Matrix Diffusion Controlled Systems ?

Matrix Diffusion Controlled Systems :

Here, the drug is dispersed in an insoluble matrix of rigid non swell able hydrophobic materials or swell able hydrophilic substances. Materials used for rigid matrix are insoluble plastics such as PVC and fatty materials like stearic acid, beeswax, etc. With plastic materials, the drug is generally kneaded with the solution of PVC in an organic solvent and nucleated. Waxy matrix is prepared by dispersing the drug in molten fat followed by congealing. The granules are then compressed into tablets.

Swellable matrix systems are popular for sustaining the release of highly water-soluble drugs. The material for such matrices are generally hydrophilic gums and may be of natural origin (guar gum, tragacanth),semi-synthetic (HPMC, CMC, xanthan gum) or synthetic (polyacrylamides).

The drug and the gum are granulated together with a solvent such as alcohol and compressed into tablets. The release of drug from such initially dehydrated hydro-gels involves simultaneous absorption of water (resulting in hydration, gelling and swelling of gum) and absorption of drug via a swelling controlled diffuse mechanism. As the gum swells and the drug diffuses out of it, the swollen mass, devoid of drugs appears transparent or glass like and therefore the system is sometimes called as glassy hydro-gel,

The drug release follows Fickian's first-order diffusion under equilibrium conditions. I However, during the swelling process, such an equilibrium may not exist and the diffusion may be non-Fickian's or anomalous diffuse.