(i) initial
drug concentration in the matrix is much higher than
drug solubility; (ii) drug diffusion takes place only
in one dimension (edge effect must be negligible);
(iii) drug particles are much smaller than system
thickness; (iv) matrix swelling and dissolution are
negligible; (v) drug diffusivity is constant; and (vi)
perfect sink conditions are always attained in the
release environment. Accordingly, model expression
is given by the equation: