Colistin Powders with High Aerosolisation Efficiency for Respiratory Infection: Preparation and In Vitro Evaluation

Liposomal Formulation Reduces Transport and Cell Uptake of Colistin in Human Lung Epithelial Calu-3 Cell and 3D Human Lung Primary Tissue Models

Respiratory tract infections caused by multi-drug-resistant (MDR) bacteria have been a severe risk to human health. Colistin is often used to treat the MDR Gram-negative bacterial infections as a last-line therapy. Inhaled colistin can achieve a high concentration in the lung but none of aerosolized colistin products has been approved in the USA. Liposome has been reported as an advantageous formulation strategy for antibiotics due to its controlled release profile and biocompatibility. We have developed colistin liposomal formulations in our previous study. In the present study, the cellular uptake and transport of colistin in colistin liposomes were examined in two human lung epithelium in vitro models, Calu-3 monolayer and EpiAirway 3D tissue models. In both models, cellular uptake (p < 0.05) and cellular transport (p < 0.01) of colistin were significantly reduced by the colistin liposome compared to the colistin solution. Our findings indicate that inhaled colistin liposomes could be a promising treatment for extracellular bacterial lung infections caused by MDR Pseudomonas aeruginosa (P. aeruginosa).

The quest to deliver high-dose rifampicin: can the inhaled approach help?

INTRODUCTION

Tuberculosis (TB) is a global health problem that poses a challenge to global treatment programs. Rifampicin is a potent and highly effective drug for TB treatment; however, higher oral doses than the standard dose (10 mg/kg/day) rifampicin may offer better efficacy in TB treatment.

AREAS COVERED

High oral dose rifampicin is not implemented in anti-TB regimens yet and requires about a 3-fold increase in dose for increased efficacy. We discuss inhaled delivery of rifampicin as an alternative or adjunct to oral high-dose rifampicin. Clinical results of safety, tolerability, and patient compliance with antibiotic dry powder inhalers are reviewed.

EXPERT OPINION

Clinical trials suggest that an approximately 3-fold increase in the standard oral dose of rifampicin may be required for better clinical outcomes. On the other hand, animal studies suggest that inhaled rifampicin can deliver a high concentration of the drug to the lungs and achieve approximately double the plasma concentration than that from oral rifampicin. Clinical trials on inhaled antibiotics suggest that dry powder inhalation is a patient-friendly and well-tolerated approach in treating respiratory infections compared to conventional treatments. Rifampicin, a well-known anti-TB drug given orally, is a good candidate for clinical development as a dry powder inhaler.

Improved Aerosolization Stability of Inhalable Tobramycin Powder Formulation by Co-Spray Drying with Colistin

PURPOSE

Tobramycin shows synergistic antibacterial activity with colistin and can reduce the toxic effects of colistin. The purpose of this study is to prepare pulmonary powder formulations containing both colistin and tobramycin and to assess their in vitro aerosol performance and storage stability.

METHODS

The dry powder formulations were manufactured using a lab-scale spray dryer. In vitro aerosol performance was measured using a Next Generation Impactor. The storage stability of the dry powder formulations was measured at 22°C and two relative humidity levels - 20 and 55%. Colistin composition on the particle surface was measured using X-ray photoelectron spectroscopy.

RESULTS

Two combination formulations, with 1:1 and 1:5 molar ratios of colistin and tobramycin, showed fine particle fractions (FPF) of 85%, which was significantly higher than that of the spray dried tobramycin (45%). FPF of the tobramycin formulation increased significantly when stored for four weeks at both 20% and 55% RH. In contrast, FPF values of both combination formulations and spray dried colistin remained stable at both humidity levels. Particle surface of each combination was significantly enriched in colistin molecules; 1:5 combination showed 77% by wt. colistin.

CONCLUSIONS

The superior aerosol performance and aerosolization stability of 1:1 and 1:5 combination formulations of colistin and tobramycin could be attributed to enrichment of colistin on the co-spray dried particle surface. The observed powder properties may be the result of a surfactant-like assembly of these colistin molecules during spray drying, thus forming a hydrophobic particle surface.

Spray-freeze-dried inhalable composite microparticles containing nanoparticles of combinational drugs for potential treatment of lung infections caused by Pseudomonas aeruginosa

The multi-drug resistance of Pseudomonas aeruginosa is an overwhelming cause of terminal and persistent lung infections in cystic fibrosis (CF) patients. Antimicrobial synergy has been shown for colistin and ivacaftor, and our study designed a relatively high drug-loading dry powder inhaler formulation containing nanoparticles of ivacaftor and colistin. The ivacaftor-colistin nanosuspensions (Iva-Col-NPs) were prepared by the anti-solvent method with different stabilizers. Based on the aggregation data, the formulation 7 (F7) with DSPG-PEG-OMe as the stabilizer was selected for further studies. The F7 consisted of ivacaftor, colistin and DSPG-PEG-OMe with a mass ratio of 1:1:1. The F7 powder formulation was developed using the ultrasonic spray-freeze-drying method and exhibited a rough surface with relatively high fine particle fraction values of 61.4 ± 3.4% for ivacaftor and 63.3 ± 3.3% for colistin, as well as superior emitted dose of 97.8 ± 0.3% for ivacaftor and 97.6 ± 0.5% for colistin. The F7 showed very significant dissolution improvement for poorly water soluble ivacaftor than the physical mixture. Incorporating two drugs in a single microparticle with synchronized dissolution and superior aerosol performance will maximize the synergy and bioactivity of those two drugs. Minimal cytotoxicity in Calu-3 human lung epithelial cells and enhanced antimicrobial activity against colistin-resistant P. aeruginosa suggested that our formulation has potential to improve the treatment of CF patients with lung infections.

