Efficacy of liposome-encapsulated ciprofloxacin in a murine model of Q fever

Essential considerations towards development of effective nasal antibiotic formulation: features, strategies, and future directions

INTRODUCTION

Intranasal antibiotic products are gaining popularity as a promising method of administering antibiotics, which provide numerous benefits, e.g. enhancing drug bioavailability, reducing adverse effects, and potentially minimizing resistance threats. However, some issues related to the antibiotic substances and nasal route challenges must be addressed to prepare effective formulations.

AREAS COVERED

This review focuses on the valuable points of nasal delivery as an alternative route for administering antibiotics, coupled with the challenges in the nasal cavity that might affect the formulations. Moreover, this review also highlights the application of nasal delivery to introduce antibiotics for local therapy, brain targeting, and systemic effects that have been conducted. In addition, this viewpoint provides strategies to maintain antibiotic stability and several crucial aspects to be considered for enabling effective nasal formulation.

EXPERT OPINION

In-depth knowledge and understanding regarding various key considerations with respect to the antibiotic substances and nasal route delivery requirement in preparing effective nasal antibiotic formulation would greatly improve the development of nasally administered antibiotic products, enabling better therapeutic outcomes of antibiotic treatment and establishing appropriate use of antibiotics, which in turn might reduce the chance of antibiotic resistance and enhance patient comfort.

Evaluation of Alternative Doxycycline Antibiotic Regimes in an Inhalational Murine Model of Q Fever

The timing of the initiation of antibiotic treatment has been shown to impact the clinical outcome of many bacterial infections, including Q fever. Delayed, suboptimal or incorrect antibiotic treatment has been shown to result in poor prognosis, resulting in the progression of acute disease to long-term chronic sequalae. Therefore, there is a requirement to identify an optimal, effective therapeutic regimen to treat acute Q fever. In the study, the efficacies of different doxycycline monohydrate regimens (pre-exposure prophylaxis, post-exposure prophylaxis or treatment at symptom onset or resolution) were evaluated in an inhalational murine model of Q fever. Different treatment lengths (7 or 14 days) were also evaluated. Clinical signs and weight loss were monitored during infection and mice were euthanized at different time points to characterize bacterial colonization in the lungs and the dissemination of bacteria to other tissues including the spleen, brain, testes, bone marrow and adipose. Post-exposure prophylaxis or doxycycline treatment starting at symptoms onset reduced clinical signs, and also delayed the systemic clearance of viable bacteria from key tissues. Effective clearance was dependent on the development of an adaptive immune response, but also driven by sufficient bacterial activity to maintain an active immune response. Pre-exposure prophylaxis or post-exposure treatment at the resolution of clinical signs did not improve outcomes. These are the first studies to experimentally evaluate different doxycycline treatment regimens for Q fever and illustrate the need to explore the efficacy of other novel antibiotics.

Finafloxacin, a Novel Fluoroquinolone, Reduces the Clinical Signs of Infection and Pathology in a Mouse Model of Q Fever

Finafloxacin is a novel fluoroquinolone with optimal antibacterial activity in low pH environments, therefore offering a therapeutic advantage over some traditional antibiotics, in treating bacterial infections associated with acidic foci. Coxiella burnetii, the causative agent of Q fever, is a bacterium which resides and replicates in acidic intracellular parasitic vacuoles. The efficacy of finafloxacin was evaluated in vivo using the A/J mouse model of inhalational Q fever and was compared to doxycycline, the standard treatment for this infection and ciprofloxacin, a comparator fluoroquinolone. Finafloxacin reduced the severity of the clinical signs of infection and weight loss associated with Q fever, but did not reduce the level of bacterial colonization in tissues compared to doxycycline or ciprofloxacin. However, histopathological analysis suggested that treatment with finafloxacin reduced tissue damage associated with C. burnetii infection. In addition, we report for the first time, the use of viable counts on axenic media to evaluate antibiotic efficacy in vivo.

Intracellular Activity of Antibiotics against Coxiella burnetii in a Model of Activated Human THP-1 Cells

We evaluated antibiotic activity against the intracellular bacterium Coxiella burnetii using an activated THP-1 cell model of infection. At clinically relevant concentrations, the intracellular bacterial load was reduced 300-fold by levofloxacin and finafloxacin, 40-fold by doxycycline, and 4-fold by ciprofloxacin and was unaffected by azithromycin. Acidification of the culture medium reduced antibiotic activity, with the exceptions of doxycycline (no change) and finafloxacin (slight improvement). This model may be used to select antibiotics to be evaluated in vivo.

Evaluation of the Efficacy of Doxycycline, Ciprofloxacin, Levofloxacin and Co-trimoxazole using in vitro and in vivo models of Q fever

Q fever, caused by the intracellular pathogen Coxiella burnetii, is traditionally treated using tetracycline antibiotics, such as doxycycline. Doxycycline is often poorly tolerated and antibiotic resistant strains have been isolated. In this study, we have evaluated a panel of antibiotics (doxycycline, ciprofloxacin, levofloxacin, and, co-trimoxazole) against C. burnetii using in vitro methods (determination of MIC using liquid and solid media; efficacy assessment in a THP cell infection model) and in vivo methods (wax moth larvae and mouse models of infection). In addition, the schedule for antibiotic treatment has been evaluated, with therapy initiated at 24 h pre or post challenge. Both doxycycline and levofloxacin limited overt clinical signs during treatment in the AJ mouse model of aerosol infection, but further studies are required to investigate the possibility of disease relapse or incomplete bacterial clearance after the antibiotics are stopped. Levofloxacin was well tolerated and therefore warrants further investigation as an alternative to the current recommended treatment with doxycycline.

A macrophage-targeted platform for extending drug dosing with polymer prodrugs for pulmonary infection prophylaxis

Pulmonary melioidosis is a bacterial disease with high morbidity and a mortality rate that can be as high as 40% in resource-poor regions of South Asia. This disease burden is linked to the pathogen's intrinsic antibiotic resistance and protected intracellular localization in alveolar macrophages. Current treatment regimens require several antibiotics with multi-month oral and intravenous administrations that are difficult to implement in under-resourced settings. Herein, we report that a macrophage-targeted polyciprofloxacin prodrug acts as a surprisingly effective pre-exposure prophylactic in highly lethal murine models of aerosolized human pulmonary melioidosis. A single dose of the polymeric prodrug maintained high lung drug levels and targeted an intracellular depot of ciprofloxacin to the alveolar macrophage compartment that was sustained over a period of 7 days above minimal inhibitory concentrations. This intracellular pharmacokinetic profile provided complete pre-exposure protection in a BSL-3 model with an aerosolized clinical isolate of Burkholderia pseudomallei from Thailand. This total protection was achieved despite the bacteria's relative resistance to ciprofloxacin and where an equivalent dose of pulmonary-administered ciprofloxacin was ineffective. For the first time, we demonstrate that targeting the intracellular macrophage compartment with extended antibiotic dosing can achieve pre-exposure prophylaxis in a model of pulmonary melioidosis. This fully synthetic and modular therapeutic platform could be an important therapeutic approach with new or re-purposed antibiotics for melioidosis prevention and treatment, especially as portable inhalation devices in high-risk, resource-poor settings.

A Novel Marmoset (Callithrix jacchus) Model of Human Inhalational Q Fever

Common marmosets (Callithrix jacchus) were shown to be susceptible to inhalational infection with Coxiella burnetii, in a dose-dependent manner, producing a disease similar to human Q fever, characterized by a resolving febrile response. Illness was also associated with weight loss, liver enzyme dysfunction, characteristic cellular activation, circulating INF-γ and bacteraemia. Viable C. burnetii was recovered from various tissues during disease and from 75% of the animal's lungs on 28 days post challenge, when there were no overt clinical features of disease but there was histological evidence of macrophage and lymphocyte infiltration into the lung resulting in granulomatous alveolitis. Taken together, these features of disease progression, physiology and bacterial spread appear to be consistent with human disease and therefore the common marmoset can be considered as a suitable model for studies on the pathogenesis or the development of medical counter measures of inhalational Q fever.

In vitro and in vivo antibacterial activity of nitrofurantoin against clinical isolates of E. coli in Japan and evaluation of biological cost of nitrofurantoin resistant strains using a mouse urinary tract infection model

INTRODUCTION

Nitrofurantoin is a well-established antibiotic, and is an important first-line oral treatment for uncomplicated urinary tract infections. However, little information is available with respect to its antibacterial activity in Japan, in vivo efficacy, or the in vivo biological cost of resistant strains.

METHODS

We compared the susceptibility of six representative antibacterial agents-nitrofurantoin, sulfamethoxazole/trimethoprim, fosfomycin, mecillinam, ciprofloxacin, and cefdinir-against E. coli clinically isolated in Japan during 2017. We evaluated the in vivo efficacy of nitrofurantoin using a model of mouse urinary tract infection caused by ciprofloxacin resistant E. coli. We obtained nitrofurantoin resistant isolates through tests generating spontaneous mutations, and assessed the in vivo fitness of nitrofurantoin resistant isolates.

RESULTS

The MIC₉₀ of nitrofurantoin was 16 μg/mL, and was the lowest among the drugs tested. It was found that, in the mouse urinary tract infection model, 30 mg/kg and 100 mg/kg of nitrofurantoin reduced the count of viable bacterial cells in the kidney, while 100 mg/kg of ciprofloxacin did not. All spontaneous bacterial mutants resistant to nitrofurantoin had deletions in the nfsA gene, and we found that the resistant strain had lower growth in the mouse urinary tract infection model than in the parent strain.

CONCLUSIONS

We demonstrated promising in vitro and in vivo activity of nitrofurantoin against E. coli clinical isolates in Japan, and lower in vivo fitness of the resistant strain of nitrofurantoin.

Pharmacokinetics of Free Oxytetracycline and Oxytetracycline Loaded Cockle Shell Calcium Carbonate-Based Nanoparticle in BALB/c Mice

The development and utilization of nano-antibiotics is currently gaining attention as a possible solution to antibiotic resistance. The aim of this study was therefore to determine the pharmacokinetics of free oxytetracycline (OTC) and oxytetracycline loaded cockle shell calcium carbonate-based nanoparticle (OTC-CNP) after a single dose of intraperitoneal (IP) administration in BALB/c mice. A total of 100 female BALB/c mice divided into two groups of equal number (n = 50) were administered with 10 mg/kg OTC and OTC-CNP, respectively. Blood samples were collected before and post-administration from both groups at time 0, 5, 10, 15, and 30 min and 1, 2, 6, 24, and 48 h, and OTC plasma concentration was quantified using a validated HPLC-UV method. The pharmacokinetic parameters were analyzed using a non-compartment model. The C _max values of OTC in OTC-CNP and free OTC treated group were 64.99 and 23.53 μg/ml, respectively. OTC was detected up to 24 h in the OTC-CNP group as against 1 h in the free OTC group following intraperitoneal administration. In the OTC-CNP group, the plasma elimination rate of OTC was slower while the half-life, the area under the curve, and the volume of the distribution were increased. In conclusion, the pharmacokinetic profile of OTC in the OTC-CNP group differs significantly from that of free OTC. However, further studies are necessary to determine the antibacterial efficacy of OTC-CNP for the treatment of bacterial diseases.

Control of the Lung Residence Time of Highly Permeable Molecules after Nebulization: Example of the Fluoroquinolones

Pulmonary drug delivery is a promising strategy to treat lung infectious disease as it allows for a high local drug concentration and low systemic side effects. This is particularly true for low-permeability drugs, such as tobramycin or colistin, that penetrate the lung at a low rate after systemic administration and greatly benefit from lung administration in terms of the local drug concentration. However, for relatively high-permeable drugs, such as fluoroquinolones (FQs), the rate of absorption is so high that the pulmonary administration has no therapeutic advantage compared to systemic or oral administration. Formulation strategies have thus been developed to decrease the absorption rate and increase FQs’ residence time in the lung after inhalation. In the present review, some of these strategies, which generally consist of either decreasing the lung epithelium permeability or decreasing the release rate of FQs into the epithelial lining fluid after lung deposition, are presented in regards to their clinical aspects.

