direction of chaperone research and outlines a set of outstanding questions that aim to provide additional cues for therapeutic development in this area.

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.

Quantification of surface composition and surface structure of inhalation powders using TOF-SIMS.

A multivariate TOF-SIMS methodology has been developed and applied to quantify surface composition and chemical distribution for dry powder blends. Surface properties are often critical to the behavior of powder formulations, especially in the case of dry powders for inhalation, as surface properties directly affect inter-particulate forces and, hence, the dispersibility of the formulation. The mass spectrum at each pixel was fit to a linear combination of reference spectra obtained by non-negatively constrained alternating least squares. From the pixel compositions, average surface coverage and a range of other image features were calculated. Two kinds of systems have been examined: 1) binary blends of lactose particles and coating agents, and 2) blends of different inhalation drugs with carrier lactose. For both kinds of systems, detailed insight into the surface composition and structure could be derived. For the former study, TOF-SIMS results were compared with a complementary surface analysis technique, XPS.

Correlations between surface composition and aerosolization of jet-milled dry powder inhaler formulations with pharmaceutical lubricants.

Co-jet-milling drugs and lubricants may enable simultaneous particle size reduction and surface coating to achieve satisfactory aerosolization performance. This study aims to establish the relationship between surface lubricant coverage and aerosolization behavior of a model drug (ciprofloxacin HCl) co-jet-milled with lubricants [magnesium stearate (MgSt) or l-leucine]. The co-jet-milled formulations were characterized for particle size, morphology, cohesion, Carr's index, and aerosolization performance. The surface lubricant coating was assessed by probing surface chemical composition using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectrometry (ToF-SIMS). The effects of co-jet-milling on the surface energy and in vitro dissolution of ciprofloxacin were also evaluated. Our results indicated that, in general, the ciprofloxacin co-jet-milled with l-leucine at >0.5% w/w showed a significant higher fine particle fraction (FPF) compared with the ciprofloxacin jet-milled alone. The FPF values plateau at or above 5% w/w for both MgSt and l-leucine. We have established the quantitative correlations between surface lubricant coverage and aerosolization in the tested range for each of the lubricants. More importantly, our results suggest different mechanisms to improve aerosolization for MgSt-coating and l-leucine-coating, respectively: MgSt-coating reduces inter-particulate interactions through the formation of low surface energy coating films, while l-leucine-coating not only reduces the surface energy but also creates rough particle surfaces that reduce inter-particulate contact area. Furthermore, surface coatings with 5% w/w MgSt (which is hydrophobic) did not lead to substantial changes in in vitro dissolution. Our findings have shown that the coating structure/quality and their effects could be highly dependent on the process and the coating material. The findings from this mechanistic study provide fundamental understanding of the critical effects of MgSt and l-leucine surface coverages on aerosolization and powder flow properties of inhalation particles.

Characterization of acoustic emission analysis in applications for inhalation device performance assessment.

Acoustic Emission (AE) measurement technology has gained wide appreciation in material sciences and process monitoring. In inhalation research, AE has been used for adherence indicating applications in clinical studies. Promising results from feasibility studies using AE combined with multivariate data analysis (AE-MVDA) in the analysis of devices for inhalation have prompted a broader study reported in this paper. This work presents the novel application of AE-MVDA for assessment of the combined inhalation device and formulation performance. The purpose is to evaluate the benefits that this technology can provide to inhalation product development programs. The work was carried out using two different dry powder inhaler device model systems while investigating different performance features. The devices were filled with dry powder formulations with both placebo and with active pharmaceutical ingredient (API). The acquired AE data was analyzed using multivariate data analysis tools such as Principal component analysis (PCA) and orthogonal projections to latent structures (OPLS). The AE profiles were indicative for device and formulation performance. Normal and deviating performances were readily picked up in the AE data. Moreover, performance trends between doses withdrawn from the inhalers were also observable. Lastly, differences in the AE profile between the formulations could be detected. The overall conclusion from the AE-MVDA measurement approach evaluation is that it has the potential to add value as a cost-effective, non-invasive quality and performance monitoring technology both in development and in production of inhaled medicines.