Status of inhalable antimicrobial agents for lung infection: progress and prospects

Introduction: Available parenteral and oral administration of antimicrobial agents (AMAs) in respiratory infections often show less penetration into the lung parenchyma. Due to inappropriate dose availability, the rate of antibiotic resistance is increasing gradually. Inhaled antibiotics intensely improve the availability of drugs at the site of respiratory infections. This targeted delivery minimizes systemic exposure and associated toxicity.Area covers: This review was performed by searching in the scientific database like PubMed and several trusted government sites like fda.gov, cdc.gov, ClinicalTrials.gov, etc. For better understanding, AMAs are classified in different stages of approval. Mechanism and characterization of pulmonary drug deposition section helps to understand the effective delivery of AMAs to the respiratory tract. There is a need for proper adoption of delivery devices for inhalable AMAs. Thus, delivery devices are extensively explained. Inspiratory flow has a remarkable impact on the delivery device that has been explained in detail.Expert opinion: Pulmonary delivery restricts the bulk administration of drugs in comparison with other routes. Therefore, novel AMAs with higher bactericidal activity at lower concentrations need to be synthesized. Extensive research is indeed in developing innovative delivery devices that would able to deliver higher doses of AMAs through the pulmonary route.

Novel formulations and drug delivery systems to administer biological solids

Recent advances in formulation sciences have expanded the previously limited design space for biological modalities, including peptide, protein, and vaccine products. At the same time, the discovery and application of new modalities, such as cellular therapies and gene therapies, have presented formidable challenges to formulation scientists. We explore these challenges and highlight the opportunities to overcome them through the development of novel formulations and drug delivery systems as biological solids. We review the current progress in both industry and academic laboratories, and we provide expert perspectives in those settings. Formulation scientists have made a tremendous effort to accommodate the needs of these novel delivery routes. These include stability-preserving formulations and dehydration processes as well as dosing regimes and dosage forms that improve patient compliance.

Inhaled fixed-dose combination powders for the treatment of respiratory infections

INTRODUCTION

Respiratory infections are a major cause of morbidity and mortality. As an alternative to systemic drug administration, inhaled drug delivery can produce high drug concentrations in the lung tissue to overcome resistant bacteria. The development of inhaled fixed-dose combination powders (I-FDCs) is promising next step in this field, as it would enable simultaneous drug-drug or drug-adjuvant delivery at the site of infection, thereby promoting synergistic activity and improving patient compliance.

AREAS COVERED

This review covers the clinical and pharmaceutical rationales for the development of I-FDCs for the treatment of respiratory infections, relevant technologies for particle and powder generation, and obstacles which must be addressed to achieve regulatory approval.

EXPERT OPINION

I-FDCs have been widely successful in the treatment of asthma and chronic obstructive pulmonary disease; however, application of I-FDCs towards the treatment of respiratory infections carries additional challenges related to the high dose requirements and physicochemical characteristics of anti-infective drugs. At present, co-spray drying is an especially promising approach for the development of composite fixed-dose anti-infective particles for inhalation. Though the majority of fixed-dose research has thus far focused on the combination of multiple antibiotics, future work may shift to the additional inclusion of immunomodulatory agents or repurposed non-antibiotics.

Dry Powder for Pulmonary Delivery: A Comprehensive Review

The pulmonary route has long been used for drug administration for both local and systemic treatment. It possesses several advantages, which can be categorized into physiological, i.e., large surface area, thin epithelial membrane, highly vascularized, limited enzymatic activity, and patient convenience, i.e., non-invasive, self-administration over oral and systemic routes of drug administration. However, the formulation of dry powder for pulmonary delivery is often challenging due to restrictions on aerodynamic size and the lung’s lower tolerance capacity in comparison with an oral route of drug administration. Various physicochemical properties of dry powder play a major role in the aerosolization, deposition, and clearance along the respiratory tract. To prepare suitable particles with optimal physicochemical properties for inhalation, various manufacturing methods have been established. The most frequently used industrial methods are milling and spray-drying, while several other alternative methods such as spray-freeze-drying, supercritical fluid, non-wetting templates, inkjet-printing, thin-film freezing, and hot-melt extrusion methods are also utilized. The aim of this review is to provide an overview of the respiratory tract structure, particle deposition patterns, and possible drug-clearance mechanisms from the lungs. This review also includes the physicochemical properties of dry powder, various techniques used for the preparation of dry powders, and factors affecting the clinical efficacy, as well as various challenges that need to be addressed in the future.

Novel Approaches for the Treatment of Pulmonary Tuberculosis

Tuberculosis (TB) is a contagious airborne disease caused by Mycobacterium tuberculosis, which primarily affects human lungs. The progression of drug-susceptible TB to drug-resistant strains, MDR-TB and XDR-TB, has become worldwide challenge in eliminating TB. The limitations of conventional TB treatment including frequent dosing and prolonged treatment, which results in patient’s noncompliance to the treatment because of treatment-related adverse effects. The non-invasive pulmonary drug administration provides the advantages of targeted-site delivery and avoids first-pass metabolism, which reduced the dose requirement and systemic adverse effects of the therapeutics. With the modification of the drugs with advanced carriers, the formulations may possess sustained released property, which helps in reducing the dosing frequency and enhanced patients’ compliances. The dry powder inhaler formulation is easy to handle and storage as it is relatively stable compared to liquids and suspension. This review mainly highlights the aerosolization properties of dry powder inhalable formulations with different anti-TB agents to understand and estimate the deposition manner of the drug in the lungs. Moreover, the safety profile of the novel dry powder inhaler formulations has been discussed. The results of the studies demonstrated that dry powder inhaler formulation has the potential in enhancing treatment efficacy.

Surface Composition and Aerosolization Stability of an Inhalable Combinational Powder Formulation Spray Dried Using a Three-Fluid Nozzle

PURPOSE

This study aims to understand the impact of spray drying nozzles on particle surface composition and aerosol stability.

METHODS

The combination formulations of colistin and azithromycin were formulated by 2-fluid nozzle (2 N) or 3-fluid (3 N) spray drying in a molar ratio of 1:1. A 3-factor, 2-level (2³) factorial design was selected to investigate effects of flow rate, inlet temperature and feed concentration on yield of spray drying and the performance of the spray dried formulations for the 3 N.

