LECITHIN-STABILIZED MICROEMULSION-BASED ORGANOGELS FOR TOPICAL APPLICATION OF KETOROLAC TROMETHAMINE. II. IN VITRO RELEASE STUDY

Ketorolac tromethamine (KT) containing microemulsion-based gels (MBGs) have been formulated, based on the previous phase diagram studies, using a pharmaceutically acceptable surfactant (soybean lecithin; Epikuron 200) and oil (isopropyl myristate; IPM) and the effect of formulation variables on the release profile of the drug from MBGs through intact guinea pig skin and various artificial membranes was then determined experimentally. It was observed that as the lecithin concentration increased from 40 to 50 and then 60% w/w in formulations, a significant decrease in KT release was obtained. A remarkable increase in the drug release was also observed in formulations containing 6.5% w/w of KT compared to those containing 1% w/w of the drug. Increasing the water content of the organogels also resulted in an increase in KT release. The optimized formulation of the organogel composed of 40% lecithin and 60% IPM (containing 0.6% w/w of water and 6.5% w/w of KT) showed the highest drug release rate. Moreover, the viscosity of different formulations and their rheological behavior were also determined. All formulations showed a slightly rheopexic behavior. It was found that an increase in lecithin concentration resulted in an increase in the viscosity of the organogel. Results have shown that KT could be incorporated at high concentrations into lecithin organogels and these systems could be considered as desirable drug delivery vehicles for water soluble drugs and are capable of providing an appropriate drug release rate and pattern.