Polymer matrix diffusion-controlled drug

Polymer matrix diffusion-controlled drug delivery systems. 

Polymer Matrix Diffusion-Controlled Drug Delivery Systems... 

Details are given of pilocarpine trapped in a matrix diffusion-controlled drug delivery system using hydrophilic inserts of polyhydroxyethyl methacrylate. The physical and chemical properties of pilocarpine were investigated to determine the mechanism of drug-polymer interaction and the effect of drug release behaviour of controlled release polymeric devices. 22 refs. 

Matrix diffusion-controlled system in which the drug is homogeneously dispersed in a hydrophilic polymer diffusion from the matrix controls release rate Nitrodur (nitroglycerin key). 

Polyvinyl acetate (PVAc) is a homopolymer synthesized from vinyl acetate monomer using a free radical polymerization procedure [25]. This water-insoluble polymer is mostly employed blended with other polymers. The most famous association is the physical mixture of PVAc and polyvinyl pirrolidone (PVP), commercially known as Kollidon SR by the chemical company BASF. Kollidon SR consists of 80% PVAc, 19% of PVP and 1% of sodium lauryl sulfate and silica as stabilizers (BASF). The PVP is added as water-soluble polyamide which forms pores into the matrix tablet allowing drug diffusion. Kollidon SR has been shown to be a suitable pH-independent excipient to form matrix tablets, controlling drug release by both diffusion and erosion mechanisms [24]. 

The rate of drug release (E) from the eroding matrix is controlled by (a) the chemical properties of the system - the hydrolytic and the neutralizing process at the boundary of the device, catalytic degradation of the polymer and the intrinsic backbone reactivity, and (b) several concomitant physical processes such as water diffusivity, water solubility, water partitioning, etc. 

Diffusion-controlled membranes exist in two categories depot systems, in which the drug is totally encapsulated within a reservoir, and monolithic systems, where the drug is dispersed in a rate-controlling polymer matrix [25]. One commercially successful depot device is the Alza Ocusert for ocular delivery of pilocarpine in the treatment of glaucoma [25]. 

Controlled release of a chemical substance can be effected by diffusion or erosion of a polymer matrix ( 1). This method has been used with considerable success in the delivery of bioactive compounds in agriculture and, to some extent, in dispensing drugs by absorption through tissue upon contact. 

For swelling-controlled systems the swelling of the polymer matrix after the inward flux of the liquid bathing the system induces the diffusion of drug molecules towards the bathing solution. 

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