RESULTS

FPF values for the 2 N formulation (72.9 ± 1.9% for azithromycin & 73.4 ± 0.8% for colistin) were higher than those for the 3 N formulation (56.5 ± 3.8% for azithromycin & 55.1 ± 1.6% for colistin) when stored at 20% RH for 1 day, which could be attributed to smaller physical size for the 2 N. There was no change in FPF for both drugs in the 2 N formulation after storage at 75% RH for 90 days; however, there was a slight increase in FPF for colistin in the 3 N formulation at the same storage conditions. Surface enrichment of hydrophobic azithromycin was measured by X-ray photoelectron spectroscopy for both 2 N and 3 N formulations and interactions were studied using FTIR.

CONCLUSIONS

The 3-fluid nozzle provides flexibility in choosing different solvents and has the capability to spray dry at higher feed solid concentrations. This study highlights the impact of hydrophobic azithromycin enrichment on particle surface irrespective of the nozzle type, on the prevention of moisture-induced deterioration of FPF for hygroscopic colistin.

Optimization of inhalable liposomal powder formulations and evaluation of their in vitro drug delivery behavior in Calu-3 human lung epithelial cells

Inhalation therapy has advantages for the treatment of multidrug resistant bacterial lung infections with high drug concentrations at the infection sites in the airways and reduced systemic exposure. We have developed liposomal formulations for pulmonary delivery of synergistic ciprofloxacin (Cipro) and colistin (Col) as the potential candidate for treatment of lung infections caused by multidrug resistant Gram-negative bacteria. This study aims to: (1) further optimize the powder formulation by adding drying stabilizers (polyvinyl pyrrolidone or poloxamer) to protect the liposomes during spray-freeze-drying; (2) evaluate the transport and cellular uptake of drugs in a human lung epithelial Calu-3 cell model. The liposomal powder formulations were produced using the ultrasonic spray-freeze-drying technique. The optimal formulation (F5) used mannitol (8% w/v) and sucrose (2% w/v) as the internal lyoprotectants. Adding external lyoprotectants/aerosolization enhancers (i.e. 8% w/v mannitol, 2% w/v sucrose and 1%, w/w PVP 10) produced the superior rehydrated EE values of ciprofloxacin and colistin (50.2 ± 0.9% for Cipro and 37.8 ± 1.2% for Col) as well as satisfactory aerosol performance (FPF: 34.2 ± 0.8% for Cipro and 33.6 ± 0.9% for Col). The cytotoxicity study indicated that F5 with the colistin concentration at 50 μg/mL and ciprofloxacin at 200 μg/mL was not cytotoxic to human lung epithelial Calu-3 cells. The intracellular uptake of ciprofloxacin was concentration-dependent in Calu-3 cells and the uptake of A-B was more than that of B-A for all samples (p < 0.05). This study demonstrates that co-delivery of ciprofloxacin and colistin in a single liposome can lower the transport capability of both drugs across the Calu-3 cell monolayer and their accumulation in the cells. These findings indicate that co-loaded liposomal powder of ciprofloxacin and colistin is a promising potential treatment for respiratory infections caused by multidrug resistant Gram-negative bacteria.

Comparison between Colistin Sulfate Dry Powder and Solution for Pulmonary Delivery

To assess the difference in the fate of the antibiotic colistin (COLI) after its pulmonary delivery as a powder or a solution, we developed a COLI powder and evaluated the COLI pharmacokinetic properties in rats after pulmonary administration of the powder or the solution. The amorphous COLI powder prepared by spray drying was characterized by a mass median aerodynamic diameter and fine particle fraction of 2.68 ± 0.07 µm and 59.5 ± 5.4%, respectively, when emitted from a Handihaler^®. After intratracheal administration, the average pulmonary epithelial lining fluid (ELF): plasma area under the concentration versus time curves (AUC) ratios were 570 and 95 for the COLI solution and powder, respectively. However, the same COLI plasma concentration profiles were obtained with the two formulations. According to our pharmacokinetic model, this difference in ELF COLI concentration could be due to faster systemic absorption of COLI after the powder inhalation than for the solution. In addition, the COLI apparent permeability (P_app) across a Calu-3 epithelium model increased 10-fold when its concentration changed from 100 to 4000 mg/L. Based on this last result, we propose that the difference observed in vivo between the COLI solution and powder could be due to a high local ELF COLI concentration being obtained at the site where the dry particles impact the lung. This high local COLI concentration can lead to a local increase in COLI P_app, which is associated with a high concentration gradient and could produce a high local transfer of COLI across the epithelium and a consequent increase in the overall absorption rate of COLI.

Inhalable liposomal powder formulations for co-delivery of synergistic ciprofloxacin and colistin against multi-drug resistant gram-negative lung infections

The aim of this study was to design and characterize dry powder inhaler formulations of ciprofloxacin and colistin co-loaded liposomes prepared by the ultrasonic spray-freeze-drying (USFD) technique. Liposomal formulations and powder production parameters were optimized to achieve optimal characteristics and in-vitro performance such as encapsulation efficiency (EE), particle size, particle distribution index (PDI), fine particle fraction (FPF), emitted dose (ED) and in vitro antibacterial activity. The formulation (F6) with the mannitol (5% w/v) as the internal lyoprotectant and sucrose (5%, w/v), mannitol (10%, w/v) and leucine (5%, w/w) as the external lyoprotectants/aerosolization enhancers showed an optimal rehydrated EE values of ciprofloxacin and colistin (44.9 ± 0.9% and 47.0 ± 0.6%, respectively) as well as satisfactory aerosol performance (FPF: 45.8 ± 2.2% and 43.6 ± 1.6%, respectively; ED: 97.0 ± 0.5% and 95.0 ± 0.6%, respectively). For the blank liposomes, there was almost no inhibitory effect on the cell proliferation in human lung epithelial A549 cells, showing that the lipid materials used in the liposome formulation is safe for use in pulmonary drug delivery. The cytotoxicity study demonstrated that the optimized liposomal formulation (F6) was not cytotoxic at least at the drug concentrations of colistin 5 μg/mL and ciprofloxacin 20 μg/mL. Colistin (2 mg/L) monotherapy showed no antibacterial effect against P. aeruginosa H131300444 and H133880624. Ciprofloxacin (8 mg/L) monotherapy showed moderate bacterial killing for both clinical isolates; however, regrowth was observed in 6 h for P. aeruginosa H133880624. The liposomal formulation displayed superior antibacterial activity against clinical isolates of Pseudomonas aeruginosa H131300444 and P. aeruginosa H133880624 compared to each antibiotic per se. These results demonstrate that the liposomal powder formulation prepared by USFD could potentially be a pulmonary delivery system for antibiotic combination to treat multi-drug resistant Gram-negative lung infections.

