Invitro Release Study of Sodium Salicylate from Lecithin Based Phospholipid Microemulsions

Sodium salicylate containing microemulsions have been formulated, based on the previous phase diagram studies, using a pharmaceutically acceptable surfactant and oil. The effects of formulation variables on the release profile of the drug from microemulsion through intact rat skin were also determined experimentally. In this investigation, two commercially available lecithins (namely Epikuron 200 and Epikuron 170), three short chain alcohols (n-butanol, isopropanol and n-propanol) and isopropyl myristate (IPM) were used as surfactant, cosurfactant and oil, respectively. The water phase was composed of sodium salicylate solution (2% w/v). To investigate the release profile, samples with 25% wt% total surfactant content were prepared with different surfactant/cosurfactant weight ratios (K_m of 1:1 and 1.5:1) and various amounts of drug solution (from 7 to 35 wt%), depending on the nature of alcohol. Two compartment Franz diffusion cells, equipped with rat skin as the absorption membrane, were employed for release studies. All experiments were performed at room temperature and sampling was taken over 12 hours with one-hour intervals. The amount of drug released was determined spectrophotometrically and the permeation parameters were then calculated. Results showed that systems formulated with 7 and 9% drug solution, were not capable of releasing the drug with a lower rate, compared to the corresponding drug solutions, while in other systems, a lower release rate was observed in comparison to the control samples. In general, among the systems investigated, those prepared with n-propanol at K_m of 1.5:1 and 11-20 wt% and 29% dispersed phase showed a relatively lower absorption rate, comparing to the corresponding control samples , regardless of the nature of surfactant and cosurfactant. Under passive conditions, the flux from microemulsions followed the zero order behavior with respect to the donor concentration.