Degradation/erosion-controlled drug delivery

DEGRADATION/EROSION-CONTROLLED DRUG DELIVERY SYSTEMS... 

Dissolution, of viscose, 11 254-255 Dissolution-controlled drug delivery, degradation/ erosion-based drug delivery systems, 9 11-19 Dissolution inhibition, by... 

Keywords. Controlled drug delivery, Drug release, Microspheres, Degradation, Erosion, Polylactide, Poly(glycolide-co-lactide), Poly(e-caprolactone), Poly(hydroxyalkanoates) Polyanhydrides, Polycarbonates, Poly(orthoesters), Poly( l,5-dioxepan-2-one)... 

One of the possible solutions to this problem is to use a system of controlled drug delivery in which the drug is released at a constant, preset rate, preferably close to the specific location. One of the most notable approaches is when the drug is contained in a polymer membrane (or encapsulated in a polymer matrix), from which it diffuses out into the tissue in which the membrane/matrix is implanted. In some cases the mechanism of drug release is affected by erosion or polymer dissolution. Degradable polymers such as poly(lactic acid) or polyorthoesters can be used for drug delivery systems of this type [57, 58]. 

Blending is yet another way of manipulating the polymer properties. PTMC degrades too slowly to be useful for most drug delivery applications. Blends were prepared in an attempt to enhance and control the drug delivery rate [121]. Films were prepared from PTMC and poly(adipic anhydride) (PAA), which were partially miscible and formed macroscopically homogeneous blends. The PAA was found to act as a plasticizer and facilitated the erosion of PTMC by increasing the porosity and hydration. PTMC-PAA blends offered sustained and controllable release of an incorporated therapeutic substance as shown in Fig. 11 [121]. 

This degradation process is autocatalytic, since the g-hydroxybutyric acid that is produced catalyzes the hydrolysis reaction. To prevent abrupt degradation and erosion, a basic compound must be incorporated into the polymer. For example, sodium bicarbonate can be incorporated into a polymeric device composed of Alzamer to control the rate of polymer degradation and erosion. Although the polymer has been used for a number of drug delivery applications, it is difficult to produce and requires addition of significant amounts of a basic chemical to prevent uncontrolled degradation [21]. 

Poly(ortho esters) were first developed by the ALZA corporation (Alzamer) in 1970 in order to seek new synthetic polymer for drug delivery applications. These polymers degrade by surface erosion and degradation rates may be controlled by incorporation of acidic or basic excipients. The polymer is hydrophobic enough such that its erosion in aqueous environments is very slow. The unique features of poly(ortho esters), in addition to their surface erosion mechanism, is the rate of degradation for these polymers, pH sensitivity, and glass transition temperatures, which... 

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