Physical stability of dry powder inhaler formulations

Introduction: Dry powder inhalers (DPIs) are popular for pulmonary drug delivery. Various techniques have been employed to produce inhalation drug particles and improve the delivery efficiency of DPI formulations. Physical stability of these DPI formulations is critical to ensure the delivery of a reproducible dose to the airways over the shelf-life.Areas covered: This review focuses on the impact of solid-state stability on aerosolization performance of DPI drug particles manufactured by powder production approaches and particle-engineering techniques. It also highlights the different analytical tools that can be used to characterize the physical instability originating from production and storage.Expert opinion: A majority of the DPI literature focuses on the effects of physico-chemical properties such as size, morphology, and density on aerosolization. While little has been reported on the physical stability, particularly the stability of engineered drug particles for use in DPIs. Literature data have shown that different particle-engineering methods and storage conditions may cause physical instability of dry powders for inhalation and can significantly change the aerosol performance. A systematic examination of physical instability mechanisms in DPI formulations is necessary during formulation development in order to select the optimum formulation with satisfactory stability. In addition, the use of appropriate characterization tools is critical to detect and understand physical instability during the development of DPI formulations.

Simultaneous Particle Size Reduction and Homogeneous Mixing to Produce Combinational Powder Formulations for Inhalation by the Single-Step Co-Jet Milling

Homogeneous mixing of 2 cohesive jet-milled drug powders is a challenge for pharmaceutical manufacturing on account of their cohesive nature resulting in the formation of strong and random agglomerates. In this study, colistin and ciprofloxacin were co-jet milled to develop combinational antibiotic dry powder formulations for inhalation. The properties of particle size, morphology, content uniformity, and in vitro aerosolization were evaluated. The distribution of 2 drugs in the co-jet milled powders was assessed using time-of-flight-secondary ion mass spectrometry. The co-jet milled powders demonstrated an acceptable content uniformity indicating homogeneity. In general, time-of-flight-secondary ion mass spectrometry images showed relatively homogeneous distributions of ciprofloxacin and colistin in the co-milled formulations. Importantly, the 2 drugs generally had the similar fine particle fraction and deposition behavior in each combinational formulation supporting that the particle mixtures were relatively homogenous and could maximize the antimicrobial synergy. In conclusion, co-jet milling could be a viable technique to produce the combination powders for inhalation.

Treatment of metastatic lung cancer via inhalation administration of curcumin composite particles based on mesoporous silica

Curcumin attracted attention due to its promising anti-cancer properties and safety performance. However, its poor aqueous solubility and low bioavailability have to be overcome before it goes into clinic use. Here, porous composite particles are prepared by loading curcumin into mesoporous material SBA-15, and its therapeutic effect on lung cancer via inhalation administration have also been evaluated. The inclusion of curcumin in host material SBA-15 was confirmed by the reduced surface area and pore diameter of the composite material, and the aerodynamic performance of the composite material was investigated by FT-4 and NGI. Phagocytosis experiments on RAW264.7, the toxicity of material extracts on BEAS-2B cells, and the haemolysis experiments showed that the mesoporous materials had good biocompatibility at 10-400 μg/mL. The B16F10 melanoma metastatic lung mouse model was used to investigate the therapeutic effect of lung cancer after inhalable administration. It was found that the body weight of the curcumin composite particle-administered group decreased more slowly and the lung disease developed slower than the curcumin crude drug group, indicating that the composite particles has a certain inhibitory effect on tumours.

A Design of Experiment (DoE) approach to optimise spray drying process conditions for the production of trehalose/leucine formulations with application in pulmonary delivery

The present study evaluates the effect of L-leucine concentration and operating parameters of a laboratory spray dryer on characteristics of trehalose dry powders, with the goal of optimizing production of these powders for inhaled drug delivery. Trehalose/L-leucine mixtures were spray dried from aqueous solution using a laboratory spray dryer. A factorial design of experiment (DoE) was undertaken and process parameters adjusted were: inlet temperature, gas flow rate, feed solution flow rate (pump setting), aspiration setting and L-leucine concentration. Resulting powders were characterised in terms of particle size, yield, residual moisture content, and glass transition temperature. Particle size was mainly influenced by gas flow rate, whereas product yield and residual moisture content were found to be primarily affected by inlet temperature and spray solution feed rate respectively. Interactions between a number of different process parameters were elucidated, as were relationships between different responses. The leucine mass ratio influenced the physical stability of powders against environmental humidity, and a high leucine concentration (30% w/w) protected amorphous trehalose from moisture induced crystallization. High weight ratio of leucine in the formulation, however, negatively impacted the aerosol performance. Thus, in terms of L-leucine inclusion in a formulation designed for pulmonary delivery, a balance needs to be found between physical stability and deposition characteristics.

Effects of the antibiotic component on in-vitro bacterial killing, physico-chemical properties, aerosolization and dissolution of a ternary-combinational inhalation powder formulation of antibiotics for pan-drug resistant Gram-negative lung infections

