Preparation of spherically agglomerated crystals of aminophylline

The spherically agglomerated crystals of aminophylline (theophylline-ethylenediamine complex) can be compounded directly into pharmaceutical formulations without further processing, e.g., granulation. Such crystals were prepared by mixing theophylline and ethylenediamine in a partially miscible solvent system, i.e., organic solvent-ethanol-water. The organic solvents used were chloroform, 1-hexanol, isopropyl acetate, isobutyl acetate, isoamyl acetate, benzene, toluene, n-hexane, or n-heptane. Spherical crystallization depended upon the solubility of theophylline in the solvent mixture. The resultant agglomerated crystals were identical with the theophylline-ethylenediamine complex by IR, X-ray, and differential scanning calorimetry analyses, and was the alpha-, beta-, or gamma-form when the water of crystallization was less than or equal to 0.5, 1.0, and 2.5 mol, respectively. When the amount of ethylenediamine used was less than 1.1 mL (0.0165 mol), the resultant agglomerated crystals were converted to anhydrous theophylline by washing with ethanol. When water was added to the system (greater than or equal to 0.3 mL, i.e., 0.0167 mol), water was occluded in the resultant agglomerates as water of crystallization. Ethylenediamine content in the agglomerated crystals could be controlled by changing the amount of ethylenediamine added in the crystallization solvent.