Many years ago I was involved in a capability project to make capsule formulations that contain JUST API. Surprisingly, we got quite close. In one case, we required only the addition of Mag Stearate to keep the dosator from seizing-up; no other excipients were needed. All the desired Physical Properties (bulk density, flow, solid state form) were engineered into a reproducible and scaleable API process. It was a great example of Particle Engineering.
However, it wasn’t a general approach. For the vast majority of cases, delivering not only flowability and density but wettability, dispersion, stability and dissolution with just the API and within the constraints of an advancing project timeline was too big an ask.
I learnt from this experience that the selection of excipients and the unit operations that bring all of these together to create the formulation should be considered as ‘levers’ in the product design alongside Particle Engineering. Doing so provides huge room for manoeuvre in creating the right product without setting unrealistic requirements of the Particle forming step.