ISOENERGETIC POLYMORPHS

Polymorphs are attracting a great deal of attention in present-day pharmaceutical literature. Most often the polymorphic forms are distinguished by way of solubility (or dissolution rates), DSC and X-ray diffraction. The writing to follow deals with a polymorphic pair which is virtually indistinguishable except by means of X-ray diffraction, and the essence of the report is that failing to show significant differences in solubility, and ob serving no, or only slight differences in melting point (which could be due to impurities) is not sufficient to rule out polymorphism(1-6). The compound N-[2-{{{-5-{(Dimethylamino)methyl]-2-furanyl]thio]ethyl-N'-methyl-2 -nitro-1,1-ethenediamine hydrochloride, present in two polymorphic forms, I and II, is used as a model compound.