Dissolution Behavior of Indometacin Polymorphs

Abstract

Solubilities and initial dissolution rates of indomethacin polymorphs, pure α and γ forms, in water at various temperatures were determined, and from these parameters and temperatures, the heats of solution, ΔH_2(soln), and heats of dissolution, ΔH_2(diss), of these polymorphs were obtained. The activities of these polymorphs in water were calculated using the ideal solubility equation, and the activity coefficients were also calculated from these activities and mole fraction solubilities. The heats of solution, ΔH_2(soln), of these polymorphs were evaluated using melting points, heats of fusion at the melting points, mole fraction solubilities and activation coefficients. Comparing ΔH_2(soln) with ΔH*_2(soln) or ΔH_2(diss), it was suggested that ΔH_2(soln) corresponded to ΔH_2(diss) rather than to ΔH_2(soln).