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.

Towards quantitative prediction of the performance of dry powder inhalers by multi-scale simulations and experiments.

This work demonstrates the use of multi-scale simulations coupled with experiments to build a quantitative prediction tool for the performance of adhesive mixtures in a dry powder inhaler (DPI). Using discrete element model (DEM), the behaviour of fine-carrier particle assemblies upon different mechanisms encountered during dose entrainment and dispersion can be described at the individual particle level. Combining these results with computational fluid dynamics (CFD) simulations, the complete dosing event from a DPI can be captured and key performance measures can be extracted. A concept of apparent surface energy, ASE, was introduced to overcome challenges associated with the complex particle properties, e.g. irregular particle shapes and surface roughness. This approach correctly predicts trends observed experimentally regarding API adhesivity, flow rate and device geometry. By incorporating the effects of drug load, critical adhesion and surface energy distributions to the simulation tool, the fine particle fraction could be predicted with good agreement to experiments for two different formulations in two different devices at two flow rates. It is concluded that multi-scale simulations provide a useful tool to support device and formulation development, as well as to gain further insight into the physical mechanisms governing dispersion from DPIs.

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.

Mechanistic investigation of mixing and segregation of ordered mixtures: experiments and numerical simulations.

Pulmonary delivery of cohesive and micronized drugs through dry powder inhalers (DPIs) is traditionally achieved through the formation of ordered mixtures. In order to improve the mechanistic understanding of formation of ordered mixtures, the system consisting of micronized lactose (AZFL, representative of an active pharmaceutical ingredient) and a coarse particle carrier (LH100) is investigated as a function of different process and material variables in a high shear mixer (HSM) and in a low shear double cone (DCN) blender, using both experimental and numerical methods. Process insight is developed using a Discrete Element Method (DEM) based numerical model which could predict the formation of ordered mixtures in the two blenders and was verified against experimental determinations. Spatial and temporal evolution of granular flow are visualized and quantified in silico to reveal distinguishing features of both blenders to aid in rational selection of blenders and process parameters.

Development of a Rational Design Space for Optimizing Mixing Conditions for Formation of Adhesive Mixtures for Dry-Powder Inhaler Formulations.

The purpose of the present study was to develop guidance toward rational choice of blenders and processing conditions to make robust and high performing adhesive mixtures for dry-powder inhalers and to develop quantitative experimental approaches for optimizing the process. Mixing behavior of carrier (LH100) and AstraZeneca fine lactose in high-shear and low-shear double cone blenders was systematically investigated. Process variables impacting the mixing performance were evaluated for both blenders. The performance of the blenders with respect to the mixing time, press-on forces, static charging, and abrasion of carrier fines was monitored, and for some of the parameters, distinct differences could be detected. A comparison table is presented, which can be used as a guidance to enable rational choice of blender and process parameters based on the user requirements. Segregation of adhesive mixtures during hopper discharge was also investigated.

Dispersibility of lactose fines as compared to API in dry powders for inhalation.

This work investigates the dispersion performance of fine lactose particles as function of processing time, and compares it to the API, using Beclomethasone Dipropionate (BDP) as model API. The total load of fine particles is kept constant in the formulations while the proportions of API and lactose fines are varied. Fine particle assessment demonstrates that the lactose fines have higher dispersibility than the API. For standard formulations, processing time has a limited effect on the Fine Particle Fraction (FPF). For formulations containing magnesium stearate (MgSt), FPF of BDP is heavily influenced by processing time, with an initial increase, followed by a decrease at longer mixing times. An equation modeling the observed behavior is presented. Surprisingly, the dispersibility of the lactose fines present in the same formulation remains unaffected by mixing time. Magnesium analysis demonstrates that MgSt is transferred to the fine particles during the mixing process, thus lubrication both BDP and lactose fines, which leads to an increased FPF. Dry particle sizing of the formulations reveals a loss of fine particles at longer mixing times. Incorporation of fine particles into the carrier surfaces is believed to be behind this, and is hence a mechanism of importance as regards the dispersion performance of dry powders for inhalation.

