Utilization of osmotic pressure as a driving force for delivery of pharmaceutical agents in a controlled pattern for a prolonged period

agents in a controlled pattern for a prolonged period of time is a well-established fact. The concept of osmotic drug delivery was first introduced by Theeuwes (1). The simplest design of an osmotic drug delivery system consists of an osmotically active core surrounded by a semipermeable membrane, with one or more delivery orifices through which the drug is delivered in a controlled fashion. Various modifications of the basic design of osmotic pump have been reported (2) and reviewed (3, 4). One such modification is the utilization of asymmetric membrane coating for osmotic drug delivery. The walls of an asymmetric membrane capsule are prepared by the phase inversion technique. As the name suggests, the membrane is asymmetric in nature, i.e., it has a relatively thin dense region supported on a thicker porous region (5).