Dry powder aerosols generated by standardized entrainment tubes from drug blends with lactose monohydrate: 2. Ipratropium bromide monohydrate and fluticasone propionate

Scientific and regulatory activities initiated by the U.S. Food and drug administration to foster approvals of generic dry powder inhalers: Bioequivalence perspective

Regulatory science for generic dry powder inhalers (DPIs) in the United States (U.S.) has evolved over the last decade. In 2013, the U.S. Food and Drug Administration (FDA) published the draft product-specific guidance (PSG) for fluticasone propionate and salmeterol xinafoate inhalation powder. This was the first PSG for a DPI available in the U.S., which provided details on a weight-of-evidence approach for establishing bioequivalence (BE). A variety of research activities including in vivo and in vitro studies were used to support these recommendations, which have led to the first approval of a generic DPI in the U.S. for fluticasone propionate and salmeterol xinafoate inhalation powder in January of 2019. This review describes the scientific and regulatory activities that have been initiated by FDA to support the current BE recommendations for DPIs that led to the first generic DPI approvals, as well as research with novel in vitro and in silico methods that may potentially facilitate generic DPI development and approval.

Advanced Microparticulate/Nanoparticulate Respirable Dry Powders of a Selective RhoA/Rho Kinase (Rock) Inhibitor for Targeted Pulmonary Inhalation Aerosol Delivery

Pulmonary hypertension (PH) is a progressive disease that eventually leads to heart failure and potentially death for some patients. There are many unique advantages to treating pulmonary diseases directly and non-invasively by inhalation aerosols and dry powder inhalers (DPIs) possess additional unique advantages. There continues to be significant unmet medical needs in the effective treatment of PH that target the underlying mechanisms. To date, there is no FDA-approved DPI indicated for the treatment of PH. Fasudil is a novel RhoA/Rho kinase (ROCK) inhibitor that has shown great potential in effectively treating pulmonary hypertension. This systematic study is the first to report on the design and development of DPI formulations comprised of respirable nanoparticles/microparticles using particle engineering design by advanced spray drying. In addition, comprehensive physicochemical characterization, in vitro aerosol aerosol dispersion performance with different types of human DPI devices, in vitro cell-drug dose response cell viability of different human respiratory cells from distinct lung regions, and in vitro transepithelial electrical resistance (TEER) as air-interface culture (AIC) demonstrated that these innovative DPI fasudil formulations are safe on human lung cells and have high aerosol dispersion performance properties.

Design and Comprehensive Characterization of Tetramethylpyrazine (TMP) for Targeted Lung Delivery as Inhalation Aerosols in Pulmonary Hypertension (PH): In Vitro Human Lung Cell Culture and In Vivo Efficacy

This is the first study reporting on the design and development innovative inhaled formulations of the novel natural product antioxidant therapeutic, tetramethylpyrazine (TMP), also known as ligustrazine. TMP is obtained from Chinese herbs belonging to the class of Ligusticum. It is known to have antioxidant properties. It can act as a Nrf2/ARE activator and a Rho/ROCK inhibitor. The present study reports for the first time on the comprehensive characterization of raw TMP (non-spray dried) and spray dried TMP in a systematic manner using thermal analysis, electron microscopy, optical microscopy, and Raman spectroscopy. The in vitro aerosol dispersion performance of spray dried TMP was tested using three different FDA-approved unit-dose capsule-based human dry powder inhaler devices. In vitro human cellular studies were conducted on pulmonary cells from different regions of the human lung to examine the biocompatibility and non-cytotoxicity of TMP. Furthermore, the efficacy of inhaled TMP as both liquid and dry powder inhalation aerosols was tested in vivo using the monocrotaline (MCT)-induced PH rat model.

