An osmotic delivery system has a membrane plug retention mechanism which can
also
be used to control the delivery rate of a beneficial agent from the osmotic delivery
system. The osmotic delivery device includes an implant capsule containing a beneficial
agent and an osmotic agent. Holes are formed along a side wall of the implant capsule
at an open end of the capsule. When the membrane plug is inserted into the open
end of the capsule, the membrane material swells into the holes in the capsule
side wall creating a large frictional force which prevents expulsion of the membrane
plug. A beneficial agent delivery rate of the osmotic delivery system is controllable
by varying the size and number of the holes to change the amount of exposed surface
area of the membrane plug. An increase in the surface area of the membrane plug
exposed to the exterior environment causes a corresponding increase in the liquid
permeation rate of the membrane and thus, increases the beneficial agent delivery rate.
