Multiparticulates can comprise pellets, granules, mini tablets, or mixtures thereof. They may be designed to release drug slowly, rapidly, or following a delay as discussed earlier. Mechanisms underpinning such release are illustrated in Figs. 13.2 and 13.3.
Figure 13.4 illustrates the potential flexibility of multiparticulates for delivering drug in a variety of modes from a single unit. In principle, different drugs with differing release requirements can also be incorporated in such units, allowing simultaneous, sequential, or other such delivery that can be aligned with mode of activity or clinical condition.
Matrix systems control drug release by diffusion- or erosion-mediated kinetics following matrix hydration. An outer coat can also be applied, e.g., to avoid release in the stomach. For example, a core with swelling properties can be coated with an insoluble but water permeable film that ruptures after a defined time for rapid release of drug, thereby providing time-controlled or pulsatile delivery .
Fig. 13.3 Drug release from matrix pellets. (a) Diffusion controlled, (b) erosion controlled
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