Higuchi drug release equation

Higuchi drug release equation can be written also as, Eq. 16.2 ... 

The data were then treated with equation (2), and the cumulative amounts of drug released (0 were plotted against the square root of the time (t1/2) (Fig. 1). Excellent linearity was found, confirming that the release-permeation data followed the Higuchi model. 

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). 

The presence of insoluble ingredients in the formulations helps to maintain the physical dimension of a hydrophobic matrix during drug release. As such, diffusion of the active form from the system is the release mechanism, and the corresponding release characteristic can be described by the Higuchi equation (Eq. 4.11). Very often, pores form within a hydrophobic matrix as a result of the release of the active ingredient. For a porous monolithic system, Eq. (4.11) can be further modified as18... 

When Equation (3) is applied to drug release, the deviations from the exact results are consistently one order of magnitude smaller than those of Higuchi s equation. As A/C >1.04, Equation (3) has an accuracy within 1% of the exact solution. Therefore, Equation (3) is much more accurate than Equation (2), particularly at low A/C values. The latter case occurs quite often in delivery systems involving hydrophilic polymers and drugs of high water solubility. 

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 ... 

For systems where drug release involves the dissolution of a soluble drug at high concentrations from an insoluble matrix, the Higuchi equation adequately describes release rates [Eq. (3)]. 

Drug Release Rate Behavior - Desai et al have reported results of extensive studies on the release of drug from matrices. Taking the basic physical model approach and beginning with the Higuchi relationship these authors have quantitatively investigated the influence of many factors upon the rate of release. The equation was also found by Lapidus and Lordi to apply to a system having hydrophillic gum as the matrix. 

The first step necessary to release the drug is water penetration with formation of a gelified outer layer. For water-soluble cellulose derivatives, both water penetration and drug release are generally controlled by Fickian diffusion and are described by the so-called Higuchi s equations (see e.g. [14]). Recently, we have developed a model that can predict the solute (drug) and penetrant (water) concentration profiles with simultaneous swelling [76] ... 

Drug release from suspension-type semisolid vehicles has been investigated by T. Higuchi (51) and is described by the now classical equation ... 

The next equations, which describe the rate of release of drugs dispersed in an inert matrix system, have been derived by Higuchi [29], The following equation can be written based on Fig. 3 ... 

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. 

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). 

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