Crystal modification of phenytoin using different solvents and crystallization conditions.

Phenytoin crystals having different types of habits, were prepared by recrystallization from ethanol and acetone solutions under different conditions (cooling rate or crystallization temperature, solvent evaporation and watering-out techniques). Scanning electron microscopy, X-ray powder diffractometry, FT-IR spectrometry and differential scanning calorimetry were used to investigate the physical characteristics of the crystals. The dissolution behavior and compaction properties of various batches of crystals were also studied. It was found that using watering-out technique as a crystallization method, produced thin plate crystals, while the crystals obtained by other methods were needle shape for alcoholic solutions and rhombic for acetone solutions. X-ray diffraction spectra and differential scanning calorimetry studies, did not show any polymorphic change. The dissolution rate of different crystals was lower than that of untreated samples. The compacts of phenytoin crystals produced from alcohol or acetone (especially those made by watering-out method) had higher crushing strengths than untreated phenytoin compacts due to the lower porosity and the lower elastic recovery.