Fundamentals of pulmonary drug delivery

Formulation strategies, preparation methods, and devices for pulmonary delivery of biologics

Biological products, including vaccines, blood components, and recombinant therapeutic proteins, are derived from natural sources such as humans, animals, or microorganisms and are typically produced using advanced biotechnological methods. The success of biologics, particularly monoclonal antibodies, can be attributed to their favorable safety profiles and target specificity. However, their large molecular size presents significant challenges in drug delivery, particularly in overcoming biological barriers. Pulmonary delivery has emerged as a promising route for administering biologics, offering non-invasive delivery with rapid absorption, high systemic bioavailability, and avoidance of first-pass metabolism. This review first details the anatomy and physiological barriers of the respiratory tract and the associated challenges of pulmonary drug delivery (PDD). It further discusses innovations in PDD, the impact of particle size on drug deposition, and the use of secondary particles, such as nanoparticles, to enhance bioavailability and targeting. The review also explains various devices used for PDD, including dry powder inhalers (DPIs) and nebulizers, highlighting their advantages and limitations in delivering biologics. The role of excipients in improving the stability and performance of inhalation products is also addressed. Since dry powders are considered the suitable format for delivering biomolecules, particular emphasis is placed on the excipients used in DPI development. The final section of the article reviews and compares various dry powder manufacturing methods, clarifying their clinical relevance and potential for future applications in the field of inhalable drug formulation.

Pulmonary drug delivery devices and nanosystems as potential treatment strategies for acute respiratory distress syndrome (ARDS)

Despite advances in drug delivery technologies, treating acute respiratory distress syndrome (ARDS) is challenging due to pathophysiological barriers such as lung injury, oedema fluid build-up, and lung inflammation. Active pharmaceutical ingredients (API) can be delivered directly to the lung site of action with the use of aerosol-based drug delivery devices, and this circumvents the hepatic first-pass effect and improves the bioavailability of drugs. This review discusses the various challenges and barriers for pulmonary drug delivery, current interventions for delivery, considerations for effective drug delivery, and the use of nanoparticle drug delivery carriers as potential strategies for delivering therapeutics in ARDS. Nanosystems have the added benefit of entrapping drugs, increase pulmonary drug bioavailability, and using biocompatible and biodegradable excipients that can facilitate targeted and/or controlled delivery. These systems provide an alternative to existing conventional systems. An effective way to deliver drugs for the treatment of ARDS can be by using colloidal systems that are aerosolized or inhaled. Drug distribution to the deeper pulmonary tissues is necessary due to the significant endothelial cell destruction that is prevalent in ARDS. The particle size of nanoparticles (<0.5 μm) makes them ideal candidates for treating ARDS as they can reach the alveoli. A look into the various potential benefits and limitations of nanosystems used for other lung disorders is also considered to indicate how they may be useful for the potential treatment of ARDS.

Numerical and experimental evaluation of nasopharyngeal aerosol administration methods in children with adenoid hypertrophy

Administering aerosol drugs through the nasal pathway is a common early treatment for children with adenoid hypertrophy (AH). To enhance therapeutic efficacy, a deeper understanding of nasal drug delivery in the nasopharynx is essential. This study uses an integrated experimental, numerical modelling approach to investigate the delivery process of both the aerosol mask delivery system (MDS) and the bi-directional delivery system (BDS) in the pediatric nasal airway with AH. The combined effect of respiratory flow rates and particle size on delivery efficiency was systematically analyzed. The results showed that the nasopharyngeal peak deposition efficiency (DE) for BDS was approximately 2.25-3.73 times higher than that for MDS under low-flow, resting and high-flow respiratory conditions. Overall nasopharyngeal DEs for MDS were at a low level of below 16 %. For each respiratory flow rate, the BDS tended to achieve higher peak DEs (36.36 % vs 9.74 %, 37.80 % vs 14.01 %, 34.58 % vs 15.35 %) at smaller particle sizes (15 µm vs 17 µm, 10 µm vs 14 µm, 6 µm vs 9 µm). An optimal particle size exists for each respiratory flow rate, maximizing the drug delivery efficiency to the nasopharynx. The BDS is more effective in delivering drug aerosols to the nasal cavity and nasopharynx, which is crucial for early intervention in children with AH.

Deformation and breakup of compound droplets in airflow

HYPOTHESIS

Immiscible liquids are commonly used to achieve unique functions in many applications, where the breakup of compound droplets in airflow is an important process. Due to the existence of the liquid-liquid interface, compound droplets are expected to form different deformation and breakup morphologies compared with single-component droplets.

EXPERIMENTS

We investigate experimentally the deformation and breakup of compound droplets in airflow. The deformation characteristics of compound droplets are quantitatively analyzed and compared with single-component droplets. Theoretical models are proposed to analyze the transition between breakup morphologies.

FINDINGS

The breakup modes of compound droplets are classified into shell retraction, shell breakup, and core-shell breakup based on the location where the breakup occurs. The comparison with single-component droplets reveals that the compound droplet is stretched more in the flow direction and expands less in the cross-flow direction, and these differences occur when the core of the compound droplet protrudes into the airflow. The transition conditions between different breakup modes are obtained theoretically. In addition, the eccentricity of the compound droplet can lead to the formation of the thick ligament or the two stamens in the droplet middle.

Zwitterionic Inhaler with Synergistic Therapeutics for Reprogramming of M2 Macrophage to Pro-Inflammatory Phenotype

Myriad lung diseases are life threatening and macrophages play a key role in both physiological and pathological processes. Macrophages have each pro-/anti-inflammatory phenotype, and each lung disease can be aggravated by over-polarized macrophage. Therefore, development of a method capable of mediating the macrophage phenotype is one of the solutions for lung disease treatment. For mediating the phenotype of macrophages, the pulmonary delivery system (PDS) is widely used due to its advantages, such as high efficiency and accessibility of the lungs. However, it has a low drug delivery efficiency ironically because of the perfect lung defense system consisting of the mucus layer and airway macrophages. In this study, zwitterion-functionalized poly(lactide-co-glycolide) (PLGA) inhalable microparticles (ZwPG) are synthesized to increase the efficiency of the PDS. The thin layer of zwitterions formed on PLGA surface has high nebulizing stability and show high anti-mucus adhesion and evasion of macrophages. As a reprogramming agent for macrophages, ZwPG containing dexamethasone (Dex) and pirfenidone (Pir) are treated to over-polarized M2 macrophages. As a result, a synergistic effect of Dex/Pir induces reprogramming of M2 macrophage to pro-inflammatory phenotypes.