Fluticasone propionate-loaded solid lipid nanoparticles with augmented anti-inflammatory activity: optimisation, characterisation and pharmacodynamic evaluation on rats

This work aimed to elaborate an optimised fluticasone propionate (FP)-loaded solid lipid nanoparticles (SLNs) to enhance FP effectiveness for topical inflammatory remediation. The influences of drug amount, lipid, and surfactant ratios, on drug release pattern and stability were investigated utilising Box-Behnken design. Elaboration, characterisation, and pharmacodynamic evaluation in comparison with the marketed formulation (Cutivate® cream, 0.05%w/w FP), were conducted for the optimised SLNs. The optimised SLNs with a size of 248.3 ± 1.89 nm (PDI = 0.275) and -32.4 ± 2.85 mV zeta potential were evidenced good stability physiognomies. The optimised SLNs pre-treated rats exhibited non-significant difference in paw volume from that of the control group and showed a significant reduction in both PGE₂ and TNF-α levels by 51.5 and 61%, respectively, in comparison with the Carrageenan group. The optimised FP-loaded SLNs maximised the efficacy of FP towards inflammation alleviation that increase its potential as efficient implement in inflammatory skin diseases remediation.

Advanced design and development of nanoparticle/microparticle dual-drug combination lactose carrier-free dry powder inhalation aerosols

Rationale: lactose is the only FDA-approved carrier for dry powder inhaler (DPI) formulations in the US. Lactose carrier-based DPI products are contraindicated in patients with a known lactose allergy. Hence, inhaler formulations without lactose will benefit lactose allergic asthmatics. Objectives: to rationally design and develop lactose carrier-free dry powder inhaler formulations of fluticasone propionate and salmeterol xinafoate that will benefit people with known lactose allergy. The study also aims at improving the aerosol deposition of the dry powder formulation through advanced particle engineering design technologies to create inhalable powders consisting of nanoparticles/microparticles. Methods: advanced DPI nanoparticle/microparticle formulations were designed, developed and optimized using organic solution advanced closed-mode spray drying. The co-spray dried (co-SD) powders were comprehensively characterized in solid-state and in vitro comparative analysis of the aerodynamic performance of these molecularly mixed formulations was conducted with the marketed formulation of Advair® Diskus® interactive physical mixture. Measurements and main results: comprehensive solid-state physicochemical characterization of the powders showed that the engineered co-SD particles were small and spherical within the size range of 450 nm to 7.25 μm. Improved fine particle fraction and lower mass median aerodynamic diameter were achieved by these DPI nanoparticles/microparticles. Conclusions: this study has successfully produced a lactose-free dry powder formulation containing fluticasone propionate and salmeterol xinafoate with mannitol as excipient engineered as inhalable DPI nanoparticles/microparticles by advanced spray drying. Further, co-spray drying with mannitol and using Handihaler® device can generate higher fine particle mass of fluticasone/salmeterol. Mannitol, a mucolytic agent and aerosol performance enhancer, is a suitable excipient that can enhance aerosol dispersion of DPIs.

Inhaled salbutamol from aerolizer and diskus at different inhalation flows, inhalation volume and number of inhalations in both healthy subjects and COPD patients

The aim of the present study was to demonstrate the effect of inhalation-flow, inhalation-volume and number of inhalations on aerosol-delivery of inhaled-salbutamol from two different dry powder inhalers (DPIs) in both healthy-subjects and chronic obstructive pulmonary disease (COPD) patients. Relative pulmonary-bioavailability and systemic-bioavailability of inhaled-salbutamol, delivered by Diskus and Aerolizer, was determined in 24-COPD patients and 24-healthy subjects. The healthy-subjects and the COPD-patients participated in the study for 7 days in which they received 4 study doses of 200 μg salbutamol (one slow-inhalation, two slow-inhalations, one fast-inhalation, and two fast-inhalations) in four alternative days with 24 hr washout period after each dose. Two urine-samples were collected from each study subjects. The first was provided 30 min post inhalation (USAL0.5), as an index of relative pulmonary-bioavailability, and the second was pooled to 24 hr post inhalation (USAL24), as an index of systemic-bioavailability. Fast-inhalation resulted in significantly higher USAL0.5 and USAL24 than slow-inhalation (p˂0.05) after one-inhalation in both healthy-subjects and COPD-patients but there was no significant difference between slow and fast-inhalation after two-inhalations. One-inhalation resulted in significantly higher USAL0.5 and USAL24 in healthy-subjects compared to COPD-patient at both slow and fast-inhalation (p˂0.05) except USAL0.5 with Diskus at slow-inhalation there was no significant difference. Also, two-inhalations resulted in significantly higher USAL0.5 and USAL24 compared to one-inhalation at slow-inhalation only (p˂0.05). No significant difference was found between Aerolizer and Diskus except in USAL0.5 of one slow-inhalation in both health-subjects and COPD-patients (p = 0.048 and 0.047, respectively). Device-formula relation is present at low inhalation-flow since Diskus resulted in significantly higher USAL0.5 and USAL24 in healthy-subjects compared to COPD-patient at slow inhalation than Aerolizer. It is essential to inhale-twice and as hard and deep as possible from each dose when using DPI especially with COPD-patients having poor inspiratory efforts such as elderly patients and children.

