Fractional drug release vs. time

These observations indicate that almost the entire set of data listed in Table 

2 and generated from (4.11) can be misinterpreted as obeying (4.3). Under real experimental conditions the discernment of kinetics is even more difficult when linear regression of q (t) /g,Xj vs. t1/2 is applied. This is so if one takes into account 

Therefore, it is advisable to fit (4.11) directly to experimental data using nonlinear regression. Conclusions concerning the release mechanisms can be based on the estimates for A and the regression line statistics [69]. 

Although the emphasis of this section will be on the most recent mechanistic approaches, the work of Fu et al. [70] published in 1976 should be mentioned since it deals with the fundamental release problem of a drug homogeneously distributed in a cylinder. In reality, Fu et al. [70] solved Fick s second law equation assuming constant cylindrical geometry and no interaction between drug molecules. These characteristics imply a constant diffusion coefficient in all three dimensions throughout the release process. Their basic result in the form of an analytical solution is 

Gao et al. [71, 72] developed a mathematical model to describe the effect of formulation composition on the drug release rate for hydroxypropyl methylcellulose-based tablets. An effective drug diffusion coefficient T , was found to control the rate of release as derived from a steady-state approximation of Fick s law in one dimension  

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