Release profiles of dexamethasone dipropionate from admixtures of steroid and heparinoid ointments prepared by different mixing methods.

Characterization and release profiles of commercial dexamethasone dipropionate (DDP) from an innovator and 2 generic ointments (Methaderm (IM), Promethasone (GP), and Mainvate (GM)) and their admixtures with heparinoid ointment (Hirudoid Soft) were investigated. The admixtures were prepared using 2 mixing methods (slab or rotation/revolution mixer). Microscopic and FT-Raman spectrometric analyses revealed that the ointments, except for IM, contained DDP crystals. A silicone membrane was used for the evaluation of the DDP permeation. The permeated DDP amounts from GP and GM were lower than that from IM, indicating that DDP solubility in the ointment vehicle affected the release of DDP from the ointment. No significant differences were observed in DDP release between IM alone and its admixture prepared using a slab; however, DDP release from the admixture prepared using a rotation/revolution mixer was significantly lower than those from IM alone and its admixture by slab. In the GP system, DDP release from the admixtures by the 2 mixing methods was higher than that from GP alone, whereas no significant difference in DDP release between the 2 mixing methods was observed. No significant differences were observed between the GM and admixtures. The apparent solubility of DDP in the admixtures as determined by the ultracentrifugal separation method indicated that the DDP amount in the liquid phase of admixtures with GP was 6 times higher than that of admixtures with IM or GM. Therefore, the apparent solubility of DDP in the liquid phase in the GP system might influence the DDP release in admixtures.