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The Physico-Chemical Properties of Glipizide: New Findings
Authors:Giovanna Bruni  Ines Ghione  Vittorio Berbenni  Andrea Cardini  Doretta Capsoni  Alessandro Girella  Chiara Milanese  Amedeo Marini
Affiliation:1.C.S.G.I.—Department of Chemistry, Physical-Chemistry Section, University of Pavia, Via Taramelli 16, 27100 Pavia, Italy; (I.G.); (V.B.); (D.C.); (A.G.); (C.M.); (A.M.);2.A.M.S.A. Anonima Materie Sintetiche Affini S.p.A., Viale Giuseppe Di Vittorio 6, 2100 Como, Italy;
Abstract:The present work is a concrete example of how physico-chemical studies, if performed in depth, are crucial to understand the behavior of pharmaceutical solids and constitute a solid basis for the control of the reproducibility of the industrial batches. In particular, a deep study of the thermal behavior of glipizide, a hypoglycemic drug, was carried out with the aim of clarifying whether the recognition of its polymorphic forms can really be done on the basis of the endothermic peak that the literature studies attribute to the melting of the compound. A number of analytical techniques were used: thermal techniques (DSC, TGA), X-ray powder diffraction (XRPD), FT-IR spectroscopy and scanning electron microscopy (SEM). Great attention was paid to the experimental design and to the interpretation of the combined results obtained by all these techniques. We proved that the attribution of the endothermic peak shown by glipizide to its melting was actually wrong. The DSC peak is no doubt triggered by a decomposition process that involves gas evolution (cyclohexanamine and carbon dioxide) and formation of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which remains as decomposition residue. Thermal treatments properly designed and the combined use of DSC with FT-IR and XRPD led to identifying a new polymorphic form of 5-methyl-N-[2-(4-sulphamoylphenyl) ethyl] pyrazine-2-carboxamide, which is obtained by crystallization from the melt. Hence, our results put into evidence that the check of the polymorphic form of glipizide cannot be based on the temperature values of the DSC peak, since such a peak is due to a decomposition process whose Tonset value is strongly affected by the particle size. Kinetic studies of the decomposition process show the high stability of solid glipizide at room temperature.
Keywords:glipizide   differential scanning calorimetry   thermogravimetric analysis   decomposition   polymorph   5-methyl-N-[2-(4-sulphamoylphenyl)ethyl]pyrazine-2-carboxyamide   kinetic study   shelf-life
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