Case II drug transport with axial and radial release from a cylinder

After integration of (4.7), we obtain the following equations as well as the time for which each one is operating  

This means that the smaller dimension of the cylinder (p or L) determines the duration of the phenomenon. 

The amount of drug released at any time t is given by the following mass-balance equation  

Substituting (4.8) into (4.9), the following expression for mass q (t) as a function of time t is obtained  

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Figure 4.2 Case II drug transport with axial and radial release from a cylinder of height 2L and radius p at t = 0. Drug release takes place from all sides of the big cylinder. The drug mass is contained in the grey region. After time t the height of the cylinder is reduced to 2L and its radius to p (small cylinder).

This equation describes the entire fractional release curve for Case II drug transport with axial and radial release from a cylinder. Again, (4.10) indicates that the smaller dimension of the cylinder p or L) determines the total duration of the phenomenon. When p> L, (4.10) can be approximated by... 

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