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In an attempt to elucidate further physicochemical properties of furosemide-PVP coprecipitates, extensive investigations such as TLC, UV, IR, NMR, X-ray diffraction, TGA and DTA studies were carried out for the furosemide test systems. X-ray diffraction studies revealed that the pure furosemide and the furosemide contained within a physical mixture were crystalline in nature. However, there was no crystallinity evident in the 1:5 furosemide-PVP 40,000 coprecipitate system, even after standing for two years. The various ratio furosemide-PVP 40,000 coprecipitate systems revealed that the coprecipitate containing a greater amount of PVP 40,000 than that of furosemide showed a crystalline state of furosemide and that the minimum amounts of PVP to make amorphous form of furosemide was 1:1 ratio of furosemide to PVP. From the furosemide-PVP coprecipitate systems with PVP of different molecular weights of 10,000, 40,000, and 360,000, all the 1:1 ratio coprecipitates did not exhibit any crystallinity of furosemide, whereas all the 2:1 ratio coprecipitates showed a presence of crystalline furosemide. All the coprecipitated preparations with PEG 4,000 and with PEG 6,000 showed the diffraction peaks indicating the presence of crystalline furosemide. The comparison of infrared spectra of the physical mixture and the coprecipitate showed an interaction such as association between the functional group of furosemide and PVP in the molecular level, whereas the studies by TLC, UV and NMR showed its dissociation in methanol solution. The weight losses in TGA curves showed all the same patterns. However, a little different transition form in DTA thermograms was shown between the physical mixture and the coprecipitate, indicating the different thermal propety.
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