Analysis of Tween based microemulsion in the presence of TB drug rifampicin

The purpose of present study was to formulate microemulsion composed of oleic acid + phosphate buffer (PB) + Tween 80 + ethanol and to investigate its potential as drug delivery system for an antitubercular drug rifampicin. The pseudo-ternary phase diagram has been delineated at constant surfactant/cosurfactant ratio (Km 0.55). Conductivity (σ) and viscosity (kη) studies with variation in Φ (weight fraction of aqueous phase) and ω (molar concentration ratio) show the occurrence of structural changes from water-in-oil (w/o) microemulsion to oil-in-water (o/w). Along with the solubility and partition studies of rifampicin in microemulsion components, the changes in the microstructure of the microemulsion after incorporation of drug have been evaluated using pH, σ and kη studies. The results have shown that the microemulsion remained stable after the incorporation of rifampicin (in terms of optical texture and phase separation). In addition, the particle size analysis indicates that the microemulsion changes into o/w emulsion at infinite dilution. Dissolution studies infer that a controlled release of rifampicin is expected from o/w emulsion droplet.