PHYSICOCHEMICAL ASPECTS OF DRUG RELEASE .10. INVESTIGATION OF THE APPLICABILITY OF THE CUBE ROOT LAW FOR CHARACTERIZATION OF THE DISSOLUTION RATE OF FINE PARTICULATE MATERIALS

The dissolution of some sparingly soluble drugs has been studied to evaluate the cube root law in dissolution testing, especially regarding the applicability of the law for fine particulate materials with varying degrees of polydispersity. It has earlier been shown that the thickness of the diffusion boundary layer around dissolving particles decreases with a decrease in particle size during dissolution. A continuous decrease in mean particle size during dissolution could then be expected to produce a deviation from the cube root law. In contrast to what has been assumed in the literature, the results in this study show that the decrease in mean particle size for fine particulate polydispersed powders is limited during dissolution. Consequently, the dissolution of these materials follows the cube root law. However, it is suggested that the law will not be applicable to strictly monosized materials, for which a continuous decrease in particle size will occur. © 1990.