Evaluation of liposomal ciprofloxacin formulations in a murine model of anthrax

The in vivo efficacy of liposomal encapsulated ciprofloxacin in two formulations, lipoquin and apulmiq, were evaluated against the causative agent of anthrax, Bacillus anthracis. Liposomal encapsulated ciprofloxacin is attractive as a therapy since it allows for once daily dosing and achieves higher concentrations of the antibiotic at the site of initial mucosal entry but lower systemic drug concentrations. The in vivo efficacy of lipoquin and apulmiq delivered by intranasal instillation was studied at different doses and schedules in both a post exposure prophylaxis (PEP) therapy model and in a delayed treatment model of murine inhalational anthrax. In the mouse model of infection, the survival curves for all treatment cohorts differed significantly from the vehicle control. Ciprofloxacin, lipoquin and apulmiq provided a high level of protection (87-90%) after 7 days of therapy when administered within 24 hours of exposure. Reducing therapy to only three days still provided protection of 60-87%, if therapy was provided within 24 hours of exposure. If treatment was initiated 48 hours after exposure the survival rate was reduced to 46-65%. These studies suggest that lipoquin and apulmiq may be attractive therapies as PEP and as part of a treatment cocktail for B. anthracis.

Pathologic changes and immune responses against Coxiella burnetii in mice following infection via non-invasive intratracheal inoculation

Q fever is a worldwide zoonosis caused by Coxiella burnetii. Human Q fever is typically acquired through inhalation of contaminated aerosols, resulting in an initial pulmonary infection. In this study, BALB/c mice were infected with C. burnetii via an intratracheal (IT) route using a non-invasive aerosol pulmonary delivery device to directly place the living C. burnetii organisms into the lungs of the mice. The bacterial loads, pathological lesions, and antibody and cellular responses were analyzed and compared with those of mice infected via an intraperitoneal (IP) route. Compared with mice infected via an IP route, mice infected via an IT route exhibited a higher bacterial load and more severe pathological lesions in the heart and lungs at days 3 and 7 post-infection (pi). The levels of interferon-γ and IL-12p70 in the serum of mice infected via the IT route were significantly higher than those of mice infected via the IP route at day 3 pi. In conclusion, this murine model of acute C. burnetii infection via IT inoculation closely resembles the natural route of C. burnetii infection than that of IP injection. Thus, this newly developed model will be useful for investigating the pathogenesis and immunity of C. burnetii aerosol infection, as well as for the evaluation of therapeutic drugs and preventive vaccines of Q fever.

From cell culture to cynomolgus macaque: infection models show lineage-specific virulence potential of Coxiella burnetii

Coxiella burnetii is an obligate intracellular pathogen that causes the zoonotic disease Q fever in humans, which can occur in either an acute or a chronic form with serious complications. The bacterium has a wide host range, including unicellular organisms, invertebrates, birds and mammals, with livestock representing the most significant reservoir for human infections. Cell culture models have been used to decipher the intracellular lifestyle of C. burnetii, and several infection models, including invertebrates, rodents and non-human primates, are being used to investigate host-pathogen interactions and to identify bacterial virulence factors and vaccine candidates. However, none of the models replicate all aspects of human disease. Furthermore, it is becoming evident that C. burnetii isolates belonging to different lineages exhibit differences in their virulence in these models. Here, we compare the advantages and disadvantages of commonly used infection models and summarize currently available data for lineage-specific virulence.

Comparison of PCR and Viable Count as a Method for Enumeration of Bacteria in an A/J Mouse Aerosol Model of Q Fever

Historically, disease progression in animal models of Q fever has been carried out using PCR to monitor the presence of Coxiella burnetii DNA in the host. However, the colonization and dissemination of other bacterial infections in animal models are tracked using viable counts, enabling an accurate assessment of viable bacterial load within tissues. Following recent advances in the culture methods, it has become possible to do the same with C. burnetii. Here we compare and contrast the different information gained by using PCR or viable counts to study this disease. Viable bacteria were cleared from organs much faster than previously reported when assessed by bacterial DNA, but weight loss and clinical signs improved while animals were still heavily infected.

Temperature-sensitive liposomal ciprofloxacin for the treatment of biofilm on infected metal implants using alternating magnetic fields

