Structure XXIII Poly(ethylacrylate, methyl methacrylate) 2 : 1 (Eudragit E 30 D)

XXII and XXIII: Chemical structure of various preparations of Eudragit E range (cationic)

control release of drugs (Fig. 8.29a). Various methods are shown schematically in Table 8.12. If hydrophobic water-soluble polymers are used, the mechanism of release is the passage of drug through pores in the plastic, or by leaching or slow diffusion of drug through the polymer wall (Fig. 8.29b), as discussed earlier in this chapter. Release may also be effected by erosion of the polymer (Fig. 8.29c). When water-soluble polymers are employed, for example as hydrophilic matrices, the entry of water into the polymer is followed by swelling and gelation and the drug must diffuse through the viscous gel, a process obviously slower than diffusion through plain solvent.

Release of drugs from matrices

Equations describing the rate of drug release from hydrophobic and hydrophilic matrices

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