Dissolution behavior of solid drugs. V. Determination of the transition temperature and heat of transition between barbital polymorphs by initial dissolution rate measurements.

Abstract

Transition temperature and heat of transition between barbital forms I and II were found to be 93° and 210 cal/mole, respectively, measuring their initial dissolution rates by the method reported in the previous paper. The latter value is reasonably close to the value of 330±15 cal/mole obtained by differential scanning calorimetry (DSC). The data obtained in this study indicates that forms I and II are enantiotropic contrary to such a statement appeared in literature as they are monotropic. Furthermore, it was found that there is little difference in solubility values of barbital forms I and II.