Inhalation Biopharmaceutics: Progress Towards Comprehending the Fate of Inhaled Medicines

Integration of mucus and its impact within in vitro setups for inhaled drugs and formulations: Identifying the limits of simple vs. complex methodologies when studying drug dissolution and permeability

Traditionally, developing inhaled drug formulations relied on trial and error, yet recent technological advancements have deepened the understanding of 'inhalation biopharmaceutics' i.e. the processes that occur to influence the rate and extent of drug exposure in the lungs. This knowledge has led to the development of new in vitro models that predict the in vivo behavior of drugs, facilitating the enhancement of existing formulation and the development of novel ones. Our prior research examined how simulated lung fluid (SLF) affects the solubility of inhaled drugs. Building on this, we aimed to explore drug dissolution and permeability in lung mucosa models containing mucus. Thus, the permeation of four active pharmaceutical ingredients (APIs), salbutamol sulphate (SS), tiotropium bromide (TioBr), formoterol fumarate (FF) and budesonide (BUD), was assayed in porcine mucus covered Calu-3 cell layers, cultivated at an air liquid interface (ALI) or submerged in a liquid covered (LC) culture system. Further analysis on BUD and FF involved their transport in a mucus-covered PAMPA system. Finally, their dissolution post-aerosolization from Symbicort® was compared using 'simple' Transwell and complex DissolvIt® apparatuses, alone or in presence of porcine mucus or polymer-lipid mucus simulant. The presence of porcine mucus impacted both permeability and dissolution of inhaled drugs. For instance, permeability of SS was reduced by a factor of ten in the Calu-3 ALI model while the permeability of BUD was reduced by factor of two in LC and ALI setups. The comparison of dissolution methodologies indicated that drug dissolution performance was highly dependent on the setup, observing decreased release efficiency and higher variability in Transwell system compared to DissolvIt®. Overall, results demonstrate that relatively simple methodologies can be used to discriminate between formulations in early phase drug product development. However, for more advanced stages complex methods are required. Crucially, it was clear that the impact of mucus and selection of its composition in in vitro testing of dissolution and permeability should not be neglected when developing drugs and formulations intended for inhalation.

Evolution of pediatric pharmaceutical forms for treatment of Hansen's disease (leprosy)

INTRODUCTION

Leprosy is a neglected, infectious, granulomatous and chronic disease caused by the pathological agent Mycobacterium leprae. The course of the disease is more aggressive in patients under 15 years of age, but the current treatment offered worldwide consists of solid forms, by the combination of antibiotics such as rifampicin, clofazimine and dapsone. This represents results in lack of adherence in pediatric patients and drug therapy failure, although numerous formulations and technologies have already been developed.

AREA COVERED

This study aims to analyze the technological evolution of the pharmaceutical treatment of leprosy, aimed at children. A review of patents around the world was conducted to look for technical and clinical aspects of formulations and devices.

EXPERT OPINION

Innovative formulations for pediatric patients were classified according to the routes of administration as oral, inhalable, injectable and transdermal. The formulations were organized as alternatives for pediatric therapy, taking into account the physicochemical aspects of drugs and the physiological aspects of pediatric patients. Among the difficulties for the patented formulations to reach the market, of special note is the low stability of the physicochemical characteristics of the drugs. Optimization of formulations would favor the pediatric treatment of leprosy, aiming at therapeutic success.

In vitro and ex vivo models in inhalation biopharmaceutical research - advances, challenges and future perspectives

Oral inhalation results in pulmonary drug targeting and thereby reduces systemic side effects, making it the preferred means of drug delivery for the treatment of respiratory disorders such as asthma, chronic obstructive pulmonary disease or cystic fibrosis. In addition, the high alveolar surface area, relatively low enzymatic activity and rich blood supply of the distal airspaces offer a promising pathway to the systemic circulation. This is particularly advantageous when a rapid onset of pharmacological action is desired or when the drug is suffering from stability issues or poor biopharmaceutical performance following oral administration. Several cell and tissue-based in vitro and ex vivo models have been developed over the years, with the intention to realistically mimic pulmonary biological barriers. It is the aim of this review to critically discuss the available models regarding their advantages and limitations and to elaborate further which biopharmaceutical questions can and cannot be answered using the existing models.

