Enhanced design of inhaled therapeutics: what does the future hold?

In vitro-in vivo correlations (IVIVCs) of deposition for drugs given by oral inhalation

Conventional in vitro tests to assess the aerodynamic particle size distribution (APSD) from inhaler devices use simple right-angle inlets ("mouth-throats", MTs) to cascade impactors, and air is drawn through the system at a fixed flow for a fixed time. Since this arrangement differs substantially from both human oropharyngeal airway anatomy and the patterns of air flow when patients use inhalers, the ability of in vitro tests to predict in vivo deposition of pharmaceutical aerosols has been limited. MTs that mimic the human anatomy, coupled with simulated breathing patterns, have yielded estimates of lung dose from in vitro data that closely match those from in vivo gamma scintigraphic or pharmacokinetic studies. However, different models of MTs do not always yield identical data, and selection of an anatomical MT and representative inhalation profiles remains challenging. Improved in vitro - in vivo correlations (IVIVCs) for inhaled drug products could permit increased reliance on in vitro data when developing new inhaled drug products, and could ultimately result in accelerated drug product development, together with reduced research and development spending.

Targeted Treatments for Chronic Obstructive Pulmonary Disease (COPD) Using Low-Molecular-Weight Drugs (LMWDs)

Chronic obstructive pulmonary disease (COPD) is a very common and frequently fatal airway disease. Current therapies for COPD depend mainly on long-acting bronchodilators, which cannot target the pathogenic mechanisms of chronic inflammation in COPD. New pharmaceutical therapies for the inflammatory processes of COPD are urgently needed. Several anti-inflammatory targets have been identified based on increased understanding of the pathogenesis of COPD, which raises new hopes for targeted treatment of this fatal respiratory disease. In this review, we discuss the recent advances in bioactive low-molecular-weight drugs (LMWDs) for the treatment of COPD and, in addition to the first-line drug bronchodilators, focus particularly on low-molecular-weight anti-inflammatory agents, including modulators of inflammatory mediators, inflammasome inhibitors, protease inhibitors, antioxidants, PDE4 inhibitors, kinase inhibitors, and other agents. We also provide new insights into targeted COPD treatments using LMWDs, particularly small-molecule agents.

Spray-Dried PulmoSphere™ Formulations for Inhalation Comprising Crystalline Drug Particles

Over the past 20 years, solution-based spray dried powders have transformed inhaled product development, enabling aerosol delivery of a wider variety of molecules as dry powders. These include inhaled proteins for systemic action (e.g., Exubera®) and high-dose inhaled antibiotics (e.g., TOBI® Podhaler™). Although engineered particles provide several key advantages over traditional powder processing technologies (e.g., spheronized particles and lactose blends), the physicochemical stability of the amorphous drug present in these formulations brings along its own unique set of constraints. To this end, a number of approaches have been developed to maintain the crystallinity of drugs throughout the spray drying process. One approach is to spray dry suspensions of micronized drug(s) from a liquid feed. In this method, minimization of drug particle dissolution in the liquid feed is critical, as dissolved drug is converted into amorphous domains in the spray-dried drug product. The review explores multiple formulation and engineering strategies for decreasing drug dissolution independent of the physicochemical properties of the drug(s). Strategies to minimize particle dissolution include spray blending of particles of different compositions, formation of respirable agglomerates of micronized drug with small porous carrier particles, and use of common ions. The formulations extend the range of doses that can be delivered with a portable inhaler from about 100 ng to 100 mg. The spray-dried particles exhibit significant advantages in terms of lung targeting and dose consistency relative to conventional lactose blends, while still maintaining the crystallinity of drug(s) in the formulated drug product.

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.