Formulation study of oxybutynin patches.

The present feasibility study was designed to obtain a monolayer patch containing oxybutynin (OXY) avoiding chemical permeation enhancers. The highest flux was obtained with a polydimethylsiloxane matrix patch. Because OXY crystals were detected in the matrix within a week, two amino methylmethacrylate copolymers (Eudragit E or Eudragit RS) were used as OXY crystallization inhibitors. A preliminary in vivo study indicated that flux from the stabilized patches had to be increased about 30-40%. This goal was reached by occlusion with a polyethylene layer.