Oral to Inhalable

Efficient delivery of an Active Pharmaceutical Ingredient (API) to the respiratory tract from an inhaler depends on a number of parameters. These include the following:

In order to achieve penetration into the deep lung it is generally accepted that particles of API should ideally have an aerodynamic morphology and a particle size between 1µm and 5µm. Developing such micron sized particles using a conventional ‘top down’ process, like micronisation (also known as milling), results in particles with high surface energy, rough surfaces, amorphous hotspots and defects in the crystal lattice. This causes particles to ‘stick together’, resulting in poor flowability and aerosolation performance. Additionally, particle size is less controlled from such processes, meaning that particle size distributions are wider, which can lead to more drug hitting the back of the throat upon inhalation and being swallowed, or simply being too small and so inhaled and then exhaled immediately with no therapeutic effect.

Crystec’s mSAS® supercritical fluid (SCF) technology, on the other hand, is an appealing alternative when generating powders for inhalation. It is classed as a ‘bottom up’ technology and as such, ‘grows’ particles of the correct size and shape from an organic solution, rather than mechanically grinding larger chunks of material down to the correct size. Particles generated through mSAS® processing are highly crystalline with low levels of electrostatic charge, almost molecularly smooth surfaces and fewer amorphous hotspots. The particle precipitation is thermodynamically controlled and as such particle size is targeted and the particle size distribution very narrow. This means that a greater percentage of the dose emitted from an inhaler upon inspiration reaches the desired site of action in the deep lung, rather than being swallowed or exhaled without therapeutic effect.

An added advantage is that inhaled formulations can be kept very simple because of the ‘in-particle formulation design’ (IPFD) approach taken with mSAS®. Essentially, mSAS® allows Crystec to design particles with inherent performance characteristics (e.g. size and shape for inhalation) to meet a TPP. This ultimately means that complicated formulations aren’t required to overcome the challenges of conventionally prepared powders (e.g. valve lubricants and suspending agents).

Crystec mSAS® Case Study

The focus of this project was to develop an inhalable form of the API with a target particle size of less than 5µm. The aim was to improve the in-vitro Fine Particle Fraction (FPF) as a percentage of Total Emitted Dose (TED) of the API, compared to the micronised starting material. Efficacy was evaluated in-vitro using an Anderson Cascade Impactor (ACI), a mechanical model of the human lung.

The target product profile (TPP) was:

Product Development

Developing the product involved:

Product Analysis and Performance

Particles with an aerodynamic shape and the target particle size were generated. The final formulation was mSAS® powder blended with Respitose (inhalable lactose) due to dosing requirements. It was tested in-vitro using a simple off-the-shelf Dry Powder Inhaler (DPI) device and achieved 68% FPF as a percentage of TED, compared to only 26% for the micronised equivalent. Ongoing accelerated stability studies (40°C/75% relative humidity, 25°C/60% relative humidity) indicate that the formulation is chemically and physically stable at the 24-month time-point.
ACI data for mSAS® and micronised material: drug deposition in the mouth, throat and upper airways are represented on the left half of the graph; deep lung is represented towards the right. The horizontal arrows on x-axis indicate deep lung deposition (higher delivery in this area is better).
Scanning Electron Microscope image of mSAS® product at x5000 magnification. Image shows crystals with smooth, undamaged surfaces and slightly rounded edges.

Sympatec laser particle size analysis (PSA) data showing three repeat batches of SCF product. Image shows both a tight distribution of particles in the inhalable size range and a highly reproducible product.