Crystalline particles that have needle or plate shapes can be approximated by long or shallow cylinders. By making such an approximation the cube root equation may be solved for non-isometric shapes and the effect of the degree of isometricity on the length of time the cube root dissolution equation will hold has been derived. A more exacting method of plotting is presented allowing calculation of the intrinsic dissolution rate constant from the slope of a plot of a reduced time plotted versus actual time.