Characterization of hydrates of norfloxacin

Norfloxacin, a nalidixic acid analog with antimicrobial properties, exists in different hydrated forms. Three of these crystal forms were reproducibly prepared and characterized by analytical techniques that included infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, solution microcalorimetry and pulsed nuclear-magnetic resonance spectroscopy.These studies showed that the dihydrate is the thermodynamically stable entity at ambient temperatures and humidities.