Abstract:
The objective of this study was to investigate the stability of microemulsions using methyl salicylate as oil phase in the presence and the absence of hydrophobic additives and/or drug after six-month storage at ambient temperature. The investigated additives were menthol, isopropyl palmitate and isopropyl myristate. Indomethacin was as a model drug. The surfactant system of Tween 20-isopropyl alcohol (1:1) was kept constant at 50% while the dispersed phase was at 15% in which weight ratios of methyl salicylate to additive were varied. Formulations were prepared and then characterized. All samples were transparent homogenous liquids with nano-sized droplets and the O/W characteristic. After storage, all samples visually remained unchanged. The analytical results showed methyl salicylate and indomethacin were stable in the prepared microemulsions. The optimized oil phase comprised menthol as additive at a 3:1 weight ratio of methyl salicylate to menthol in the presence and the absence of indomethacin.
