A SIMPLE-MODEL BASED ON FIRST-ORDER KINETICS TO EXPLAIN RELEASE OF HIGHLY WATER-SOLUBLE DRUGS FROM POROUS DICALCIUM PHOSPHATE DIHYDRATE MATRICES

A simple model was developed to explain release of highly water solubl e drugs from inert, insoluble, non-swelling porous matrices. According to this model the release can be explained using a first order kineti c expression: Q = Q(0) e(-Kt), where Q is amount released, Q(0) is ini tial amount, and K is rate constant. The rate constant is related to t he geometry of the matrix as: K = K-d A/V where, K-d is a diffusion re lated proportionality constant, A is void area, and V is void volume. For cylindrical matrices, the rate constant can be expressed as K = K- d 2(1/r + 1/h) where r is radius and h is height of the matrix. Cylind rical as well as biconvex matrices were prepared on a single punch tab let machine with varying heights and radii, thus different specific su rface 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 su rface area of the matrices studied.