Suspension pellet layering using PVA–PEG graft copolymer as a new binder

Flow characteristics and binding properties of Kollicoat ® IR solutions are promising for an application in suspension layering processes to obtain drug loaded pellets. This study is based on the results of three experimental designs. Within the first one, a suitable binder concentration in suspensions with 35–45% solids was determined. The required binder level was high with 20% in the layer, but led to good and robust process performance with a yield between 92.6% and 97.6%. Since the polymer succeeded to immobilize particles on the starter surface, the second set of experiments observed whether Kollicoat ® IR was able to layer coarser drug particles with only 8% or 30% of the drug mass below ten microns. Large particle size is a generally known limitation for effective suspension layering. It was shown, that Kollicoat ® IR was suited to bind 98.5% of the coarsest drug quality on the surface. Additionally these coarse particles acted like a separating agent and kept the pellets from sticking to each other. The third experimental design observed the influence of particle size and viscosity changes. All suspensions had a suitable viscosity with maximum of 120 mPa s. A viscosity change, due to solids in the suspension, did not influence the process performance. The product properties were investigated. The pellets were spherical and size distribution of the pellets was excellent. However the structure was porous, due to the sterical arrangement of the drug particles, although the polymer concentration in the layer was high with a polymer to drug ratio of 1:4.