Implants are commonly used as a replacement for damaged tissue. Many implants, such as pacemakers, chronic electrode implants, bone screws, and prosthetic joints, are made of or contain metal. Infections are one of the difficult to treat complications associated with metal implants due to the formation of biofilm, a thick aggregate of extracellular polymeric substances (EPS) produced by the bacteria. In this study, we treated a metal prosthesis infection model using a combination of ciprofloxacin-loaded temperature-sensitive liposomes (TSL) and alternating magnetic fields (AMF). AMF heating is used to disrupt the biofilm and release the ciprofloxacin-loaded TSL. The three main objectives of this study were to (1) investigate low- and high-temperature-sensitive liposomes (LTSLs and HTSLs) containing the antimicrobial agent ciprofloxacin for temperature-mediated antibiotic release, (2) characterise in vitro ciprofloxacin release and stability and (3) study the efficacy of combining liposomal ciprofloxacin with AMF against Pseudomonas aeruginosa biofilms grown on metal washers. The release of ciprofloxacin from LTSL and HTSL was assessed in physiological buffers. Results demonstrated a lower transition temperature for both LTSL and HTSL formulations when incubated in serum as compared with PBS, with a more pronounced impact on the HTSLs. Upon combining AMF with temperature-sensitive liposomal ciprofloxacin, a 3 log reduction in CFU of Pseudomonas aeruginosa in biofilm was observed. Our initial studies suggest that AMF exposure on metal implants can trigger release of antibiotic from temperature sensitive liposomes for a potent bactericidal effect on biofilm.

Synthetic Macromolecular Antibiotic Platform for Inhalable Therapy against Aerosolized Intracellular Alveolar Infections

Lung-based intracellular bacterial infections remain one of the most challenging infectious disease settings. For example, the current standard for treating Franciscella tularensis pneumonia (tularemia) relies on administration of oral or intravenous antibiotics that poorly achieve and sustain pulmonary drug bioavailability. Inhalable antibiotic formulations are approved and in clinical development for upper respiratory infections, but sustained drug dosing from inhaled antibiotics against alveolar intracellular infections remains a current unmet need. To provide an extended therapy against alveolar intracellular infections, we have developed a macromolecular therapeutic platform that provides sustained local delivery of ciprofloxacin with controlled dosing profiles. Synthesized using RAFT polymerization, these macromolecular prodrugs characteristically have high drug loading (16-17 wt % drug), tunable hydrolysis kinetics mediated by drug linkage chemistry (slow-releasing alkyllic vs fast-releasing phenolic esters), and, in general, represent new fully synthetic nanotherapeutics with streamlined manufacturing profiles. In aerosolized and completely lethal F.t. novicida mouse challenge models, the fast-releasing ciprofloxacin macromolecular prodrug provided high cure efficiencies (75% survival rate under therapeutic treatment), and the importance of release kinetics was demonstrated by the inactivity of the similar but slow-releasing prodrug system. Pharmacokinetics and biodistribution studies further demonstrated that the efficacious fast-releasing prodrug retained drug dosing in the lung above the MIC over a 48 h period with corresponding C_max/MIC and AUC_0-24h/MIC ratios being greater than 10 and 125, respectively; the thresholds for optimal bactericidal efficacy. These findings identify the macromolecular prodrug platform as a potential therapeutic system to better treat alveolar intracellular infections such as F. tularensis, where positive patient outcomes require tailored antibiotic pharmacokinetic and treatment profiles.

Inhaled Liposomal Ciprofloxacin Protects against a Lethal Infection in a Murine Model of Pneumonic Plague

Inhalation of Yersinia pestis can lead to pneumonic plague, which without treatment is inevitably fatal. Two novel formulations of liposome-encapsulated ciprofloxacin, ‘ciprofloxacin for inhalation’ (CFI, Lipoquin^®) and ‘dual release ciprofloxacin for inhalation’ (DRCFI, Pulmaquin^®) containing CFI and ciprofloxacin solution, are in development. These were evaluated as potential therapies for infection with Y. pestis. In a murine model of pneumonic plague, human-like doses of aerosolized CFI, aerosolized DRCFI or intraperitoneal (i.p.) ciprofloxacin were administered at 24 h (representing prophylaxis) or 42 h (representing treatment) post-challenge. All three therapies provided a high level of protection when administered 24 h post-challenge. A single dose of CFI, but not DRCFI, significantly improved survival compared to a single dose of ciprofloxacin. Furthermore, single doses of CFI and DRCFI reduced bacterial burden in lungs and spleens to below the detectable limit at 60 h post-challenge. When therapy was delayed until 42 h post-challenge, a single dose of CFI or DRCFI offered minimal protection. However, single doses of CFI or DRCFI were able to significantly reduce the bacterial burden in the spleen compared to empty liposomes. A three-day treatment regimen of ciprofloxacin, CFI, or DRCFI resulted in high levels of protection (90–100% survival). This study suggests that CFI and DRCFI may be useful therapies for Y. pestis infection, both as prophylaxis and for the treatment of plague.

