Figure 4.

Osmotic-release drug delivery systems. These systems consist of the drug and an osmotic agent surrounded by a semipermeable membrane capsule containing a small orifice. (A) In single chamber capsules, water is drawn into the capsule by the osmotic agent, which begins to swell, forcing the drug through the orifice. (B) Double-chamber capsules have an additional push chamber containing a highly swellable polymer. As this polymer swells, the push chamber expands, exerting pressure on the drug-containing chamber, forcing the drug through the orifice.