Higuchi equation, drug release kinetics

Fick s laws apply for the release kinetics whereas the release of dispersed drugs can be described by Higuchi s equation (1). Release kinetics for both conditions and covering different device geometries were recently reviewed by Baker and Lonsdale (2). 

The drug release profile was plotted against time (Figs. 4 and 5) and it was observed that the release kinetics followed both first-order and Higuchi equations up to 75-80% of the cumulative drug release. The micromatrices followed the Higuchi equation (NONLIN package). 

Release kinetic expression for a tablet (radius rG and thickness /0) can be developed by using Higuchi s pseudo-steady-state approximation and mass balance. With macroscopic observation of the moving boundary of a dispersed drug tablet, Equation (6.76) can be formulated by ... 

In this case, the diffusion of the drug through the core matrix controls the release kinetics. Equation (6.104) is the Higuchi expression. The mathematical expressions for membrane-matrix systems of other geometries can be derived in similar fashion and are shown in Table 6.6. 

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