Innovating on Inhaled Bioequivalence: A Critical Analysis of the Current Limitations, Potential Solutions and Stakeholders of the Process

Orally inhaled drug products (OIDPs) are an important group of medicines traditionally used to treat pulmonary diseases. Over the past decade, this trend has broadened, increasing their use in other conditions such as diabetes, expanding the interest in this administration route. Thus, the bioequivalence of OIDPs is more important than ever, aiming to increase access to affordable, safe and effective medicines, which translates into better public health policies. However, regulatory agencies leading the bioequivalence process are still deciding the best approach for ensuring a proposed inhalable product is bioequivalent. This lack of agreement translates into less cost-effective strategies to determine bioequivalence, discouraging innovation in this field. The Next-Generation Impactor (NGI) is an example of the slow pace at which the inhalation field evolves. The NGI was officially implemented in 2003, being the last equipment innovation for OIDP characterization. Even though it was a breakthrough in the field, it did not solve other deficiencies of the BE process such as dissolution rate analysis on physiologically relevant conditions, being the last attempt of transferring technology into the field. This review aims to reveal the steps required for innovation in the regulations defining the bioequivalence of OIDPs, elucidating the pitfalls of implementing new technologies in the current standards. To do so, we collected the opinion of experts from the literature to explain these trends, showing, for the first time, the stakeholders of the OIDP market. This review analyzes the stakeholders involved in the development, improvement and implementation of methodologies that can help assess bioequivalence between OIDPs. Additionally, it presents a list of methods potentially useful to overcome some of the current limitations of the bioequivalence standard methodologies. Finally, we review one of the most revolutionary approaches, the inhaled Biopharmaceutical Classification System (IBCs), which can help establish priorities and order in both the innovation process and in regulations for OIDPs.

Drivers of absolute systemic bioavailability after oral pulmonary inhalation in humans

There are few studies in humans dealing with the relationship between physico-chemical properties of drugs and their systemic bioavailability after administration via oral inhalation route (Fpulm). Getting further insight in the determinants of Fpulm after oral pulmonary inhalation could be of value for drugs considered for a systemic delivery as a result of poor oral bioavailability, as well as for drugs considered for a local delivery to anticipate their undesirable systemic effects. To better delineate the parameters influencing the systemic delivery after oral pulmonary inhalation in humans, we studied the influence of physico-chemical and permeability properties obtained in silico on the rate and extent of Fpulm in a series of 77 compounds with or without marketing approval for pulmonary delivery, and intended either for local or for systemic delivery. Principal component analysis (PCA) showed mainly that Fpulm was positively correlated with Papp and negatively correlated with %TPSA, without a significant influence of solubility and ionization fraction, and no apparent link with lipophilicity and drug size parameters. As a result of the small sample set, the performance of the different models as predictive of Fpulm were quite average with random forest algorithm displaying the best performance. As a whole, the different models captured between 50 and 60% of the variability with a prediction error of less than 20%. Tmax data suggested a significant positive influence of lipophilicity on absorption rate while charge apparently had no influence. A significant linear relationship between Cmax and dose (R² = "0.79) highlighted that Cmax was primarily dependent on dose and absorption rate and could be used to estimate Cmax in humans for new inhaled drugs.

Design and development of a biorelevant simulated human lung fluid

Biorelevant fluids are required to enable meaningful in vitro experimental determinations of the biopharmaceutical properties of inhaled medicines, e.g. drug solubility, particle dissolution, cellular uptake. Our aim was to develop a biorelevant simulated lung fluid (SLF) with a well-defined composition and evidence-based directions for use. The SLF contained dipalmitoylphosphotidylcholine, dipalmitoylphosphatidylglycerol, cholesterol, albumin, IgG, transferrin and antioxidants. Freshly made SLF had pH 7.2, viscosity 1.138 × 10⁻³ Pa s, conductivity 14.5 mS/m, surface tension 54.9 mN/m and density 0.999 g/cm³. Colour, surface tension and conductivity were the most sensitive indicators of product deterioration. The simulant was stable for 24 h and 48 h at 37 °C and 21 °C, respectively, (in-use stability) and for 14 days when stored in a refrigerator (storage stability). To extend stability, the SLF was vacuum freeze-dried in batches to produce lyophilised powder that can be reconstituted readily when needed at the point of use. In conclusion, we have reported the composition and manufacture of a biorelevant, synthetic SLF, provided a detailed physico-chemical characterisation and recommendations for how to store and use a product that can be used to generate experimental data to provide inputs to computational models that predict drug bioavailability in the lungs.