Lecithin - Stabilized Microemulsion: An Organogel for Topical Application of Ketorolac Tromethamine. I: Phase Behavior Studies

The partial phase behavior of systems composed of lecithin/isopropyl myristate (IPM)/water or ketorolac tromethamine (KT) solutions (2.5, 5, 10 and 50% w/w) at various lecithin/IPM weight ratios (km) have been investigated by the construction of phase diagrams. A commercially available soybean lecithin (namely, Epikuron 200, phosphatidylcholine purity greater than 95%) was used in this study. Phase diagrams showed a narrow area of existence of a non-birefringent, transparent isotropic region along the lecithin / IPM axis in all systems, regardless of the km. The isotropic regions were stable for a minimum of 3 months at room temperature. The surfactant/oil ratio required for maximum KT incorporation has its minimum value in systems prepared with 50% KT solution, whereas the maximum value is obtained when a 2.5% KT solution was incorporated into the gel matrix. The results have also showed that for a given system, as km increases, the incorporation capacity increases. No significant differences in phase behavior were noted when altering the concentration of KT solution from 2.5 – 10%. However, a small decrease in the extent of the gel region was observed when 50% drug solution was incorporated into the system.