Tuning Ciprofloxacin Release Profiles from Liposomally Encapsulated Nanocrystalline Drug

Purpose

In order to attenuate the drug release rate, a single freeze-thaw step was previously shown to convert encapsulated drug into a single nanocrystal within each liposome vesicle. The goal of this study was to alter the nanocrystalline character, and thus the drug encapsulation state and release profile, by addition of surfactant prior to freeze-thaw.

Methods

A liposomal ciprofloxacin (CFI) formulation was modified by the addition of surfactant and frozen. After thawing, these formulations were characterized in terms of drug encapsulation by centrifugation-filtration, liposome structure by cryo-TEM imaging, vesicle size by dynamic light scattering, and in vitro release (IVR) performance.

Results

The addition of increasing levels of polysorbate 20 (0.05 to 0.4%) or Brij 30 (0.05 to 0.3%) to the CFI preparations followed by subsequent freeze-thaw, resulted in a greater proportion of vesicles without drug nanocrystals and reduced the extent of growth of the nanocrystals thus leading to modified release rates including an increase in the ratio of non-encapsulated to sustained release of drug.

Conclusions

This study provides another lever to achieve the desired release rate profile from a liposomal formulation by addition of surfactant and subsequent freeze-thaw, and thus may provide a personalized approach to treating patients.

Development of Liposomal Ciprofloxacin to Treat Lung Infections

Except for management of Pseudomonas aeruginosa (PA) in cystic fibrosis, there are no approved inhaled antibiotic treatments for any other diseases or for infections from other pathogenic microorganisms such as tuberculosis, non-tuberculous mycobacteria, fungal infections or potential inhaled biowarfare agents including Francisella tularensis, Yersinia pestis and Coxiella burnetii (which cause pneumonic tularemia, plague and Q fever, respectively). Delivery of an antibiotic formulation via the inhalation route has the potential to provide high concentrations at the site of infection with reduced systemic exposure to limit side effects. A liposomal formulation may improve tolerability, increase compliance by reducing the dosing frequency, and enhance penetration of biofilms and treatment of intracellular infections. Two liposomal ciprofloxacin formulations (Lipoquin^® and Pulmaquin^®) that are in development by Aradigm Corporation are described here.

Aerosol Performance and Stability of Liposomes Containing Ciprofloxacin Nanocrystals

Background: Previously we showed that the release properties of a liposomal ciprofloxacin (CFI) formulation could be attenuated by incorporation of drug nanocrystals within the vesicles. Rather than forming these drug nanocrystals during drug loading, they were created post manufacture simply by freezing and thawing the formulation. The addition of surfactant to CFI, either polysorbate 20 or Brij 30, provided an additional means to modify the release profile or incorporate an immediate-release or ‘burst’ component as well. The goal of this study was to develop a CFI formulation that retained its nanocrystalline morphology and attenuated release profile after delivery as an inhaled aerosol.

Methods: Preparations of 12.5 mg/mL CFI containing 90 mg/mL sucrose and 0.1% polysorbate 20 were formulated between pH 4.6 to 5.9, stored frozen, and thawed prior to use. These thawed formulations, before and after mesh nebulization, and after subsequent refrigerated storage for up to 6 weeks, were characterized in terms of liposome structure by cryogenic transmission electron microscopy (cryo-TEM) imaging, vesicle size by dynamic light scattering, pH, drug encapsulation by centrifugation-filtration, and in vitro release (IVR) performance.

Results: Within the narrower pH range of 4.9 to 5.3, these 12.5 mg/mL liposomal ciprofloxacin formulations containing 90 mg/mL sucrose and 0.1% polysorbate 20 retained their physicochemical stability for an additional 3 months refrigerated storage post freeze-thaw, were robust to mesh nebulization maintaining their vesicular form containing nanocrystalline drug and an associated slower release profile, and formed respirable aerosols with a mass median aerodynamic diameter (MMAD) of ∼3.9 μm and a geometric standard deviation (GSD) of ∼1.5.

Conclusions: This study demonstrates that an attenuated release liposomal ciprofloxacin formulation can be created through incorporation of drug nanocrystals in response to freeze-thaw, and the formulation retains its physicochemical properties after aerosolization by mesh nebulizer.