Page 193 - Biomedical Engineering and Design Handbook Volume 2, Applications

172 MEDICAL DEVICE DESIGN

Time (t) = 0 h t = t h (in the gut lumen)
1
Laser-drilled orifice Zero-order drug release
Semipermeable coat
Drug and excipients

Push layer (water
Push layer expands
swellable polymer)

Laser-drilled orifice Zero-order drug release
Semipermeable coat
Drug, osmotic agents, and Drug solution containg
solubility enhancers osmotic agents and
water swellable
Wicking agent (water
polymers
swellable polymer)

Zero-order drug release
Immediate release coat Semipermeable coat
Laser-drilled orifice
Drug and excipients
Semipermeable coat
Push layer (water Push layer expands
swellable polymer)

Laser-drilled orifice
Zero-order drug release
Semipermeable coat
Drug and excipients Semipermeable coat
Release delay coat

Push layer (water Push layer expands
swellable polymer)
FIGURE 6.5 Schematic illustration of various mechanisms of osmotic-controlled release dosage forms.

If the osmotic pressure difference is much larger than the hydrostatic pressure difference (Δπ>> ΔP ),
the equation can be simplified to

dV ⎛ AK ⎞
= (Δπ ) (6.18)
dt ⎝ h ⎠