Drug combinations for inhalation: Current products and future development addressing disease control and patient compliance

Pulmonary delivery is an alternative route of administration with numerous advantages over conventional routes of administration. It provides low enzymatic exposure, fewer systemic side effects, no first-pass metabolism, and concentrated drug amounts at the site of the disease, making it an ideal route for the treatment of pulmonary diseases. Owing to the thin alveolar-capillary barrier, and large surface area that facilitates rapid absorption to the bloodstream in the lung, systemic delivery can be achieved as well. Administration of multiple drugs at one time became urgent to control chronic pulmonary diseases such as asthma and COPD, thus, development of drug combinations was proposed. Administration of medications with variable dosages from different inhalers leads to overburdening the patient and may cause low therapeutic intervention. Therefore, products that contain combined drugs to be delivered via a single inhaler have been developed to improve patient compliance, reduce different dose regimens, achieve higher disease control, and boost therapeutic effectiveness in some cases. This comprehensive review aimed to highlight the growth of drug combinations by inhalation over time, obstacles and challenges, and the possible progress to broaden the current options or to cover new indications in the future. Moreover, various pharmaceutical technologies in terms of formulation and device in correlation with inhaled combinations were discussed in this review. Hence, inhaled combination therapy is driven by the need to maintain and improve the quality of life for patients with chronic respiratory diseases; promoting drug combinations by inhalation to a higher level is a necessity.

Noninvasive and Microinvasive Nanoscale Drug Delivery Platforms for Hard Tissue Engineering

Bone tissue plays a crucial role in protecting internal organs and providing structural support and locomotion of the body. Treatment of hard tissue defects and medical conditions due to physical injuries, genetic disorders, aging, metabolic syndromes, and infections is more often a complex and drawn out process. Presently, dealing with hard-tissue-based clinical problems is still mostly conducted via surgical interventions. However, advances in nanotechnology over the last decades have led to shifting trends in clinical practice toward noninvasive and microinvasive methods. In this review article, recent advances in the development of nanoscale platforms for bone tissue engineering have been reviewed and critically discussed to provide a comprehensive understanding of the advantages and disadvantages of noninvasive and microinvasive methods for treating medical conditions related to hard tissue regeneration and repair.

Inhaled drug delivery for the targeted treatment of asthma

Asthma is a chronic lung disease affecting millions worldwide. While classically acknowledged to result from allergen-driven type 2 inflammatory responses leading to IgE and cytokine production and the influx of immune cells such as mast cells and eosinophils, the wide range in asthmatic pathobiological subtypes lead to highly variable responses to anti-inflammatory therapies. Thus, there is a need to develop patient-specific therapies capable of addressing the full spectrum of asthmatic lung disease. Moreover, delivery of targeted treatments for asthma directly to the lung may help to maximize therapeutic benefit, but challenges remain in design of effective formulations for the inhaled route. In this review, we discuss the current understanding of asthmatic disease progression as well as genetic and epigenetic disease modifiers associated with asthma severity and exacerbation of disease. We also overview the limitations of clinically available treatments for asthma and discuss pre-clinical models of asthma used to evaluate new therapies. Based on the shortcomings of existing treatments, we highlight recent advances and new approaches to treat asthma via inhalation for monoclonal antibody delivery, mucolytic therapy to target airway mucus hypersecretion and gene therapies to address underlying drivers of disease. Finally, we conclude with discussion on the prospects for an inhaled vaccine to prevent asthma.

Recent Advances in Inhaled Nanoformulations of Vaccines and Therapeutics Targeting Respiratory Viral Infections

With the rapid outbreak of respiratory viral infections, various biological (e.g. vaccines, peptides, recombinant proteins, antibodies and genes) and antiviral agents (e.g. ribavirin, palivizumab and valaciclovir) have been successfully developed for the treatment of respiratory virus infections such as influenza, respiratory syncytial virus and SARS-CoV-2 infections. These therapeutics are conventionally delivered via oral, intramuscular or injection route and are associated with several adverse events due to systemic toxicity. The inherent in vivo instability of biological therapeutics may hinder them from being administered without proper formulations. Therefore, we have witnessed a boom in nanotechnology coupled with a needle-free administration approach such as the inhalation route for the delivery of complex therapeutics to treat respiratory infections. This review discussed the recent advances in the inhalation strategies of nanoformulations that target virus respiratory infections.

A Systematic Review of Clinical Pharmacokinetics of Inhaled Antiviral

Background and Objectives: The study of clinical pharmacokinetics of inhaled antivirals is particularly important as it helps one to understand the therapeutic efficacy of these drugs and how best to use them in the treatment of respiratory viral infections such as influenza and the current COVID-19 pandemic. The article presents a systematic review of the available pharmacokinetic data of inhaled antivirals in humans, which could be beneficial for clinicians in adjusting doses for diseased populations. Materials and Methods: This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. A comprehensive literature search was conducted using multiple databases, and studies were screened by two independent reviewers to assess their eligibility. Data were extracted from the eligible studies and assessed for quality using appropriate tools. Results: This systematic review evaluated the pharmacokinetic parameters of inhaled antiviral drugs. The review analyzed 17 studies, which included Zanamivir, Laninamivir, and Ribavirin with 901 participants, and found that the non-compartmental approach was used in most studies for the pharmacokinetic analysis. The outcomes of most studies were to assess clinical pharmacokinetic parameters such as the Cmax, AUC, and t1/2 of inhaled antivirals. Conclusions: Overall, the studies found that the inhaled antiviral drugs were well tolerated and exhibited favorable pharmacokinetic profiles. The review provides valuable information on the use of these drugs for the treatment of influenza and other viral respiratory infections.

An evolving perspective on novel modified release drug delivery systems for inhalational therapy

INTRODUCTION

Drugs delivered via the lungs are predominantly used to treat various respiratory disorders, including asthma, chronic obstructive pulmonary diseases, respiratory tract infections and lung cancers, and pulmonary vascular diseases such as pulmonary hypertension. To treat respiratory diseases, targeted, modified or controlled release inhalation formulations are desirable for improved patient compliance and superior therapeutic outcome.

