Stability studies of pramipexole dihydrochloride performed under following conditions of temperature and relative humidity (RH): 25 degrees C 60% RH and 40 degrees C 75% RH revealed its tendency to the water sorption and the monohydrate formation. The structural changes occurring during storage were studied by infrared spectroscopy and X-ray powder diffraction methods. The thermogravimetry technique was used to control the water sorption by the substance. Pramipexole dihydrochloride monohydrate was characterized by nuclear magnetic resonance and X-ray single crystal diffraction methods. The monohydrate crystallizes in the orthorhombic crystal system in the space group P212121.
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