CONTROLLED-RELEASE OF DRUGS FROM HYDROCOLLOID EMBEDDINGS

The kinetics of drug release from hydrocolloid embeddings can largely be described by the semi-empirical equation Q/Q(infinity) = k . t(n) b. Drug release ranges from diffusion control (highly viscous polymer matrices) according to Higuchi's root t-law (n = 0.5) over anomalous transport to zero order kinetics (erosion control, n = 1, plane surfac e in both cases). The chain length of the hydrocolloid, the polymer co ncentration and the nature of the added excipients also play a part in the predomination of one mechanism. In general, dehydration leads to a decrease in retardation. In order to explain the constant drug relea se (erosion), one of three models can be consulted dependent on the so lubility of the drug and the properties of the applied polymer. These three models are the diffusion layer, the polymer dissolution and the recently developed particle erosion model. In contrast to the matrix r elease, all three erosion models have in common that the release is fa irly independent of the properties of the drug. Low susceptibility of the release to hydrodynamic stress is generally given with matrix rele ase, or in the case of erosion control with particle erosion. Real Cas e II (relaxation control) or Super Case II release seems unlikely with hydrocolloid embeddings. For the differentiation and confirmation of the release mechanism, swelling numbers (Deborah number, swelling inte rface number, swelling area number) and the time dependence of the dif fusion coefficients can additionally be consulted.