AREAS COVERED

This review summarizes the important factors that have an impact on the inhalable modified release formulation approaches with a focus toward various formulation strategies, including dissolution rate-controlled systems, drug complexes, site-specific delivery, drug-polymer conjugates, and drug-polymer matrix systems, lipid matrix particles, nanosystems, and formulations that can bypass clearance via mucociliary system and alveolar macrophages.

EXPERT OPINION

Inhaled modified release formulations can potentially reduce dosing frequency by extending drug's residence time in the lungs. However, inhalable modified or controlled release drug delivery systems remain unexplored and underdeveloped from the commercialization perspective. This review paper addresses the current state-of-the-art of inhaled controlled release formulations, elaborates on the avenues for developing newer technologies for formulating various drugs with tailored release profiles after inhalational delivery and explains the challenges associated with translational feasibility of modified release inhalable formulations.

Opportunistic etiological agents causing lung infections: emerging need to transform lung-targeted delivery

Lung diseases continue to draw considerable attention from biomedical and public health care agencies. The lung with the largest epithelial surface area is continuously exposed to the external environment during exchanging gas. Therefore, the chances of respiratory disorders and lung infections are overgrowing. This review has covered promising and opportunistic etiologic agents responsible for lung infections. These pathogens infect the lungs either directly or indirectly. However, it is difficult to intervene in lung diseases using available oral or parenteral antimicrobial formulations. Many pieces of research have been done in the last two decades to improve inhalable antimicrobial formulations. However, very few have been approved for human use. This review article discusses the approved inhalable antimicrobial agents (AMAs) and identifies why pulmonary delivery is explored. Additionally, the basic anatomy of the respiratory system linked with barriers to AMA delivery has been discussed here. This review opens several new scopes for researchers to work on pulmonary medicines for specific diseases and bring more respiratory medication to market.

Penetration and translocation of functional inorganic nanomaterials into biological barriers

With excellent physicochemical properties, inorganic nanomaterials (INMs) have exhibited a series of attractive applications in biomedical fields. Biological barriers prevent successful delivery of nanomedicine in living systems that limits the development of nanomedicine especially for sufficient delivery of drugs and effective therapy. Numerous researches have focused on overcoming these biological barriers and homogeneity of organisms to enhance therapeutic efficacy, however, most of these strategies fail to resolve these challenges. In this review, we present the latest progress about how INMs interact with biological barriers and penetrate these barriers. We also summarize that both native structure and components of biological barriers and physicochemical properties of INMs contributed to the penetration capacity. Knowledge about the relationship between INMs structure and penetration capacity will guide the design and application of functional and efficient nanomedicine in the future.

Mechanisms and challenges of nanocarriers as non-viral vectors of therapeutic genes for enhanced pulmonary delivery

With the rapid development of biopharmaceuticals and the outbreak of COVID-19, the world has ushered in a frenzy to develop gene therapy. Therefore, therapeutic genes have received enormous attention. However, due to the extreme instability and low intracellular gene expression of naked genes, specific vectors are required. Viral vectors are widely used attributed to their high transfection efficiency. However, due to the safety concerns of viral vectors, nanotechnology-based non-viral vectors have attracted extensive investigation. Still, issues of low transfection efficiency and poor tissue targeting of non-viral vectors need to be addressed. Especially, pulmonary gene delivery has obvious advantages for the treatment of inherited lung diseases, lung cancer, and viral pneumonia, which can not only enhance lung targeting and but also reduce enzymatic degradation. For systemic diseases therapy, pulmonary gene delivery can enhance vaccine efficacy via inducing not only cellular, humoral immunity but also mucosal immunity. This review provides a comprehensive overview of nanocarriers as non-viral vectors of therapeutic genes for enhanced pulmonary delivery. First of all, the characteristics and therapeutic mechanism of DNA, mRNA, and siRNA are provided. Thereafter, the advantages and challenges of pulmonary gene delivery in exerting local and systemic effects are discussed. Then, the inhalation dosage forms for nanoparticle-based drug delivery systems are introduced. Moreover, a series of materials used as nanocarriers for pulmonary gene delivery are presented, and the endosomal escape mechanisms of nanocarriers based on different materials are explored. The application of various non-viral vectors for pulmonary gene delivery are summarized in detail, with the perspectives of nano-vectors for pulmonary gene delivery.

Therapeutic Use of an Inhaled Drug Delivery in Pulmonary Hypertension: A Review

Pulmonary arterial hypertension (PAH) is a serious condition in which there is increased blood pressure in arteries of the lungs (pulmonary arteries). The therapies or drugs for PAH have expanded with the revelation of three key pathological processes - encompassing prostacyclin, nitric oxide (NO), and endothelin pathways. An outlook for patients suffering from PAH is still mediocre amidst recent advancements. The evolution of pre-clinical and clinical research on PAH has facilitated the identification of several new targeted therapies for the disease. In this article, we examine recent data on new pulmonary hypertension physiological pathways, primarily concentrating on administering drugs through the inhalation route and their effects. Although they have been given clinical use approval, medications based on these routes are presently being studied in clinical or pre-clinical settings. To confirm these innovative medicines' therapeutic efficacy and safety, extensive clinical trials are needed.

Pulmonary drug delivery applications of natural polysaccharide polymer derived nano/micro-carrier systems: A review

Respiratory distress syndrome and pneumothorax are the foremost causes of death as a result of the changing lifestyle and increasing air pollution. Numerous approaches have been studied for the pulmonary delivery of drugs, proteins as well as peptides using meso/nanoparticles, nanocrystals, and liposomes. These nano/microcarrier systems (NMCs) loaded with drug provide better systemic as well as local action. Furthermore, natural polysaccharide-based polymers such as chitosan (CS), alginate (AG), hyaluronic acid, dextran, and cellulose are highly used for the preparation of nanoparticles and delivery of the drug into the pulmonary tract due to their advantageous properties such as low toxicity, high hydrophobicity, supplementary mucociliary clearance, mucoadhesivity, and biological efficacy. These properties ease the delivery of drugs onto the targeted site. Herein, recent advances in the natural polymer-derived NMCs have been reviewed for their transport and mechanism of action into the bronchiolar region as well as the respiratory region. Various physicochemical properties such as surface charge, size of nanocarrier system, surface modifications, and toxicological effects of these nanocarriers in vitro and in vivo are elucidated as well. Furthermore, challenges faced for the preparation of a model NMCs for pulmonary drug delivery are also discoursed.

