A theoretical analysis on the controlled release of an active reagent from an inwardly tapered polymeric disk with a central releasing hole proposed originally by Bechard and McMullen (J Pharm Sci 77:222–228, 1988) is conducted. Analytic expressions for the temporal variations in the amount of reagent released and the size of the unreleased portion of the device are derived. Relaxing their assumptions of pseudo-steady and constant reagent concentration in the hole, the problem is reanalyzed. The resultant model is suitable to the whole release period, and successfully describes their experimental data. To make the analytic result derived more readily applicable, the results for some special cases are also presented.
