A Simple Model Based on First Order Kinetics to Explain Release of Highly Water Soluble Drugs from Porous Dicalcium Phosphate Dihydrate Matrices

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Abstract
A simple model was developed to explain release of highly water soluble drugs from inert, insoluble, nonswelling porous matrices. According to this model the release can be explained using a first order kinetic expression: Q = Qo e-Kt, where Q is amount released, Qo is initial amount, and K is rate constant. The rate constant is related to the geometry of the matrix as: K = Kb A/V where, Kb is a diffusion related proportionality constant, A is void area, and V is void volume. For cylindrical matrices, the rate constant can be expressed as K = Kb 2(1/r + 1/h) where r is radius and h is height of the matrix. Cylindrical as well as biconvex matrices were prepared on a single punch tablet machine with varying heights and radii, thus different specific surface areas. The rate constants were determined following dissolution testing. The experimental release profiles follow first order kinetics. Good correlation was found between the rate constant and specific surface area of the matrices studied.