Post-COVID Syndrome: The Research Progress in the Treatment of Pulmonary sequelae after COVID-19 Infection

Post-COVID syndrome or long COVID is defined as the persistence of symptoms after confirmed SARS-CoV-2 infection, the pathogen responsible for coronavirus disease. The content herein presented reviews the reported long-term consequences and aftereffects of COVID-19 infection and the potential strategies to adopt for their management. Recent studies have shown that severe forms of COVID-19 can progress into acute respiratory distress syndrome (ARDS), a predisposing factor of pulmonary fibrosis that can irreversibly compromise respiratory function. Considering that the most serious complications are observed in the airways, the inhalation delivery of drugs directly to the lungs should be preferred, since it allows to lower the dose and systemic side effects. Although further studies are needed to optimize these techniques, recent studies have also shown the importance of in vitro models to recreate the SARS-CoV-2 infection and study its sequelae. The information reported suggests the necessity to develop new inhalation therapies in order to improve the quality of life of patients who suffer from this condition.

Radiolabeling Method for Lyophilizate for Dry Powder Inhalation Formulations

Human lung deposition data is non-mandatory for drug approval but very useful for the development of orally inhaled drug products. Lung deposition of inhaled drugs can be quantified by radionuclide imaging, for which one of the first considerations is the method used to radiolabel formulations. In this study, we report the development of a radiolabeling method for lyophilizate for dry powder inhalation (LDPI) formulations. TechneCoatTM is one method that can radiolabel drug particles without using solvents. In this method, particles are radiolabeled with a dispersion of 99mTc-labeled nanoparticles called TechnegasTM. Because a LDPI formulation is not comprised of particles but is a lyophilized cake aerosolized by air impact, the TechneCoat method cannot be used for the radiolabeling of LDPI formulations. We therefore modified the TechneCoat apparatus so that LDPI formulations were not aerosolized by the Technegas flow. Radiolabeling using a modified TechneCoat apparatus was validated with model LDPI formulations of interferon alpha (IFN). IFN of 99mTc-unlabeled, IFN of 99mTc-labeled, and 99mTc of 99mTc-labeled LDPI formulations showed similar behavior, and differences from IFN of 99mTc-unlabeled LDPI formulations were within ±15% in aerodynamic particle size distribution measurement. Our radiolabeling method for LDPI formulations may be useful for the quantification of drug deposition in human lungs.

Taking leads out of nature, can nano deliver us from COVID-like pandemics?

The COVID-19 crisis has alerted the research community to re-purpose scientific tools that can effectively manage emergency pandemic situations. Researchers were never so desperate to discover a 'magic bullet' that has significant clinical benefits with minimal or no side effects. At the beginning of the pandemic, due to restricted access to traditional laboratory techniques, many research groups delved into computational screening of thousands of lead molecules that could inhibit SARS-CoV-2 at one or more stages of its infectious cycle. Several in silico studies on natural derivatives point out their potency against SARS-CoV-2 proteins. However, theoretical predictions and existing knowledge on related molecules reflect their poor oral bioavailability due to biotransformation in the gut and liver. Nanotechnology has evolved into a key field for precise and controlled delivery of various drugs that lack aqueous solubility, have low oral bioavailability and possess pronounced toxicity in their native form. In this review, we discuss various nanoformulations of natural products with favorable ADME properties, and also briefly explore nano-drug delivery to lungs, the primary site of SARS-CoV-2 infection. Natural products are also envisioned to augment nanotechnology-based 1) personnel protective equipment for ex vivo viral inactivation and 2) wearable sensors that perform rapid and non-invasive analysis of volatile organic compounds in exhaled breath of the infected person after therapeutic food consumption.

The future of dry powder inhaled therapy: Promising or Discouraging for systemic disorders?

Dry powder inhalation therapy has been shown to be an effective method for treating respiratory diseases like asthma, Chronic Obstructive Pulmonary Diseases and Cystic Fibrosis. It has also been widely accepted and used in clinical practices. Such success has led to great interest in inhaled therapy on treating systemic diseases in the past two decades. The current coronavirus (COVID-19) pandemic also has increased such interest and is triggering more potential applications of dry powder inhalation therapy in vaccines and antivirus drugs. Would the inhaled dry powder therapy on systemic disorders be as encouraging as expected? This paper reviews the marketed and in-development dry powder inhaler (DPI) products on the treatment of systemic diseases, their status in clinical trials, as well as the potential for COVID-19 treatment. The advancements and unmet problems on DPI systems are also summarized. With countless attempts behind and more challenges ahead, it is believed that the dry powder inhaled therapy for the treatment of systemic disorders still holds great potential and promise.

Nebulizer systems: a new frontier for therapeutics and targeted delivery

Drug delivery via the pulmonary route is a cornerstone in the pharmaceutical sector as an alternative to oral and parenteral administration. Nebulizer inhalation treatment offers multiple drug administration, easily employed with tidal breathing, suitable for children and elderly, can be adapted for severe patients and visible spray ensures patient satisfaction. This review discusses the operational and mechanical characteristics of nebulizer delivery devices in terms of aerosol production processes, their usage, benefits and drawbacks that are currently shaping the contemporary landscape of inhaled drug delivery. With the advent of particle engineering, novel inhaled nanosystems can be successfully developed to increase lung deposition and decrease pulmonary clearance. The above-mentioned advances might pave the path for treating a life-threatening disorder like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which is also discussed in the current state of the art.

