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Oral Sustained and Controlled-Release Products

Due to their reactive ease of production and cost compared to other  methods of sustained or controlled delivery, the dissolution and  diffusion-controlled systems have classically been of primary  importance in oral delivery of medication. Dissolution systems  have been some of the oldest and most successful oral systems in  early attempts to market sustaining products.



1- Diffusional Systems:

Diffusional systems are characterized by the release rate of  drug being dependent on its diffusion through an inert membrane barrier. Usually, this barrier is an insoluble  polymer. In general, two types are recognized: reservoir devices and matrix devices.

A) Reservoir Devices
Reservoir devices are characterized by a core of drug, the  reservoir, surrounded by a polymeric membrane. The  nature of the membrane determines the rate of release of  drug from the system. 
The process of diffusion is generally described by a series  of equations that were first described by Fick and hence retain his name. 

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