Crystal growth studies involving phase transitions in aqueous drug suspensions

The growth of oxyclozanide crystals in quiescent suspensions has been monitored using the Coulter Counter. Increase in particle size is the result of an isothermal, solvent-mediated phase transition between two unsolvated polymorphs, one having a lower solubility than the other. Effects due to Ostwald ripening and temperature cycling are absent. Theophylline, which shows crystal growth in suspension by hydration, has been studied by photomicrography. Preliminary results indicate that the initial rate of growth in such systems may be qualitatively described in terms of steady-state diffusion theory.