Challenges and solutions in polymer drug delivery for bacterial biofilm treatment: A tissue-by-tissue account

To tackle the emerging antibiotic resistance crisis, novel antimicrobial approaches are urgently needed. Bacterial communities (biofilms) are a particular concern in this context. Biofilms are responsible for most human infections and are inherently less susceptible to antibiotic treatments. Biofilms have been linked with several challenging chronic diseases, including implant-associated osteomyelitis and chronic wounds. The specific local environments present in the infected tissues further contribute to the rise in antibiotic resistance by limiting the efficacy of systemic antibiotic therapies and reducing drug concentrations at the infection site, which can lead to reoccurring infections. To overcome the shortcomings of systemic drug delivery, encapsulation within polymeric carriers has been shown to enhance antimicrobial efficacy, permeation and retention at the infection site. In this Review, we present an overview of current strategies for antimicrobial encapsulation within polymeric carriers, comparing challenges and solutions on a tissue-by-tissue basis. We compare challenges and proposed drug delivery solutions from the perspective of the local environments for biofilms found in oral, wound, gastric, urinary tract, bone, pulmonary, vaginal, ocular and middle/inner ear tissues. We will also discuss future challenges and barriers to clinical translation for these therapeutics. The following Review demonstrates there is a significant imbalance between the research focus being placed on different tissue types, with some targets (oral and wound biofims) being extensively more studied than others (vaginal and otitis media biofilms and endocarditis). Furthermore, the importance of the local tissue environment when selecting target therapies is demonstrated, with some materials being optimal choices for certain sites of bacterial infection, while having limited applicability in others.

Drug Repurposing in the COVID-19 Era: Insights from Case Studies Showing Pharmaceutical Peculiarities

COVID-19 may lead to severe respiratory distress syndrome and high risk of death in some patients. So far (January 2021), only the antiviral remdesivir has been approved, although no significant benefits in terms of mortality and clinical improvement were recently reported. In a setting where effective and safe treatments for COVID-19 are urgently needed, drug repurposing may take advantage of the fact that the safety profile of an agent is already well known and allows rapid investigation of the efficacy of potential treatments, at lower costs and with reduced risk of failure. Furthermore, novel pharmaceutical formulations of older agents (e.g., aerosolized administration of chloroquine/hydroxychloroquine, remdesivir, heparin, pirfenidone) have been tested in order to increase pulmonary delivery and/or antiviral effects of potentially active drugs, thus overcoming pharmacokinetic issues. In our review, we will highlight the importance of the drug repurposing strategy in the context of COVID-19, including regulatory and ethical aspects, with a specific focus on novel pharmaceutical formulations and routes of administration.

Pulmonary route of administration is instrumental in developing therapeutic interventions against respiratory diseases

Pulmonary route of drug delivery has drawn significant attention due to the limitations associated with conventional routes and available treatment options. Drugs administered through pulmonary route has been an important research area that focuses on to developing effective therapeutic interventions for asthma, chronic obstructive pulmonary disease, tuberculosis, lung cancer etc. The intravenous route has been a natural route of delivery of proteins and peptides but associated with several issues including high cost, needle-phobia, pain, sterility issues etc. These issues might be addressed by the pulmonary administration of macromolecules to achieving an effective delivery and efficacious therapeutic impact. Efforts have been made to develop novel drug delivery systems (NDDS) such as nanoparticles, microparticles, liposomes and their engineered versions, polymerosomes, micelles etc to achieving targeted and sustained delivery of drug(s) through pulmonary route. Further, novel approaches such as polymer-drug conjugates, mucoadhesive particles and mucus penetrating particles have attracted significant attention due to their unique features for an effective delivery of drugs. Also, use of semi flourinated alkanes is in use for improvising the pulmonary delivery of lipophilic drugs. Present review focuses on to unravel the mechanism of pulmonary absorption of drugs for major pulmonary diseases. It summarizes the development of interventional approaches using various particulate and vesicular drug delivery systems. In essence, the orchestrated attempt presents an inflammatory narrative on the advancements in the field of pulmonary drug delivery.

Pulmonary Delivery of Biological Drugs

In the last decade, biological drugs have rapidly proliferated and have now become an important therapeutic modality. This is because of their high potency, high specificity and desirable safety profile. The majority of biological drugs are peptide- and protein-based therapeutics with poor oral bioavailability. They are normally administered by parenteral injection (with a very few exceptions). Pulmonary delivery is an attractive non-invasive alternative route of administration for local and systemic delivery of biologics with immense potential to treat various diseases, including diabetes, cystic fibrosis, respiratory viral infection and asthma, etc. The massive surface area and extensive vascularisation in the lungs enable rapid absorption and fast onset of action. Despite the benefits of pulmonary delivery, development of inhalable biological drug is a challenging task. There are various anatomical, physiological and immunological barriers that affect the therapeutic efficacy of inhaled formulations. This review assesses the characteristics of biological drugs and the barriers to pulmonary drug delivery. The main challenges in the formulation and inhalation devices are discussed, together with the possible strategies that can be applied to address these challenges. Current clinical developments in inhaled biological drugs for both local and systemic applications are also discussed to provide an insight for further research.

Respiratory Tract: Structure and Attractions for Drug Delivery Using Dry Powder Inhalers

Respiratory tract is one of the oldest routes for drug delivery. It can be used for local and systemic drug deliveries. Inhalation therapy has several advantages over oral. It delivers the drug efficiently to the lung with minimal systemic exposure, thus avoiding systemic side effects common with oral route. In this review, different types of inhaler devices are illustrated like metered dose inhalers (MDIs), dry powder inhalers (DPIs), nebulizers, and the new soft mist inhalers (SMIs). Since dry powder is more stable than when in liquid form, we will discuss in detail DPIs highlighting different techniques utilized in preparation of dry powders with or without carrier to improve flowability and drug delivery to deep lungs. Types of DPIs are briefly discussed with examples from the market. Several mechanisms for particle deposition are mentioned with factors governing the process. Pharmacokinetic profile of the inhaled particles is detailed starting from the dissolution, followed by the rapid absorption and ending with systemic clearance. New technologies like 3D printing in pulmonary field are also highlighted.

