Self-emulsifying oils for ocular drug delivery. II. In vitro release of indomethacin and hydrocortisone.

The objective of this study was to compare the in vitro release of indomethacin and hydrocortisone from self-emulsifying drug delivery systems (SEDDS) and aqueous or oily suspensions. SEDDS carriers were obtained by dissolving Cremophor EL, Tween 20 or Span 80 in Miglyol oil. The release experiment was performed over 6 h using a dialysis cellulose membrane and acceptor fluid imitating composition of a lacrimal fluid. The release data fitted to the Higuchi's equation. Apparent diffusion constant of indomethacin (k(H)) was in the range 2.55-3.78 mgh(-0.5) and was hardly affected by the formulation type. In the case of hydrocortisone k(H) value was the highest for aqueous and oily suspensions (2.16-2.33 mgh(-0.5)) and for SEDDS systems was not increased even if solubility of the drug was almost 3 times higher than in water or oil. This observation leads to the conclusion that SEDDS does not enhance diffusion rate and other factors can be responsible for the expected better drug absorption through cornea from SEDDS in vivo. Analysis of the release kinetics from sus pension type formulations supports the hypothesis that it may be reasonable to propose SEDDS with the small access of the suspended drug as the most promising formulation.