Abstract
Background: Cannabidiol (CBD) is a non-intoxicating phytocannabinoid with potent antiepileptic, anxiolytic, immunomodulatory, anti-inflammatory, and neuroprotective properties. Its therapeutic potential has been explored across numerous conditions, including seizures, inflammation, cardiovascular diseases, chronic obstructive pulmonary disease, and asthma. Despite its promising pharmacological properties, the clinical utility of orally administered CBD is limited by its extremely low and highly variable bioavailability, primarily due to its poor aqueous solubility, extensive first-pass hepatic metabolism, and variable pharmacokinetics.
Formulation strategies and various administration routes can overcome many of these limitations, enhancing CBD’s solubility, dissolution, absorption, and systemic exposure. Pulmonary delivery has emerged as a highly attractive route for both local and systemic CBD delivery, owing to the lungs' large absorptive surface area, rapid drug uptake, avoidance of first-pass metabolism, and suitability for treating lung-specific diseases. Delivering CBD as an inhalable dry powder formulation may enable therapeutically effective concentrations in the lungs. However, developing such formulations is challenging due to CBD’s lipophilicity, adhesive properties, and the inherent cohesiveness of micron-sized particles required for optimal pulmonary deposition.
Therefore, this thesis investigates the development of CBD dry powder formulations for the treatment of inflammatory lung diseases, evaluates the impact of different particle-engineering techniques on powder characteristics, and examines the influence of excipients on physicochemical, aerosolization, and efficacy of these formulations.
Methods: The particle-engineering techniques varied across chapters, whereas the characterization methods remained largely consistent and are described in Chapter 3. Across all chapters, the prepared powders were characterized using scanning electron microscopy (SEM) for particle morphology and size, thermogravimetric analysis for residual solvent content, powder X-ray diffraction (pXRD) for crystalline behavior, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy for drug-excipient interactions. Stability studies were performed at 25°C/<15% RH and 25°C/53% RH for 28 days. In vitro studies included aerosolization performance using a Next Generation Impactor (NGI), cytotoxicity by MTT assay in alveolar basal epithelial cells (A549), and anti-inflammatory effect by the capability of CBD to reduce the inflammation caused by lipopolysaccharide (LPS) using an enzyme-linked immunosorbent assay (ELISA) kit (Chapters 4, 6, and 7). In Chapter 4, CBD dry powder formulations were prepared by spray-drying using inulin and L-leucine. In Chapter 5, the optimized formulation from Chapter 4 was investigated by replacing L-leucine with different amino acids (lysine, phenylalanine, cysteine, and arginine) to evaluate their impact on the powder's physicochemical and aerosolization properties. In Chapter 6, CBD was formulated with kaempferol and L-leucine using spray drying to assess whether kaempferol could enhance CBD's aerosolization, cytotoxicity, and anti-inflammatory activity. In Chapter 7, spray-freeze drying was explored as an alternative particle-engineering technique, using mannitol, inulin, and L-leucine to prepare CBD dry powder formulations. In Chapter 8, CBD powders were prepared using ball milling with mannitol, trehalose, and L-leucine.
Results: Spray-dried powders in Chapters 4-6 exhibited spherical, crystalline particles within the respirable 1–5 µm range. Increasing the concentration of L-leucine enhanced aerosolization, with the highest fine particle fraction (FPF) of 62% at 20% w/w L-leucine (Chapter 4). These formulations remained stable for 28 days, and both raw CBD and CBD dry powders showed similar cytotoxicity (pIC₅₀: 4.2 - 4.5). Amino acid–free CBD produced irregular, flaky particles, whereas amino acid–containing powders produced spherical and dimpled particles (Chapter 5). The use of all amino acids with CBD enhanced aerosolization of CBD, with lysine-containing powders achieving the highest FPF of 56.6%. Similarly, the use of kaempferol with CBD enhanced aerosolization, yielding FPF values of 60.3 ± 1.0% (Chapter 6). The CBD-kaempferol combination maintained high cell viability (87%) while demonstrating anti-inflammatory potency comparable to that of raw CBD. Spray-freeze drying successfully produced inhalable CBD powders, with L-leucine–containing formulations achieving the highest aerosolization (FPF 67% and 62%) and anti-inflammatory activity (pEC₅₀ ≈ 4.9) (Chapter 7). Both excipient composition and milling duration influenced the aerosolization properties of ball-milled powders (Chapter 8). The mannitol–leucine–CBD formulation showed the highest aerosol performance among the milled powders (FPF 47%).
Conclusions: The findings demonstrate that inhalable CBD dry powder formulations were successfully produced using spray-drying, spray-freeze drying, and ball milling. Excipients, particularly L-leucine, were essential for enhancing aerosolization performance and maintaining physicochemical stability under 25°C/<15% RH and 25°C/53% RH humidity conditions. Importantly, all CBD formulations retained acceptable cytotoxicity profiles and preserved anti-inflammatory activity. Overall, this work establishes inhalable CBD dry powders as a promising strategy for pulmonary delivery of CBD for the treatment of inflammatory pulmonary diseases by demonstrating favorable aerosolization performance, physicochemical stability under relevant storage conditions, and preserved in vitro anti-inflammatory activity. These formulations warrant further investigation into preclinical animal models to confirm their therapeutic potential and support their progression toward clinical development.