Crystallization of hydrocortisone acetate: influence of polymers.

The influence of hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG400) on the crystallization of hydrocortisone acetate (HA) was studied. Supersaturation was created by the cosolvent technique. Spontaneous nucleation was observed when no polymer was used as the additive. In the presence of the polymer, nucleation was delayed. The nucleation time decreased with increasing supersaturation at a particular polymer concentration and increased with increasing polymer concentration at a particular supersaturation. Habit modification from a well-defined polar prismatic morphology to a wing-shaped morphology was observed when HPMC was used as the additive. The effect of PVP and PEG400 on the morphology of HA was less pronounced compared to the cellulose polymers. The mechanism of nucleation retardation by the polymers is explained in terms of association of HA with the polymer through hydrogen bonding. The growth may be inhibited by the hydrodynamic boundary layer, in which the polymers accumulate as well as by the adsorption of the polymer onto the crystal surface. The habit modification of HA by HPMC is due to different extents of adsorption on different faces of the crystal, the extent of which is dependent on the hydrogen bonding functional groups that are exposed at each face of the crystal.