Mechanism, drug release from polymer

Drug release from soluble polymers is accompanied by the gradual erosion-type dissolution of the polymer. Therefore, polymer dissolution and drug diffusion may be the overall hybrid mechanism of release. Drug release from nonsoluble hydrogels generally follows Fickian or non-Fickian diffusion kinetics [51]. The mechanism of... 

The classification of polymers for oral drug delivery can be done by using various means. To make this discipline readily accessible to the novice reader, the hydro-phobic-hydrophilic nature of the polymer was chosen to group polymers since the mechanism of biomacromolecule release from most hydrophobic polymeric devices is similar the mechanism of release from most hydrophilic polymeric devices also have similar mechanisms. Hydrophobic polymers are described first, followed by hydrophilic polymers. 

Polymer-based systems. Pulsatile release of medicaments can be obtained from polymer-based delivery systems. Based on the mechanism of drug release from the polymer, these systems can be divided into various classes and subclasses. Broadly, they can be classified into three classes delivery by hydrolysis of polymers, delivery by osmotic pressure, and delivery by both hydrolytic degradation and osmotic effects. 

The mechanisms of drug release from dextran matrix occur in the early stage by polymer swelling, and the tablet thickness increases. Soon thereafter, polymer (and drug) dissolution starts occurring. The polymer dissolves because of chain disentanglement. Thus, there is a slow diminution of the thickness because of erosion until, finally, the tablet disappears (time > 480min). 

Huang, H.-P. Mehta, S.C. Radebaugh, G.W. Fawzi, M.B. Mechanism of drug release from an acrylic polymer-wax matrix tablet. J. Pharm. Sci. 1994, 83, 795-797. 

The mechanism of drug release from hydrophilic matrix tablets after ingestion is complex but it is based on diffusion of the drug through, and erosion of, the outer hydrated polymer on the surface of the matrix. Typically, when the matrix tablet is exposed to an aqueous solution or gastrointestinal fluids, the surface of the tablet is wetted and the polymer hydrates to form a gelly-like structure around the matrix, which is referred to as the gel layer . This process is also termed as the... 

The morphology of polyanhydride was studied by Scanning Electron Microscope (SEM) to elucidate the mechanism of polymer degradation and drug release from polyanhydrides [67]. Microspheres prepared by three different... 

Hydroxypropylmethyl cellulose Hydroxypropyhnethyl cellulose (HPMC) (Figure 28.2) is water-soluble cellulose ether and it can be used as hydrophilic polymer for the preparation of controlled-release tablets. Water penetrates the matrix and hydrates the polymer chains, which eventually disentangle from the matrix. Drug release from HPMC matrices follows two mechanisms, drug diffusion through the swelling gel layer and release by matrix erosion of the swollen layer. " ... 

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