Compositions of particulate coformulation

A method of preparing a particulate co-formulation, the method comprising:

• (i) dissolving an active substance and an additive in a vehicle to form a single phase target solution;
• (ii) co-introducing into a particle formation vessel, (a) a supercritical fluid that is miscible in all proportions with the vehicle and in which the active substance and the additive are insoluble or substantially insoluble, and (b) the target solution, such that the supercritical fluid and target solution enter the vessel at the same point and under conditions effective to disperse the target solution in the supercritical fluid and extract the vehicle therefrom, to thereby form a co-precipitated particulate product that is a solid dispersion of the active substance and the additive,
• wherein the particles of the particulate product have a finite gradient in relative additive concentration that increases radially outwards from the core to the surface of the particles, such that the particles comprise an additive-rich surface region but do not possess separate core and coating layers with a distinct physical boundary between them.