Combinational antibiotic formulations have emerged as an important strategy to combat antibiotic resistance. The main objective of this study was to examine effects of individual components on the antimicrobial activity, physico-chemical properties, aerosolization and dissolution of powder aerosol formulations when three synergistic drugs were co-spray dried. A ternary dry powder formulation consisting of meropenem (75.5 %w/w), colistin (15.1 %w/w) and rifampicin (9.4 %w/w) at the selected ratio was produced by spray drying. The ternary formulation was characterized for in-vitro antibacterial activity, physico-chemical properties, surface composition, aerosol performance and dissolution. All of the formulations demonstrated excellent aerosolization behavior achieving a fine particle fraction of >70%, which was substantially higher than those for the Meropenem-SD and Colistin-Meropenem formulations. The results indicated that rifampicin controlled the surface morphology of the ternary and binary combination formulations resulting in the formation of highly corrugated particles. Advanced characterization of surface composition by XPS supported the hypothesis that rifampicin was enriched on the surface of the combination powder formulations. All spray-dried formulations were amorphous and absorbed substantial amount of water at the elevated humidity. Storage at the elevated humidity caused a substantial decline in aerosolization performance for the Meropenem-SD and Colistin-Meropenem, which was attributed to increased inter-particulate capillary forces or particle fusion. In contrast, the ternary combination and binary Meropenem-Rifampicin formulations showed no change in aerosol performance at the elevated storage humidity conditions; attributable to the enriched hydrophobicity of rifampicin on the particle surface that acted as a barrier against moisture condensation and particle fusion. Interestingly, in the ternary formulation rifampicin enrichment on the surface did not interfere with the dissolution of other two components (i.e. meropenem and colistin). Our study provides an insight on the impact of each component on the performance of co-spray dried combinational formulations.

Composite particle formulations of colistin and meropenem with improved in-vitro bacterial killing and aerosolization for inhalation

Antibiotic combination therapy is promising for the treatment of lower respiratory tract infections caused by multi-drug resistant Gram-negative pathogens. Inhaled antibiotic therapy offers the advantage of direct delivery of the drugs to the site of infection, as compared to the parenteral administrations. In this study, we developed composite particle formulations of colistin and meropenem. The formulations were characterized for particle size, morphology, specific surface area, surface chemical composition, in-vitro aerosolization performance and in-vitro antibacterial activity. The combinations demonstrated enhanced antibacterial activity against clinical isolates of Acinetobacter baumannii N16870 and Pseudomonas aeruginosa 19147, when compared with antibiotic monotherapy. Spray-dried meropenem alone showed a poor aerosolization performance as indicated by a low fine particle fraction (FPF) of 32.5 ± 3.3%. Co-spraying with colistin improved the aerosolization of meropenem with up to a two-fold increase in the FPF. Such improvements in aerosolization can be attributed to the enrichment of colistin on the surface of composite particles as indicated by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), and the increases in particle porosity. Intermolecular interactions between colistin and meropenem were observed for the combination formulations as measured by FT-IR. In conclusion, our results show that co-spray drying with colistin improves the antibacterial activity and aerosol performance of meropenem and produces a formulation with synergistic bacterial killing.

Improved Physical Stability and Aerosolization of Inhalable Amorphous Ciprofloxacin Powder Formulations by Incorporating Synergistic Colistin

This study aimed to develop dry powder inhaler (DPI) combination formulations of ciprofloxacin and colistin for use in respiratory infections. Effects of colistin on physical stability and aerosolization of spray-dried ciprofloxacin were examined. The combination DPI formulations were produced by co-spray drying colistin and ciprofloxacin in mass ratios of 1:1, 1:3, and 1:9. Colistin and ciprofloxacin were also co-sprayed with l-leucine in the mass ratio of 1:1:1. The physical and aerosolization stability of the selected co-sprayed formulations stored at 20, 55, and 75% relative humidity (RH) were examined. Formulation characterizations were carried out using powder X-ray diffraction (PXRD) for crystallinity, scanning electron microscopy for morphology and particle size distribution, and dynamic vapor sorption for moisture sorption. Particle surface analysis was performed using X-ray photoelectron spectroscopy, energy dispersive X-ray spectrometry, and nano-time-of-flight secondary ion mass spectrometry. Potential intermolecular interactions were studied using Fourier-transform infrared spectroscopy (FTIR). Aerosol performance was evaluated using a multistage liquid impinger with a RS01 monodose inhaler device. PXRD diffractograms showed that the co-spray-dried colistin-ciprofloxacin formulation in the mass ratio (1:1) was amorphous at 55% RH for up to 60 days; whereas the co-spray-dried colistin-ciprofloxacin (1:3) and colistin-ciprofloxacin (1:9) crystallized after storage for 3 days at 55% RH. However, the extent of crystallization for the combination formulations was less as compared to the spray-dried ciprofloxacin alone formulation. Surface morphology of the co-spray-dried formulations at different concentrations did not change even after storage at 55% RH for 60 days, unlike the spray-dried ciprofloxacin alone powder which became rougher after 3 days of storage at 55% RH. Surface analysis data indicated surface enrichment of colistin in the co-spray-dried formulations. Increasing colistin concentration on the composite particles surfaces improved aerosol performance of ciprofloxacin. FTIR data demonstrated intermolecular interactions between colistin and ciprofloxacin, thereby delaying and/or preventing crystallization of ciprofloxacin when co-spray-dried. Co-spray drying ciprofloxacin with colistin in the mass ratio (1:1) completely prevented crystallization of ciprofloxacin at 55% RH for up to 60 days. However, the colistin-ciprofloxacin formulation (1:1) began to fuse when stored at 75% RH due to moisture absorption resulting in a compromised aerosol performance. In contrast, the colistin-ciprofloxacin-leucine (1:1:1) formulation demonstrated no particle fusion, enabling a stable aerosol performance at 75% RH for 7 days. This study demonstrated that incorporation of colistin in the spray-dried formulations can improve physical stability and aerosolization of amorphous ciprofloxacin at 55% RH. At 75% RH, further addition of l-leucine in the formulation prevented particle fusion and deterioration in aerosol performance, attributed to the enrichment of nonhygroscopic l-leucine on the particle surface.