Use of Computational Fluid Dynamics (CFD) Dispersion Parameters in the Development of a New DPI Actuated with Low Air Volumes

PURPOSE

To determine the predictive power of computational fluid dynamics (CFD)-based dispersion parameters in the development of a new inline DPI that is actuated with low volumes of air.

METHODS

Four new versions of a dose aerosolization and containment (DAC)-unit DPI were created with varying inlet and outlet orifice sizes and analyzed with results from five previous designs. A concurrent in vitro and CFD analysis was conducted to predict the emitted dose (ED; as a % of loaded dose) and aerosol mass median aerodynamic diameter (MMAD) produced by each device when actuated with 10 ml air bursts. CFD simulations of device operation were used to predict flow field and particle-based dispersion parameters.

RESULTS

Comparisons of experimental and CFD results indicated that multiple flow field and particle-based dispersion parameters could be used to predict ED (minimum RMS Error = 4.9%) and MMAD (minimum RMS Error = 0.04 μm) to a high degree of accuracy. Based on experiments, the best overall device produced mean (standard deviation; SD) ED = 82.9(4.3)% and mean MMAD (SD) = 1.73(0.07)μm, which were in close agreement with the CFD predictions.

CONCLUSIONS

A unique relationship was identified in the DAC-unit DPI in which reducing turbulence also reduced the MMAD.

Development of a New Inhaler for High-Efficiency Dispersion of Spray-Dried Powders Using Computational Fluid Dynamics (CFD) Modeling

Computational fluid dynamics (CFD) modeling offers a powerful tool for the development of drug delivery devices using a first principles approach but has been underutilized in the development of pharmaceutical inhalers. The objective of this study was to develop quantitative correlations for predicting the aerosolization behavior of a newly proposed dry powder inhaler (DPI). The dose aerosolization and containment (DAC) unit DPI utilizes inlet and outlet air orifices designed to maximize the dispersion of spray-dried powders, typically with low air volumes (~ 10 mL) and relatively low airflow rates (~ 3 L/min). Five DAC unit geometries with varying orifice outlet sizes, configurations, and protrusion distances were considered. Aerosolization experiments were performed using cascade impaction to determine mean device emitted dose (ED) and mass median aerodynamic diameter (MMAD). Concurrent CFD simulations were conducted to predict both flow field-based and particle-based dispersion parameters that captured different measures of turbulence. Strong quantitative correlations were established between multiple measures of turbulence and the experimentally observed aerosolization metrics of ED and MMAD. As expected, increasing turbulence produced increased ED with best case values reaching 85% of loaded dose. Surprisingly, decreasing turbulence produced an advantageous decrease in MMAD with values as low as approximately 1.6 μm, which is in contrast with previous studies. In conclusion, CFD provided valuable insights into the performance of the DAC unit DPI as a new device including a two-stage aerosolization process offering multiple avenues for future enhancements.

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.

Effect of Device Design and Formulation on the In Vitro Comparability for Multi-Unit Dose Dry Powder Inhalers

The focus of this investigation was to understand the design space to achieve comparable in vitro performance of two multi-unit dose dry powder inhalers (DPIs)—Flixotide® Accuhaler® (reference product) and MultiHaler® (test product). Flow field, pressure drop and particle trajectories within the test and reference DPI devices were modelled via computational fluid dynamics (CFD). Micronized fluticasone propionate (FP) was characterized to determine particle size distribution (PSD), specific surface area (SSA) and surface interfacial properties using cohesive-adhesive balance (CAB). CFD simulations suggested that the pressure drop and airflow velocity in the MultiHaler® were greater than Accuhaler®. Two modified test devices (MOD MH 1 and MOD MH 2) were manufactured with the introduction of by-pass channels in the airflow path, which achieved comparable specific resistance and airflow path between the test and reference devices. Assessment of reference product formulation in modified test devices suggested that MOD MH 2 achieved comparable in vitro performance to the reference product. CAB analysis suggested that adhesion of all FP batches to lactose was different, with batch D showing greatest and batch A least adhesion to lactose. Test DPI formulations were manufactured using four different batches of FP with milled or sieved lactose, and showed that batch A FP formulated with sieved lactose in MOD MH 2 device demonstrated the highest degree of similarity to the Accuhaler® in vitro deposition. Application of CFD modelling and material characterization of formulation raw materials enabled the modification of device and formulation critical material attributes to create an in vitro comparable device/formulation system to the reference product.

