Oil type effect on diclofenac solubilization in mixed nonionic surfactants microemulsions

Diclofenac solubilization capacity and the associated structural transitions U-type microemulsions characterized by a large continuous isotropic region were studied. The microemulsions were composed from biocompatible components that are water/sucrose laurate/ethoxylated mono-di-glyceride/oil + ethanol. The oil was R(+)-limonene or isopropylmyristate. The mixing ratios (w/w) of sucrose laurate/ethoxylated mono-di-glyceride and that of ethanol/oil equal unity. The systems were studied along the dilution line N60 (weight ratio of mixed surfactants/oil/ethanol phase equals 6/2/2) at 25 °C. Solubilization capacity of the drug was dependent on the oil type and microstructure of the microemulsion. The solubilization capacity of the drug in the reverse micelles and microemulsions was very much higher than its solubility in R(+)-limonene or isopropylmyristate. The structural transition from the water-in-oil to bicontinuous and to oil-in-water microemulsions were identified by small angle X-ray scattering and nuclear magnetic resonance measurements. Diclofenac affects the curvatures of the microstructures and consequently the limits of the structural transitions. Dilutable microemulsions are promising new diclofenac vehicles for oral intake.