Influence of excipients on physical and aerosolization stability of spray dried high-dose powder formulations for inhalation

The aim of this study is to investigate the influence of excipients on physical and aerosolization stability of spray dried Ciprofloxacin dry powder inhaler formulations. The model drug, Ciprofloxacin hydrochloride, was co-spray dried with excipients such as disaccharides (sucrose, lactose, trehalose), mannitol and l-leucine. The spray dried samples were stored at two different relative humidity (RH) conditions of: (1) 20% and (2) 55% RH at 20 °C. Ciprofloxacin co-spray dried with disaccharides and l-leucine in the mass ratio of 1:1 demonstrated an increase in fine particle fraction (FPF) as compared with the spray dried Ciprofloxacin alone when stored at 20% RH. However, deterioration in FPF of Ciprofloxacin co-spray dried with disaccharide and mannitol was observed upon storage at 55% RH as compared to the corresponding formulations stored at 20% RH due to particle agglomeration. Whereas, 10% and 50% w/w l-leucine in the formulation showed no change in aerosol performance (FPF of 71.1 ± 3.5% and 79.5 ± 3.1%, respectively) when stored at 55% RH for 10 days as compared to 20% RH (FPF of 68.1 ± 0.3% and 73.6 ± 7.1%, respectively). l-Leucine demonstrated aerosolization stability by alleviating crystallization of Ciprofloxacin to some extent and preventing significant change in particle morphology. l-Leucine is well-recognized as aerosolization enhancer; our study has shown l-leucine is also a physical and aerosolization stabilizer for spray dried Ciprofloxacin DPI formulations. Such stability enhancing activities were attributed to the enrichment of l-leucine on the particle surface as confirmed by XPS data, and intermolecular interactions between l-leucine and Ciprofloxacin as measured by FT-IR.

Effects of Moisture-Induced Crystallization on the Aerosol Performance of Spray Dried Amorphous Ciprofloxacin Powder Formulations

PURPOSE

This study aims to investigate the influence of different storage humidity conditions on crystallization and aerosol performance of inhalable spray dried amorphous powder formulations (Ciprofloxacin hydrochloride as the model drug).

METHODS

The spray dried samples were stored at 20%, 55% and 75% relative humidity (RH). Crystallinity was monitored by Powder X-ray diffraction (PXRD), and particle morphology was measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Aerosol performance was evaluated using a multi-stage liquid impinger (MSLI).

RESULTS

PXRD diffractograms showed the spray dried Ciprofloxacin stored at 20% RH for three weeks were amorphous; whereas those stored at 55% RH and 75% RH started crystallizing after one hour. Fine particle fraction (FPF) of the particles was improved from 28% to 42% after storage at 55% RH for three days. Such improvement was attributed to the crystallization of amorphous powders, which led to increased particle roughness and reduced particulate contact area, as visualized by SEM and quantified by AFM. A linear relationship was observed between degree of crystallinity/crystallite size and FPF (R2 = 0.94 and R2 = 0.96, respectively). However, deterioration in aerosol performance was observed after storage at 75% RH due to formation of inter-particulate liquid/solid bridges, as confirmed by SEM.

CONCLUSIONS

This study provides a fundamental understanding in moisture-induced physical and aerosol instability of the spray dried powder formulations.

Pulmonary Pharmacokinetics of Colistin following Administration of Dry Powder Aerosols in Rats

Colistin has been administered via nebulization for the treatment of respiratory tract infections. Recently, dry powder inhalation (DPI) has attracted increasing attention. The current study aimed to investigate the pharmacokinetics (PK) of colistin in epithelial lining fluid (ELF) and plasma following DPI and intravenous (i.v.) administration in healthy Sprague-Dawley rats. Rats were given colistin as DPI intratracheally (0.66 and 1.32 mg base/kg of body weight) or i.v. injection (0.66 mg base/kg). Histopathological examination of lung tissue was performed at 24 h. Colistin concentrations in both ELF and plasma were quantified, and a population PK model was developed and compared to a previously published PK model of nebulized colistin in rats. A two-compartment structural model was developed to describe the PK of colistin in both ELF and plasma following pulmonary or i.v. administration. The model-estimated clearance from the central plasma compartment was 0.271 liter/h/kg (standard error [SE] = 2.51%). The transfer of colistin from the ELF compartment to the plasma compartment was best described by a first-order rate constant (clearance of colistin from the ELF compartment to the plasma compartment = 4.03 × 10^-4 liter/h/kg, SE = 15%). DPI appeared to have a higher rate of absorption (time to the maximum concentration in plasma after administration of colistin by DPI, ≤10 min) than nebulization (time to the maximum concentration in plasma after administration of colistin by nebulization, 20 to 30 min), but the systemic bioavailabilities by the two routes of administration were similar (∼46.5%, SE = 8.43%). Histopathological examination revealed no significant differences in inflammation in lung tissues between the two treatments. Our findings suggest that colistin DPI is a promising alternative to nebulization considering the similar PK and safety profiles of the two forms of administration. The PK and histopathological information obtained is critical for the development of optimal aerosolized colistin regimens with activity against lung infections caused by Gram-negative bacteria.

The Delivery of High-Dose Dry Powder Antibiotics by a Low-Cost Generic Inhaler

The routine of loading multiple capsules for delivery of high-dose antibiotics is time consuming, which may reduce patient adherence to inhaled treatment. To overcome this limitation, an investigation was carried out using four modified versions of the Aerolizer® that accommodate a size 0 capsule for delivery of high payload formulations. In some prototypes, four piercing pins of 0.6 mm each were replaced with a single centrally located 1.2-mm pin and one-third reduced air inlet of the original design. The performance of these inhalers was evaluated using spray-dried antibiotic powders with distinct morphologies: spherical particles with a highly corrugated surface (colistin and tobramycin) and needle-like particles (rifapentine). The inhalers were tested at capsule loadings of 50 mg (colistin), 30 mg (rifapentine) and 100 mg (tobramycin) using a multistage liquid impinger (MSLI) operating at 60 L/min. The device with a single pin and reduced air inlet showed a superior performance than the other prototypes in dispersing colistin and rifapentine powders, with a fine particle fraction (FPF wt% <5 μm in the aerosol) between 62 and 68%. Subsequently, an Aerolizer® with the same configuration (single pin and one-third air inlet) that accommodates a size 00 capsule was designed to increase the payload of colistin and rifapentine. The performance of the device at various inspiratory flow rates and air volumes achievable by most cystic fibrosis (CF) patients was examined at the maximum capsule loading of 100 mg. The device showed optimal performance at 45 L/min with an air volume of 1.5-2.0 L for colistin and 60 L/min with an air volume of 2.0 L for rifapentine. In conclusion, the modified size 00 Aerolizer® inhaler as a low-cost generic device demonstrated promising results for delivery of various high-dose formulations for treatment of lung infections.