Inhaled nanoparticles-An updated review

We are providing an update to our previously published review paper on inhaled nanoparticles, thus updating with the most recent reports in the literature. The field of nanotechnology may hold the promise of significant improvements in the health and well-being of patients, as well as in manufacturing technologies. The knowledge of the impact of nanomaterials on public health is limited so far. This paper reviews the unique size-controlled properties of nanomaterials, their disposition in the body after inhalation, and the factors influencing the fate of inhaled nanomaterials. The physiology of the lungs makes it an ideal target organ for non-invasive local and systemic drug delivery, especially for protein and poorly water-soluble drugs that have low oral bioavailability via oral administration. More recently, inhaled nanoparticles have been reported to improve therapeutic efficacies and decrease undesirable side effects via pulmonary delivery. The potential application of pulmonary drug delivery of nanoparticles to the lungs, specifically in context of published results reported on nanomaterials in environmental epidemiology and toxicology is reviewed in this paper. This article presents updated delivery systems, process technologies, and potential of inhaled nanoparticles for local and systemic therapies administered to the lungs. The authors acknowledge the contributions of Wei Yang in our 2008 paper published in this journal.

Scope and limitations on aerosol drug delivery for the treatment of infectious respiratory diseases

The rise of antimicrobial resistance has created an urgent need for the development of new methods for antibiotics delivery to patients with pulmonary infections in order to mainly increase the effectiveness of the drugs administration, to minimize the risk of emergence of resistant strains, and to prevent patients reinfection. Since bacterial resistance is often related to antibiotic concentration, their pulmonary administration could eradicate strains resistant to the same drug at the concentration achieved through the systemic circulation. Pulmonary administration offers several advantages; it directly targets the site of the infection which allows the inhaled dose of the drug to be reduced compared to that administered orally or parenterally while keeping the same local effect. The review article is made with an objective to compile information about various existing modern technologies developed to provide greater patient compliance and reduce the undesirable side effect of the drugs. In conclusion, aerosol antibiotic delivery appears as one of the best technologies for the treatment of pulmonary infectious diseases and able to limit the systemic adverse effects related to the high drug dose and to make life easier for the patients.

Engineering of Nebulized Metal-Phenolic Capsules for Controlled Pulmonary Deposition

Particle-based pulmonary delivery has great potential for delivering inhalable therapeutics for local or systemic applications. The design of particles with enhanced aerodynamic properties can improve lung distribution and deposition, and hence the efficacy of encapsulated inhaled drugs. This study describes the nanoengineering and nebulization of metal-phenolic capsules as pulmonary carriers of small molecule drugs and macromolecular drugs in lung cell lines, a human lung model, and mice. Tuning the aerodynamic diameter by increasing the capsule shell thickness (from ≈100 to 200 nm in increments of ≈50 nm) through repeated film deposition on a sacrificial template allows precise control of capsule deposition in a human lung model, corresponding to a shift from the alveolar region to the bronchi as aerodynamic diameter increases. The capsules are biocompatible and biodegradable, as assessed following intratracheal administration in mice, showing >85% of the capsules in the lung after 20 h, but <4% remaining after 30 days without causing lung inflammation or toxicity. Single-cell analysis from lung digests using mass cytometry shows association primarily with alveolar macrophages, with >90% of capsules remaining nonassociated with cells. The amenability to nebulization, capacity for loading, tunable aerodynamic properties, high biocompatibility, and biodegradability make these capsules attractive for controlled pulmonary delivery.

Newer approaches and novel drugs for inhalational therapy for pulmonary arterial hypertension

Introduction: Pulmonary arterial hypertension (PAH) is a progressive disease characterized by remodeling of small pulmonary arteries leading to increased pulmonary arterial pressure. Existing treatments acts to normalize vascular tone via three signaling pathways: the prostacyclin, the endothelin-1, and the nitric oxide. Although over the past 20 years, there has been considerable progress in terms of treatments for PAH, the disease still remains incurable with a disappointing prognosis.Areas covered: This review summarizes the pathophysiology of PAH, the advantages and disadvantages of the inhalation route, and assess the relative advantages various inhaled therapies for PAH. The recent studies concerning the development of controlled-release drug delivery systems loaded with available anti-PAH drugs have also been summarized.Expert opinion: The main obstacles of current pharmacotherapies of PAH are their short half-life, stability, and formulations, resulting in reducing the efficacy and increasing systemic side effects and unknown pathogenesis of PAH. The pulmonary route has been proposed for delivering anti-PAH drugs to overcome the shortcomings. However, the application of approved inhaled anti-PAH drugs is limited. Inhalational delivery of controlled-release nanoformulations can overcome these restrictions. Extensive studies are required to develop safe and effective drug delivery systems for PAH patients.

Novel drug delivery systems and significance in respiratory diseases

Pulmonary drug delivery offers targeted therapy for the treatment of respiratory diseases such as asthma, lung cancer, and chronic obstructive pulmonary diseases. However, this route poses challenges like deposition mechanism, drug instability, and rapid clearance mechanism. Other factors like the type of inhaler device, patient compatibility, consistent delivery by device, and inhaler technique also affect the performance of pulmonary delivery systems. Thus, to overcome these issues, pulmonary delivery systems utilizing particle-based approaches (nano/microparticles) have emerged in the last two decades. This chapter provides insight into various mechanisms of pulmonary drug administration, the ideal requirements of a pulmonary system, and the general devices used for pulmonary delivery. An overview of new pulmonary delivery systems and their relevance in the treatment of respiratory diseases is provided. In the end, novel pulmonary technologies that have been patented and cleared clinical trials have been highlighted along with the advances in the inhaler device.

Identification of Factors of Importance for Spray Drying of Small Interfering RNA-Loaded Lipidoid-Polymer Hybrid Nanoparticles for Inhalation

BACKGROUND

With the recent approval of the first small interfering RNA (siRNA) therapeutic formulated as nanoparticles, there is increased incentive for establishing the factors of importance for the design of stable solid dosage forms of such complex nanomedicines.

METHODS

The aims of this study were: (i) to identify factors of importance for the design of spray-dried siRNA-loaded lipidoid-poly(DL-lactic-co-glycolic acid) hybrid nanoparticles (LPNs), and (ii) to evaluate their influence on the resulting powders by using a quality-by-design approach. Critical formulation and process parameters were linked to critical quality attributes (CQAs) using design of experiments, and an optimal operating space (OOS) was identified.

