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Purpose: The purpose of this presentation was to clarify the quantitative relation between the initial dissolution rates and heat of solution of drug substances, and the quantitative evaluation of surface properties of drug substances by the liquid penetration rate measurement.Methods: The initial dissolution rates of amorphous, partial crystalline and crystalline samples of terfenadine polymorphs (form Ⅰ and form Ⅱ) were measured by the rotating disk method.The heat of solution was obtained by isothermal microcalorimetry.The heats of fusion due to crystalline fraction of samples were obtained by the differential scanning calorimetry (DSC).The surface free energy of phenytoin crystals with different crystallization conditions was measured by the capillary penetration technique.Results: The logarithms of initial dissolution rates of different crystallinity samples were linearly correlated with the heat of solution and/or corrected heat of fusion, irrespective of the crystal forms.The dissolution rate of phenytoin powder was affected by the surface properties and the more hydrophilic surface accelerates the dissolution of phenytoin powder.Conclusion: The quantitative evaluation of crystallinity and surface property is important to control the dissolution of drug substance.