How Much Surface Coating of Hydrophobic Azithromycin Is Sufficient to Prevent Moisture-Induced Decrease in Aerosolisation of Hygroscopic Amorphous Colistin Powder?

Aerosolisation performance of hygroscopic particles of colistin could be compromised at elevated humidity due to increased capillary forces. Co-spray drying colistin with a hydrophobic drug is known to provide a protective coating on the composite particle surfaces against moisture-induced reduction in aerosolisation performance; however, the effects of component ratio on surface coating quality and powder aerosolisation at elevated relative humidities are unknown. In this study, we have systematically examined the effects of mass ratio of hydrophobic azithromycin on surface coating quality and aerosolisation performance of the co-spray dried composite particles. Four combination formulations with varying drug ratios were prepared by co-spray drying drug solutions. Both of the drugs in each combination formulation had similar in vitro deposition profiles, suggesting that each composite particle comprises two drugs in the designed mass ratio, which is supported by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) data. XPS and ToF-SIMS measurements also revealed that 50% by weight (or 35% by molecular fraction) of azithromycin in the formulation provided a near complete coating of 96.5% (molar fraction) on the composite particle surface, which is sufficient to prevent moisture-induced reduction in fine particle fraction (FPF)recovered and FPFemitted. Higher azithromycin content did not increase coating coverage, while contents of azithromycin lower than 20% w/w did not totally prevent the negative effects of humidity on aerosolisation performance. This study has highlighted that a critical amount of azithromycin is required to sufficiently coat the colistin particles for short-term protection against moisture.

Amorphous powders for inhalation drug delivery

For inhalation drug delivery, amorphous powder formulations offer the benefits of increased bioavailability for poorly soluble drugs, improved biochemical stability for biologics, and expanded options of using various drugs and their combinations. However, amorphous formulations usually have poor physicochemical stability. This review focuses on inhalable amorphous powders, including the production methods, the active pharmaceutical ingredients and the excipients with a highlight on stabilization of the particles.

L-Leucine as an excipient against moisture on in vitro aerosolization performances of highly hygroscopic spray-dried powders

L-Leucine (LL) has been widely used to enhance the dispersion performance of powders for inhalation. LL can also protect powders against moisture, but this effect is much less studied. The aim of this study was to investigate whether LL could prevent moisture-induced deterioration in in vitro aerosolization performances of highly hygroscopic spray-dried powders. Disodium cromoglycate (DSCG) was chosen as a model drug and different amounts of LL (2-40% w/w) were added to the formulation, with the aim to explore the relationship between powder dispersion, moisture protection and physicochemical properties of the powders. The powder formulations were prepared by spray drying of aqueous solutions containing known concentrations of DSCG and LL. The particle sizes were measured by laser diffraction. The physicochemical properties of fine particles were characterized by X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic vapor sorption (DVS). The surface morphology and chemistry of fine particles were analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In vitro aerosolization performances were evaluated by a next generation impactor (NGI) after the powders were stored at 60% or 75% relative humidity (RH), and 25°C for 24h. Spray-dried (SD) DSCG powders were amorphous and absorbed 30-45% (w/w) water at 70-80% RH, resulting in deterioration in the aerosolization performance of the powders. LL did not decrease the water uptake of DSCG powders, but it could significantly reduce the effect of moisture on aerosolization performances. This is due to enrichment of crystalline LL on the surface of the composite particles. The effect was directly related to the percentage of LL coverage on the surface of particles. Formulations having 61-73% (molar percent) of LL on the particle surface (which correspond to 10-20% (w/w) of LL in the bulk powders) could minimize moisture-induced deterioration in the aerosol performance. In conclusion, particle surface coverage of LL can offer short-term protection against moisture on dispersion of hygroscopic powders.

Investigation of the Changes in Aerosolization Behavior Between the Jet-Milled and Spray-Dried Colistin Powders Through Surface Energy Characterization

This study aimed to investigate the surface energy factors behind improved aerosolization performance of spray-dried colistin powder formulations compared with those produced by jet milling. Inhalable colistin powder formulations were produced by jet milling or spray drying (with or without l-leucine). Scanning electron micrographs showed the jet-milled particles had irregularly angular shapes, whereas the spray-dried particles were more spherical. Significantly higher fine particle fractions were measured for the spray-dried (43.8%-49.6%) versus the jet-milled formulation (28.4%) from a Rotahaler at 60 L/min; albeit the size distribution of the jet-milled powder was smaller. Surprisingly, addition of l-leucine in the spray drying feed solution gave no significant improvement in fine particle fraction. As measured by inverse gas chromatography, spray-dried formulations had significantly (p < 0.001) lower dispersive, specific, and total surface energy values and more uniform surface energy distributions than the jet-milled powder. Interestingly, no significant difference was measured in the specific and total surface energy values between the spray-dried formulation with or without l-leucine. Based on our previous findings in the self-assembling behavior of colistin in aqueous solution and the surface energy data obtained here, we propose the self-assembly of colistin molecules during spray drying contributed significantly to the reduction of surface free energy and the superior aerosolization performance.

Effects of Surface Composition on the Aerosolisation and Dissolution of Inhaled Antibiotic Combination Powders Consisting of Colistin and Rifampicin

Colistin is often the only effective antibiotic against the respiratory infections caused by multidrug-resistant Gram-negative bacteria. However, colistin-resistant multidrug-resistant isolates have been increasingly reported and combination therapy is preferred to combat resistance. In this study, five combination formulations containing colistin (COL) and rifampicin (RIF) were prepared by spray drying. The lowest minimum inhibitory concentration (MIC) value against Pseudomonas aeruginosa PAO1 was measured for the formulation of COL/RIF = 4:1 with relatively high emitted doses (over 80%) and satisfactory fine particle fractions (over 60%). Data from X-ray photoelectron spectroscopy (XPS) and nano-time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed the surfaces of particles were mainly covered by rifampicin even for the formulation with a mass ratio of COL/RIF = 4:1. Because colistin is hygroscopic and rifampicin is hydrophobic, moisture absorption of combination formulations was significantly lower than the pure colistin formulation in the dynamic vapour sorption results. To investigate the dissolution characteristics, four dissolution test methods (diffusion Franz cell, modified Franz cell, flow-through and beaker methods) were employed and compared. The modified Franz cell method was selected to test the dissolution behaviour of aerosolised powder formulations to eliminate the effect of membrane on dissolution. The results showed that surface enrichment of hydrophobic rifampicin neither affected aerosolisation nor retarded dissolution rate of colistin in the combination formulations. For the first time, advanced surface characterisation techniques of XPS and ToF-SIMS have shown their capability to understand the effect of surface composition on the aerosolisation and dissolution of combination powders.