In vitro dry powder inhaler formulation performance considerations

It has long been desired to match airflow conditions during formulation evaluation to those of relevance to lung deposition. In this context several strategies have been adopted involving sampling at different: flow rate (without consideration of flow conditions, e.g. shear, Reynolds number, work function); pressure drop (with and without consideration of flow conditions) and; flow rate and pressure drop. Performance testing has focused on the influence of these sampling conditions on delivered dose uniformity and aerodynamic particle size distribution. However, in order to be physiologically relevant it is also important to know when the drug was delivered with respect to initiation of airflow as variation in this parameter would influence lung deposition. A light obscuration method of detecting the dose delivered from a dry powder inhaler while sampling for aerodynamic particle size distributions (APSD) by inertial impaction has been developed. Four formulations of albuterol sulfate and budesonide in sieved and milled lactose, respectively, were dispersed and their rate of delivery monitored. The differences observed have the potential to impact the site of delivery in the lungs. The rate of delivery of drug is clearly an important companion measurement to delivered dose and APSD if the intent is to predict the similarity of in vivo performance of dry powder inhaler products.

Aerodynamic and electrostatic properties of model dry powder aerosols: a comprehensive study of formulation factors

The impact of formulation variables on aerodynamic and electrostatic properties of dry powder aerosol particles is of great importance to the development of efficient and reproducible inhaler products. Systematic evaluation requires a well-designed series of experiments using appropriate methods. A factorial experimental design was employed. In broad terms, the conditions considered were two drugs, albuterol and budesonide, in combination with different excipients, drug concentrations, delivered doses, and metering system (capsule composition) and sampled under different flow conditions using standard entrainment tubes. Samples were collected in an electrical low-pressure impactor, to evaluate distribution of electrostatic properties, and an Andersen eight-stage nonviable cascade impactor, to estimate aerodynamic particle size distribution, concurrently. The deposition studies allowed calculation of approximate per particle charge levels for drug. The results showed very high particle charge levels, often in the 1,000-10,000 of elementary charges per particle range, orders of magnitude higher than charge levels predicted by the Boltzmann charge distribution. The charge levels are considerably higher than had previously been estimated (200e per particle).

Physicochemical characterization and aerosol dispersion performance of organic solution advanced spray-dried cyclosporine A multifunctional particles for dry powder inhalation aerosol delivery

In this systematic and comprehensive study, inhalation powders of the polypeptide immunosuppressant drug – cyclosporine A – for lung delivery as dry powder inhalers (DPIs) were successfully designed, developed, and optimized. Several spray drying pump rates were rationally chosen. Comprehensive physicochemical characterization and imaging was carried out using scanning electron microscopy, hot-stage microscopy, differential scanning calorimetry, powder X-ray diffraction, Karl Fischer titration, laser size diffraction, and gravimetric vapor sorption. Aerosol dispersion performance was conducted using a next generation impactor with a Food and Drug Administration-approved DPI device. These DPIs displayed excellent aerosol dispersion performance with high values in emitted dose, respirable fraction, and fine particle fraction. In addition, novel multifunctional inhalation aerosol powder formulations of cyclosporine A with lung surfactant-mimic phospholipids were also successfully designed and developed by advanced organic solution cospray drying in closed mode. The lung surfactantmimic phospholipids were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-snglycero- 3-(phosphor-rac-1-glycerol). These cyclosporine A lung surfactant-mimic aerosol powder formulations were comprehensively characterized. Powder X-ray diffraction and differential scanning calorimetry confirmed that the phospholipid bilayer structure in the solid state was preserved following advanced organic solution spray drying in closed mode. These novel multifunctional inhalation powders were optimized for DPI delivery with excellent aerosol dispersion performance and high aerosol performance parameters.