RESULTS

A series of CQAs were identified based on the quality target product profile. The loading (ratio of LPNs to the total solid content) and the feedstock concentration were determined as critical parameters, which were optimized systematically. Mannitol was chosen as stabilizing excipient due to the low water content of the resulting powders. The loading negatively affected the colloidal stability of the LPNs, whereas feedstock concentration correlated positively with the powder particle size. The optimal mannitol-based solid formulation, defined from the OOS, displayed a loading of 5% (w/w), mass median aerodynamic diameter of 3.3 ± 0.2 μm, yield of 60.6 ± 6.6%, and a size ratio of 1.15 ± 0.03. Dispersed micro-embedded LPNs had preserved physicochemical characteristics as well as in vitro siRNA release profile and gene silencing, as compared to non-spray-dried LPNs.

CONCLUSION

The optimal solid dosage forms represent robust formulations suitable for higher scale-up manufacturing.

Formulation and evaluation of carrier-free dry powder inhaler containing sildenafil

Pulmonary delivery of sildenafil for the treatment of pulmonary arterial hypertension could overcome the limitations of intravenous and oral administration routes, such as poor patient compliance and systemic side effects. In this study, a carrier-free dry powder inhaler (DPI) formulation was developed, using spray drying technique and L-leucine as a dispersibility enhancer. Sildenafil citrate salt and sildenafil free base were evaluated for drug transport using a Calu-3 cell model, and their suitability for DPI production by spray drying was tested. Characteristics of the resultant carrier-free DPI powders were examined, namely crystallinity, morphology, size distribution, density, zeta potential, and aerodynamic performance. A Box-Behnken design was adopted to optimize the formulation and process conditions, including leucine amount, fraction of methanol in spraying solvent, and inlet temperature. While both sildenafil forms exhibited sufficient permeability for lung absorption, only sildenafil base resulted in DPI powders which were stable for 6 months. The introduction of leucine into the formulations effectively enhanced aerodynamic performance of the powders and particles with favorable size, shape, and density were produced. The optimal DPI formulation determined from experimental design possesses excellent aerodynamic performance with 89.39% emitted dose and 80.08% fine particle fraction, indicating the possibility of incorporating sildenafil into carrier-free DPIs for pulmonary delivery.

Targeted Gene Delivery through the Respiratory System: Rationale for Intratracheal Gene Transfer

Advances in DNA- and RNA-based technologies have made gene therapy suitable for many lung diseases, especially those that are hereditary. The main objective of gene therapy is to deliver an adequate amount of gene construct to the intended target cell, achieve stable transduction in target cells, and to produce a clinically therapeutic effect. This review focuses on the cellular organization in the normal lung and how gene therapy targets the specific cell types that are affected by pulmonary disorders caused by genetic mutations. Furthermore, it examines the pulmonary barriers that can compromise the absorption and transduction of viral vectors and genetic agents by the lung. Finally, it discusses the advantages and limitations of direct intra-tracheal gene delivery with different viral vectors in small and large animal models and in clinical trials.

A Comprehensive Map of FDA-Approved Pharmaceutical Products

With the increasing research and development (R&D) difficulty of new molecular entities (NMEs), novel drug delivery systems (DDSs) are attracting widespread attention. This review investigated the current distribution of Food and Drug Administration (FDA)-approved pharmaceutical products and evaluated the technical barrier for the entry of generic drugs and highlighted the success and failure of advanced drug delivery systems. According to the ratio of generic to new drugs and the four-quadrant classification scheme for evaluating the commercialization potential of DDSs, the results showed that the traditional dosage forms (e.g., conventional tablets, capsules and injections) with a lower technology barrier were easier to reproduce, while advanced drug delivery systems (e.g., inhalations and nanomedicines) with highly technical barriers had less competition and greater market potential. Our study provides a comprehensive insight into FDA-approved products and deep analysis of the technical barriers for advanced drug delivery systems. In the future, the R&D of new molecular entities may combine advanced delivery technologies to make drug candidates into more therapeutically effective formulations.

Inhaled nanomaterials and the respiratory microbiome: clinical, immunological and toxicological perspectives

Our development and usage of engineered nanomaterials has grown exponentially despite concerns about their unfavourable cardiorespiratory consequence, one that parallels ambient ultrafine particle exposure from vehicle emissions. Most research in the field has so far focused on airway inflammation in response to nanoparticle inhalation, however, little is known about nanoparticle-microbiome interaction in the human airway and the environment. Emerging evidence illustrates that the airway, even in its healthy state, is not sterile. The resident human airway microbiome is further altered in chronic inflammatory respiratory disease however little is known about the impact of nanoparticle inhalation on this airway microbiome. The composition of the airway microbiome, which is involved in the development and progression of respiratory disease is dynamic, adding further complexity to understanding microbiota-host interaction in the lung, particularly in the context of nanoparticle exposure. This article reviews the size-dependent properties of nanomaterials, their body deposition after inhalation and factors that influence their fate. We evaluate what is currently known about nanoparticle-microbiome interactions in the human airway and summarise the known clinical, immunological and toxicological consequences of this relationship. While associations between inhaled ambient ultrafine particles and host immune-inflammatory response are known, the airway and environmental microbiomes likely act as intermediaries and facilitate individual susceptibility to inhaled nanoparticles and toxicants. Characterising the precise interaction between the environment and airway microbiomes, inhaled nanoparticles and the host immune system is therefore critical and will provide insight into mechanisms promoting nanoparticle induced airway damage.

An immune cell spray (ICS) formulation allows for the delivery of functional monocyte/macrophages

Macrophages are key cells of the innate immune system and act as tissue resident macrophages (TRMs) in the homeostasis of various tissues. Given their unique functions and therapeutic use as well as the feasibility to derive macrophages in vitro from hematopoietic stem cell (HSC) sources, we propose an “easy-to-use” immune cell spray (ICS) formulation to effectively deliver HSC-derived macrophages. To achieve this aim, we used classical pump spray devices to spray either the human myeloid cell line U937 or primary murine HSC-derived macrophages. For both cell types used, one puff could deliver cells with maintained morphology and functionality. Of note, cells tolerated the spraying process very well with a recovery of more than 90%. In addition, we used osmotic preconditioning to reduce the overall cell size of macrophages. While a 800 mosm hyperosmolar sucrose solution was able to reduce the cell size by 27%, we identified 600 mosm to be effective to reduce the cell size by 15% while maintaining macrophage morphology and functionality. Using an isolated perfused rat lung preparation, the combinatorial use of the ICS with preconditioned and genetically labeled U937 cells allowed the intra-pulmonary delivery of cells, thus paving the way for a new cell delivery platform.

