Characterization of the polymorph changes in Trimethoprim

Polymorphic transformation in Trimethoprim (TMP) drug has been studied employing differential scanning calorimetry (DSC), TG/DSC, X-ray diffraction and FTIR techniques. To obtain a better understanding of the thermal events for the TMP polymorphs, a series of increasing heating rates and different mass were used. DSC of the Trimethoprim indicated that the as-received sample was crystalline (Form A). The molten Trimethoprim on cooling, however, produced a glassy amorphous mass. The sample obtained after heating at 100 A degrees C for 1 h transformed to Trimethoprim (Form B).The glass transition observed in the second heating at 61 A degrees C was followed by crystallization of the product at 81 A degrees C. Form B of this study is probably a novel TMP polymorph.