Aerodynamic factors responsible for the deaggregation of carrier-free drug powders to form micrometer and submicrometer aerosols

PURPOSE

To employ in vitro experiments combined with computational fluid dynamics (CFD) analysis to determine which aerodynamic factors were most responsible for deaggregating carrier-free powders to form micrometer and submicrometer aerosols from a capsule-based platform.

METHODS

Eight airflow passages were evaluated for deaggregation of the aerosol including a standard constricted tube, impaction surface, 2D mesh, inward radial jets, and newly proposed 3D grids and rod arrays. CFD simulations were implemented to evaluate existing and new aerodynamic factors for deaggregation and in vitro experiments were used to evaluate performance of each inhaler.

RESULTS

For the carrier-free formulation considered, turbulence was determined to be the primary deaggregation mechanism. A strong quantitative correlation was established between the mass median diameter (MMD) and newly proposed non-dimensional specific dissipation (NDSD) factor, which accounts for turbulent energy, inverse of the turbulent length scale, and exposure time. A 3D rod array design with unidirectional elements maximized NDSD and produced the best deaggregation with MMD<1 μm.

CONCLUSIONS

The new NDSD parameter can be used to develop highly effective dry powder inhalers like the 3D rod array that can efficiently produce submicrometer aerosols for next-generation respiratory drug delivery applications.

Design and physicochemical characterization of advanced spray-dried tacrolimus multifunctional particles for inhalation

The aim of this study was to design, develop, and optimize respirable tacrolimus microparticles and nanoparticles and multifunctional tacrolimus lung surfactant mimic particles for targeted dry powder inhalation delivery as a pulmonary nanomedicine. Particles were rationally designed and produced at different pump rates by advanced spray-drying particle engineering design from organic solution in closed mode. In addition, multifunctional tacrolimus lung surfactant mimic dry powder particles were prepared by co-dissolving tacrolimus and lung surfactant mimic phospholipids in methanol, followed by advanced co-spray-drying particle engineering design technology in closed mode. The lung surfactant mimic phospholipids were 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and 1,2-dipalmitoyl-sn-glycero-3-[phosphor-rac-1-glycerol]. Laser diffraction particle sizing indicated that the particle size distributions were suitable for pulmonary delivery, whereas scanning electron microscopy imaging indicated that these particles had both optimal particle morphology and surface morphology. Increasing the pump rate percent of tacrolimus solution resulted in a larger particle size. X-ray powder diffraction patterns and differential scanning calorimetry thermograms indicated that spray drying produced particles with higher amounts of amorphous phase. X-ray powder diffraction and differential scanning calorimetry also confirmed the preservation of the phospholipid bilayer structure in the solid state for all engineered respirable particles. Furthermore, it was observed in hot-stage micrographs that raw tacrolimus displayed a liquid crystal transition following the main phase transition, which is consistent with its interfacial properties. Water vapor uptake and lyotropic phase transitions in the solid state at varying levels of relative humidity were determined by gravimetric vapor sorption technique. Water content in the various powders was very low and well within the levels necessary for dry powder inhalation, as quantified by Karl Fisher coulometric titration. Conclusively, advanced spray-drying particle engineering design from organic solution in closed mode was successfully used to design and optimize solid-state particles in the respirable size range necessary for targeted pulmonary delivery, particularly for the deep lung. These particles were dry, stable, and had optimal properties for dry powder inhalation as a novel pulmonary nanomedicine.

Influence of peak inspiratory flow rates and pressure drops on inhalation performance of dry powder inhalers

The aim of this study was to reveal the relationship between human inspiratory flow patterns and the concomitant drops in pressure in different inhalation devices, and the influence of the devices on inhalation performance. As a model formulation for inhalers, a physically mixed dry powder composed of salbutamol sulfate and coarse lactose monohydrate was selected. The drops in pressure at 28.3 L/min of three inhalation devices, Single-type, Dual-type, and Reverse-type, was 1.0, 5.1, and 8.7 kPa, respectively. Measurements of human inspiratory patterns revealed that although the least resistant device (Single) had large inter- and intra-individual variation of peak flow rate (PFR), the coefficients of variation of PFR of the three devices were almost the same. In tests with a human inspiratory flow simulator in vitro, inhalation performance was higher, but the variation in inhalation performance in the range of human flow patterns was wider, for the more resistant device. To minimize the intra- and inter-individual variation in inhalation performance for the model formulation in this study, a formulation design that allows active pharmaceutical ingredient to detach from the carrier with a lower inhalation flow rate is needed.

