Influence of solvent and crystallization method on the crystal habit of metronidazole.

In the present study, metronidazole was crystallized in several solvents, according to both the "cooling crystallization" and the "crystallization by non-solvent addition". Particle properties, such as crystal habit, elongation ratio, and mean particle size, were determined by SEM analysis. Structural changes and development of polymorphic forms were excluded by both Differential Scanning Calorimetry (DSC) and X-Ray Powder Diffractometry (XRPD). Crystal habit (and thus elongation ratio) was typically influenced by both the solvent polarity index and the crystallization method: solvents with higher polarity index tended to promote acicular or stick-shaped crystals with a high elongation ratio, while isodimensional crystals were promoted by decreasing the polarity index, as was particle aggregation.