Mechanistic time scales in adhesive mixing investigated by dry particle sizing.

This study exploits the mechanisms governing blending of adhesive mixtures, i.e. random mixing, de-agglomeration and adhesion, and their relative importance to achieve mixing homogeneity. To this end, blending of micronized particles (fines) with carrier particles was carried out using a high shear mixer. Dry particle sizing using laser diffraction coupled with a strong powder dispersion unit was employed to measure the fines content in samples collected during mixing, and hence to assess blend homogeneity. The method was also employed to evaluate the relative strength of the agglomerates present in the fines. Particle sizing using a non-destructive imaging technique was used to monitor changes in particle size during blending. It could be shown that the de-agglomeration of the fine-particle agglomerates is the slowest mechanism and hence the rate-limiting step as regards achieving a homogeneous adhesive mixture. Consequently, a longer mixing time is needed for blending of larger agglomerates. Being fast, simple and reproducible, the laser diffraction technique was shown to be an efficient method for measurement of fine particle content and homogeneity of a mixture, while the non-destructive image analysis was able to give relevant information on the rate of de-agglomeration of the fine-particle agglomerates as well as on the size of the resulting carrier-fine particle assemblies.

Modeling dispersion of dry powders for inhalation. The concepts of total fines, cohesive energy and interaction parameters.

A range of carrier based dry powder formulations consisting of micronized drug, carrier lactose and, in some formulations, lactose fines were produced and tested for dispersibility, i.e. fine particle fraction (FPF). Two different drugs were used, budesonide (BUD) and beclomethasone dipropionate (BDP). A model based on the total amount of fines (TF) and the cohesive energy (CE) of the formulation is proposed, where TF is the sum of added drug, lactose fines and the fines inherent to the carrier. The expression for CE is derived from regular solutions theory and allows calculation of interparticle interaction parameters. The model was able to describe experimental data well, such as the decrease in FPF when the proportion of drug is increased at a constant TF level and the non-linear effects seen when a cohesive drug is added to carrier. BDP and BUD were found to be 5.3 times and 1.8 times more cohesive than lactose fines respectively. The model hence provides a link between the macroscopic behavior of a dry powder formulation and the interaction between the different species at the particulate level.

The apparent plasticizing effect of polyethylene glycol (PEG) on the crystallinity of spray dried lactose/PEG composites.

Aqueous solutions of lactose and polyethylene glycol (PEG) were spray dried in a Büchi Model 191 spray dryer with the aim to investigate the effect of PEG on the crystallinity of the composite. A PEG concentration of 10.7% by weight of solids was studied for PEG 200, 600, 1500, 4000 and 8000. For PEG 200 and 4000 additional concentrations from 1.5-19.3% to 1.5-32.4%, respectively, were investigated. The spray dried composites were analysed with X-ray powder diffraction and modulating differential scanning calorimetry. The crystallinity of lactose in the composites varied from 0% to 60%, dependent on the molecular weight and concentration of PEG. Apparently, lactose crystallinity is promoted by low molecular weight and high concentration of the PEG. PEG did not affect the lactose glass transition temperature. It is suggested that lactose and PEG are solidified separately during spray drying and that partial crystallization of lactose is associated with effects of PEG on the rate of drying.

Particle formation and capture during spray drying of inhalable particles.

An investigation of the spray drying process is made in great detail regarding particle formation and capture efficiency with focus on the production of inhalable particles. Mannitol was spray dried as model substance and the spray-dried products were characterized. The resulting products consisted of smooth spheres with a volume median diameter of 2.2-5.5 microm, and narrow size distributions. The investigation was performed in pilot scale of sufficient size to draw general conclusions and make some recommendations. It has been shown that the size of particles is decreased when the feed concentration is decreased, the nozzle gas/feed flow mass ratio increased, and the droplet size decreased. The collection efficiency of the cyclone device used in this study was shown to have a cut-off of 2 microm, i.e., 50% of the particles less than 2 microm are not captured. The data reported indicate that the majority of the single particles formed here, <5 microm, arise from single droplets (of about 10 microm) and are solid, nonporous particles.