PHYSICAL CHARACTERIZATION OF SOLID FORMS OF CYCLOPENTHIAZIDE

Three polymorphic forms of cyclopenthiazide were prepared and characterised by DSC, thermomicroscopy, X-ray powder diffraction, scanning electron photomicrographs, IR, solid-state C-13-NMR, solution calorimetry, elementary analysis, intrinsic dissolution, powder dissolution and solubility determinations. Form II has the highest solubility in both 0.01 M HCl and 0.01 M NaOH. It was shown to be metastable in these solvents. When heated continuously, form III melts at 181-degrees-C and then recrystallises to form I. Form III is the least soluble in water, 0.01 M HCl and 0.01 M NaOH. Form I has an intermediate solubility in these three solvents and is enantiotropic.