Inhaled anti-infective chemotherapy for respiratory tract infections: successes, challenges and the road ahead

One of the most common causes of illnesses in humans is from respiratory tract infections caused by bacterial, viral or fungal pathogens. Inhaled anti-infective drugs are crucial for the prophylaxis and treatment of respiratory tract infections. The benefit of anti-infective drug delivery via inhalation is that it affords delivery of sufficient therapeutic dosages directly to the primary site of infection, while minimizing the risks of systemic toxicity or avoiding potential suboptimal pharmacokinetics/pharmacodynamics associated with systemic drug exposure. This review provides an up-to-date treatise of approved and novel developmental inhaled anti-infective agents, with particular attention to effective strategies for their use, pulmonary pharmacokinetic properties and safety.

Inhaled formulations and pulmonary drug delivery systems for respiratory infections

Respiratory infections represent a major global health problem. They are often treated by parenteral administrations of antimicrobials. Unfortunately, systemic therapies of high-dose antimicrobials can lead to severe adverse effects and this calls for a need to develop inhaled formulations that enable targeted drug delivery to the airways with minimal systemic drug exposure. Recent technological advances facilitate the development of inhaled anti-microbial therapies. The newer mesh nebulisers have achieved minimal drug residue, higher aerosolisation efficiencies and rapid administration compared to traditional jet nebulisers. Novel particle engineering and intelligent device design also make dry powder inhalers appealing for the delivery of high-dose antibiotics. In view of the fact that no new antibiotic entities against multi-drug resistant bacteria have come close to commercialisation, advanced formulation strategies are in high demand for combating respiratory 'super bugs'.

Advances in device and formulation technologies for pulmonary drug delivery

Inhaled pharmaceuticals are formulated and delivered differently according to the therapeutic indication. However, specific device-formulation coupling is often fickle, and new medications or indications also demand new strategies. The discontinuation of chlorofluorocarbon propellants has seen replacement of older metered dose inhalers with dry powder inhaler formulations. High-dose dry powder inhalers are increasingly seen as an alternative dosage form for nebulised medications. In other cases, new medications have completely bypassed conventional inhalers and been formulated for use with unique inhalers such as the Staccato® device. Among these different devices, integration of software and electronic assistance has become a shared trend. This review covers recent device and formulation advances that are forming the current landscape of inhaled therapeutics.

Emerging inhalation aerosol devices and strategies: where are we headed?

Novel inhaled therapeutics including antibiotics, vaccines and anti-hypertensives, have led to innovations in designing suitable delivery systems. These emerging design technologies are in urgent demand to ensure high aerosolisation performance, consistent efficacy and satisfactory patient adherence. Recent vibrating-mesh and software technologies have resulted in nebulisers that have remarkably accurate dosing and portability. Alternatively, dry powder inhalers (DPIs) have become highly favourable for delivering high-dose and single-dose drugs with the aid of advanced particle engineering. In contrast, innovations are needed to overcome the technical constrains in drug-propellant incompatibility and delivering high-dose drugs with pressurised metered dose inhalers (pMDIs). This review discusses recent and emerging trends in pulmonary drug delivery systems.

Technological and practical challenges of dry powder inhalers and formulations

In the 50 years following the introduction of the first dry powder inhaler to the market, several developments have occurred. Multiple-unit dose and multi-dose devices have been introduced, but first generation capsule inhalers are still widely used for new formulations. Many new particle engineering techniques have been developed and considerable effort has been put in understanding the mechanisms that control particle interaction and powder dispersion during inhalation. Yet, several misconceptions about optimal inhaler performance manage to survive in modern literature. It is, for example still widely believed that a flow rate independent fine particle fraction contributes to an inhalation performance independent therapy, that dry powder inhalers perform best at 4 kPa (or 60 L/min) and that a high resistance device cannot be operated correctly by patients with reduced lung function. Nevertheless, there seems to be a great future for dry powder inhalation. Many new areas of interest for dry powder inhalation are explored and with the assistance of new techniques like computational fluid dynamics and emerging particle engineering technologies, this is likely to result in a new generation of inhaler devices and formulations, that will enable the introduction of new therapies based on inhaled medicines.

Synergistic antibiotic combination powders of colistin and rifampicin provide high aerosolization efficiency and moisture protection

For many respiratory infections caused by multidrug-resistant Gram-negative bacteria, colistin is the only effective antibiotic despite its nephrotoxicity. A novel inhaled combination formulation of colistin with a synergistic antimicrobial component of rifampicin was prepared via co-spray drying, aiming to deliver the drug directly to the respiratory tract and minimize drug resistance and adverse effects. Synergistic antibacterial activity against Acinetobacter baumannii was demonstrated for the combination formulation with high emitted doses (96%) and fine particle fraction total (FPFtotal; 92%). Storage of the spray-dried colistin alone formulation in the elevated relative humidity (RH) of 75% resulted in a substantial deterioration in the aerosolization performance because the amorphous colistin powders absorbed significant amount of water up to 30% by weight. In contrast, the FPFtotal values of the combination formulation stored at various RH were unchanged, which was similar to the aerosolization behavior of the spray-dried rifampicin-alone formulation. Advanced surface chemistry measurements by XPS and ToF-SIMS demonstrated a dominance of rifampicin on the combination particle surfaces, which contributed to the moisture protection at the elevated RH. This study shows a novel inhalable powder formulation of antibiotic combination with the combined beneficial properties of synergistic antibacterial activity, high aerosolization efficiency, and moisture protection.