An osmotic pump is best described as which type of controlled-release system?

• A. Monolithic matrix
• B. Reservoir with a rate-controlling membrane
• C. Diffusion-controlled reservoir
• D. Osmotically driven reservoir with semipermeable membrane

Answer: (B)

An osmotic pump delivers drug from a central reservoir by an osmotically generated pressure, controlled by a semipermeable membrane surrounding the drug core. Water from the GI tract permeates through that membrane, builds hydrostatic pressure, and pushes the drug out through a small delivery orifice at a nearly constant rate. This architecture—drug confined in a reservoir and release rate governed by a rate-controlling membrane—best matches the osmotic pump concept. It differs from monolithic or diffusion-controlled systems, where release is driven mainly by diffusion through a matrix rather than by osmosis and a controlled barrier.