Briefly high performance liquid chromatography (HPLC; LC- 10 AT, isocratic Shimadzu, Kyoto, Japan) furnished with SPD-10 AVP UV spectrophotometric detector (sensitivity of 0.005 absorbance units full scale; AUFS) and Lichrospher C18 column (5 m, 4.6 × 250 mm) was used to analyse ISR samples at detection wavelength of 331 nm. The mobile phase composed of acetonitrile and water (70:30 % v/v) delivered at a flow rate of 1 mL/min.16 The samples of ISR (20 L) were injected in to the column maintained at room temperature.
ISR solubility was estimated in different vehicles (oils and surfactants) according to the earlier reported method17 to screen the suitable oil, surfactant and co surfactant with highest solubility. Increasing amounts of ISR was added into the vials containing vehicles (2 mL) with agitation using cyclomixer until the precipitate of drug was observed. The sealed vials were shaken for 24 h at room temperature using orbital shaking incubator. After equilibration, samples were centrifuged at 10000 rpm for 15 min to separate undissolved drug portion. Then collected supernatant samples were analyzed for drug content using HPLC after suitable dilution with methanol. Solubility studies were conducted in triplicate and data were presented as mean ± S.D.
Preparation of self-nano emulsifying formulations (SNEFs)
Based on the highest solubility of ISR in tested vehicles, oil phase, surfactant and co-surfactant were selected and total nine combinations of self-emulsifying systems were prepared by varying oil, surfactant, co-surfactant quantities as shown in Table 1. The ratios of surfactant to co-surfactant (S/CoS ratios) mixtures studied were 1:1, 3:1 and 5:1. The constant amount of ISR (10 mg) was used in all the formulations. Briefly, ISR was dissolved in the surfactant taken in a glass vial followed by mixing of other components of the formulation i.e. oil followed by co-surfactant with vortex mixing at room temperature. The prepared SNEFs were stored in screw capped vials at room temperature until further investigation.
Construction of ternary phase diagram
Ternary phase diagram was constructed using the method reported by Craig et al. (1995)18 with slight modification to identify the stable self emulsifying regions based on the tendency to form emulsion, clarity of emulsion formed, phase separation, coalescence of droplets and drug precipitation. Briefly 0.2 mL of the prepared SNEFs were added to a beaker containing 300 mL of distilled water maintained at 37oC and the contents were mixed gently using magnetc stirrer at 100 rpm speed. Based on the tendency of emulsifaction and visual observation for phase separation, precipitation, cracking of the formed emulsion after 48 h storage at ambient temperature, self emulsifying systems were identified as stable and unstable emulsions. Spontaneous formation of clear emulsion without any signs of phase separation and drug precipitaion even after 48 h indicates...