Effect of device design on the in vitro performance and comparability for capsule-based dry powder inhalers

This study investigated the effect of modifying the design of the Cyclohaler on its aerosolization performance and comparability to the HandiHaler at multiple flow rates. The Cyclohaler and HandiHaler were designated as model test and reference unit-dose, capsule-based dry powder inhalers (DPIs), respectively. The flow field, pressure drop, and carrier particle trajectories within the Cyclohaler and HandiHaler were modeled via computational fluid dynamics (CFD). With the goal of achieving in vitro comparability to the HandiHaler, the CFD results were used to identify key device attributes and to design two modifications of the Cyclohaler (Mod 1 and Mod 2), which matched the specific resistance of the HandiHaler but exhibited different cyclonic flow conditions in the device. Aerosolization performance of the four DPI devices was evaluated by using the reference product's capsule and formulation (Spiriva capsule) and a multistage cascade impactor. The in vitro data showed that Mod 2 provided a closer match to the HandiHaler than the Cyclohaler and Mod 1 at 20, 39, and 55 l/min. The in vitro and CFD results together suggest that matching the resistance of test and reference DPI devices is not sufficient to attain comparable aerosolization performance, and the improved in vitro comparability of Mod 2 to the HandiHaler may be related to the greater degree of similarities of the flow rate of air through the pierced capsule (Q(c)) and the maximum impact velocity of representative carrier particles (V(n)) in the Cyclohaler-based device. This investigation illustrates the importance of enhanced product understanding, in this case through the CFD modeling and in vitro characterization of aerosolization performance, to enable identification and modification of key design features of a test DPI device for achieving comparable aerosolization performance to the reference DPI device.

Influence of crystal form of ipratropium bromide on micronisation and aerosolisation behaviour in dry powder inhaler formulations

Objectives

This study aimed to investigate the relationship between the mechanical properties of anhydrous and monohydrate ipratropium bromide (IB) crystals, their processing behaviour upon air-jet micronisation and aerosolisation performance in dry powder inhaler (DPI) formulations.

Methods

IB monohydrate and anhydrous crystals were produced from seed crystals and supercritical carbon dioxide crystallisation, respectively. Young's modulus of anhydrous and monohydrate IB crystals was determined using nanoindentation. For air-jet micronised crystals, the physicochemical and surface interfacial properties via the cohesive–adhesive balance (CAB) approach were investigated. These data were correlated to in-vitro aerosolisation performance of carrier-based DPI formulations containing either anhydrous or monohydrate IB.

Key findings

Particle size and Young's modulus of both crystals were similar and this was reflected in their similar processing upon micronisation. Particle size of micronised anhydrous and monohydrate crystals were similar. CAB measurements of the micronised particles of monohydrate or anhydrous forms of IB with respect to lactose were 0.70 (R2 = 0.998) and 0.77 (R2 = 0.999), respectively. These data suggested that both samples had similar adhesion to lactose, which correlated with their similar in-vitro aerosolisation performance in DPI formulations.

Conclusions

Monohydrate and anhydrous crystals of IB exhibited similar mechanical properties and interfacial properties upon secondary processing. As a result, the performance of the DPI formulations were similar.

Advanced microscopy techniques to assess solid-state properties of inhalation medicines

Efficient control and characterisation of the physico-chemical properties of active pharmaceutical ingredients (APIs) and excipients for orally inhaled drug products (OIDPs) are critical to successful product development. Control and reduction of risk require the introduction of a material science based approach to product development and the use of advanced analytical tools in understanding how the solid-state properties of the input materials influence structure and product functionality. The key issues to be addressed, at a microscopic scale, are understanding how the critical quality attributes of input materials influence surface, interfacial and particulate interactions within OIDPs. This review offers an in-depth discussion on the use of advanced microscopy techniques in characterising of the solid-state properties of particulate materials for OIDPs. The review covers the fundamental principles of the techniques, instrumentation types, data interpretation and specific applications in relation to the product development of OIDPs.