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6854237 
Journal Article 
Solid-state forms of prilocaine hydrochloride - Crystal polymorphism of local anaesthetic drugs, Part II 
Schmidt, AC; Schmidt, AC; Niederwanger, V; Niederwanger, V; Griesser, UJ; Griesser, UJ 
2004 
1 
Journal of Thermal Analysis and Calorimetry
ISSN: 1388-6150
EISSN: 1588-2926 
77 
2 
639-652 
WOS:000223485700023 
Two polymorphic forms, a dioxane solvate and the amorphous form of the local anaesthetic drug prilocaine hydrochloride (N-(2-methylphenyl)-2-propylamino monohydrochloride, PRCHC) were characterized by thermal analysis ( hot stage microscopy, differential scanning calorimetry, thermogravimetry), vibrational spectroscopy ( FTIR, FT-Raman-spectroscopy), powder X-ray diffractometry and water vapor sorption analysis. The formation and thermodynamic stability of the different solid phases is described and presented in a flow chart and an energy temperature diagram, respectively. Mod. Idegrees ( m. p. 169 degreesC) is the thermodynamically stable form at room temperature and present in commercial products. This form crystallizes from all tested solvents except 1,4-dioxane which gives a solvate with half a mole of 1,4-dioxane per mole PRCHC. Mod. II occurs only on desolvation of the dioxane solvate and shows a lower melting point (165.5degreesC) than mod. Idegrees and a lower heat of fusion. Thus, according to the heat of fusion rule, mod. II is the thermodynamically less stable form in the entire temperature range ( monotropism) but kinetically stable for at least a year. Freeze-drying of an aqueous solution leads to the amorphous form. On heating and in moist air amorphous PRCHC exclusively crystallizes to the stable mod. Idegrees. PRCHC exemplifies that certain metastable polymorphic forms are only accessible via a specific solvate, but not via any other crystallization path. Since no crystallization from 1,4-dioxane was performed in earlier solid-state studies of this compound, PRCHC was to this date rated as monomorphic.< 
crystal forms; crystal polymorphism; local anaesthetics; prilocaine hydrochloride; solid-state properties; solvate; thermal analysis 
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