Nanoemulsions in drug delivery: formulation to medical application

Nanoscale oil-in-water emulsions (NEs), heterogeneous systems of two immiscible liquids stabilized by emulsifiers or surfactants, show great potential in medical applications because of their attractive characteristics for drug delivery. NEs have been explored as therapeutic carriers for hydrophobic compounds via various routes of administration. NEs provide opportunities to improve drug delivery via alternative administration routes. However, deep understanding of the NE manufacturing and functionalization fundamentals, and how they relate to the choice of administration route and pharmacological profile is still needed to ease the clinical translation of NEs. Here, we review the diversity of medical applications for NEs and how that governs their formulation, route of administration, and the emergence of increasing sophistication in NE design for specific application.

A review on recent technologies for the manufacture of pulmonary drugs

This review discusses recent developments in the manufacture of inhalable dry powder formulations. Pulmonary drugs have distinct advantages compared with other drug administration routes. However, requirements of drugs properties complicate the manufacture. Control over crystallization to make particles with the desired properties in a single step is often infeasible, which calls for micronization techniques. Although spray drying produces particles in the desired size range, a stable solid state may not be attainable. Supercritical fluids may be used as a solvent or antisolvent, which significantly reduces solvent waste. Future directions include application areas such as biopharmaceuticals for dry powder inhalers and new processing strategies to improve the control over particle formation such as continuous manufacturing with in-line process analytical technologies.

Use of Submicron Vaterite Particles Serves as an Effective Delivery Vehicle to the Respiratory Portion of the Lung

Nano- and microencapsulation has proven to be a useful technique for the construction of drug delivery vehicles for use in vascular medicine. However, the possibility of using these techniques within the lung as an inhalation delivery mechanism has not been previously considered. A critical element of particle delivery to the lung is the degree of penetrance that can be achieved with respect to the airway tree. In this study we examined the effectiveness of near infrared (NIR) dye (Cy7) labeled calcium carbonate (vaterite) particles of 3.15, 1.35, and 0.65 μm diameter in reaching the respiratory portion of the lung. First of all, it was shown that, interaction vaterite particles and the components of the pulmonary surfactant occurs a very strong retardation of the recrystallization and dissolution of the particles, which can subsequently be used to create systems with a prolonging release of bioactive substances after the particles penetrate the distal sections of the lungs. Submicro- and microparticles, coated with Cy7 labeled albumin as a model compound, were delivered to mouse lungs via tracheostomy with subsequent imaging performed 24, 48, and 72 h after delivery by in vivo fluorescence. 20 min post administration particles of all three sizes were visible in the lung, with the deepest penetrance observed with 0.65 μm particles. In vivo biodistribution was confirmed by fluorescence tomography imaging of excised organs post 72 h. Laser scanning confocal microscopy shows 0.65 μm particles reaching the alveolar space. The delivery of fluorophore to the blood was assessed using Cy7 labeled 0.65 μm particles. Cy7 labeled 0.65 μm particles efficiently delivered fluorescent material to the blood with a peak 3 h after particle administration. The pharmacokinetics of NIR fluorescence dye will be shown. These studies establish that by using 0.65 μm particles loaded with Cy7 we can efficiently access the respiratory portion of the lung, which represents a potentially efficient delivery mechanism for both the lung and the vasculature.

Targeted inhibition of Gq signaling induces airway relaxation in mouse models of asthma

Obstructive lung diseases are common causes of disability and death worldwide. A hallmark feature is aberrant activation of G_q protein-dependent signaling cascades. Currently, drugs targeting single G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptors (GPCRs) are used to reduce airway tone. However, therapeutic efficacy is often limited, because various GPCRs contribute to bronchoconstriction, and chronic exposure to receptor-activating medications results in desensitization. We therefore hypothesized that pharmacological G_q inhibition could serve as a central mechanism to achieve efficient therapeutic bronchorelaxation. We found that the compound FR900359 (FR), a membrane-permeable inhibitor of G_q, was effective in silencing G_q signaling in murine and human airway smooth muscle cells. Moreover, FR both prevented bronchoconstrictor responses and triggered sustained airway relaxation in mouse, pig, and human airway tissue ex vivo. Inhalation of FR in healthy wild-type mice resulted in high local concentrations of the compound in the lungs and prevented airway constriction without acute effects on blood pressure and heart rate. FR administration also protected against airway hyperreactivity in murine models of allergen sensitization using ovalbumin and house dust mite as allergens. Our findings establish FR as a selective G_q inhibitor when applied locally to the airways of mice in vivo and suggest that pharmacological blockade of G_q proteins may be a useful therapeutic strategy to achieve bronchorelaxation in asthmatic lung disease.

A compartment-quasi-3D multiscale approach for drug absorption, transport, and retention in the human lungs

Most current models used for modeling the pulmonary drug absorption, transport, and retention are 0D compartmental models where the airways are generally split into the airways and alveolar sections. Such block models deliver low fidelity solutions and the spatial lung drug concentrations cannot be obtained. Other approaches use high fidelity CFD models with limited capabilities due to their exorbitant computational cost. Recently, we presented a novel, fast-running and robust quasi-3D (Q3D) model for modeling the pulmonary airflow. This Q3D method preserved the 3D lung geometry, delivered extremely accurate solutions, and was 25 000 times faster in comparison to the CFD methods. In this paper, we present a Q3D-compartment multiscale combination to model the pulmonary drug absorption, transport, and retention. The initial deposition is obtained from CFD simulations. The lung absorption compartment model of Yu and Rosania is adapted to this multiscale format. The lung is modeled in the Q3D format till the eighth airway generation. The remainder of the lung along with the systemic circulation and elimination processes was modeled using compartments. The Q3D model is further adapted, by allowing for various heterogeneous annular lung layers. This allows us to model the drug transport across the layers and along the lung. Using this multiscale model, the spatiotemporal drug concentrations in the different lung layers and the temporal concentration in the plasma are obtained. The concentration profile in the plasma was found to be better aligned with the experimental findings in comparison with compartmental model for the standard test cases. Thus, this multiscale model can be used to optimize the target-specific drug delivery and increase the localized bioavailability, thereby facilitating applications from the bench to bedside for various patient/lung-disease variations.