J.Chem.Soc.Pak., Vol. 33, No. 1, 2011 1 Design of a Microemulsion-Based Drug Delivery System for Diclofenac Sodium 1 NADEEM ABBAS KIZILBASH*, 2 SHUMAILA ASIF, 2 MOHAMMED FAIZAN NAZAR, 2 SYED SAKHAWAT SHAH AND 1 DHAIFALLAH ALENIZI 1 Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan. 2 Department of Chemistry, Hazara University, Mansehra, Pakistan. (Received on 1 st August 2009, accepted in revised form 6 th March 2010) Summary: A microemulsion-based drug delivery system has been designed for Diclofenac Sodium (DS) comprising Span 60, 1-Propanol, Water, and Lemon Oil. The microemulsion system has been characterized by a pseudo-ternary phase diagram using the water titration method. The properties and structure of this system have been studied by the use of refractive index, electrical conductivity, viscosity and UV-Visible spectroscopy. The conductivity (σ) and viscosity (kη) measurements have provided evidence for percolation behavior with variation in Φ (weight fraction of aqueous phase). This phase transition corresponds to the structural change from water-in-oil to a bicontinuous microemulsion system. The percolation threshold (ΦC) obtained from conductivity measurements was in accordance with that obtained by viscosity measurements. Five microemulsion samples were selected and the changes in microstructure after incorporation of the drug, Diclofenac Sodium (DS) were examined by centrifugation, conductivity measurements, viscosity measurements and spectroscopic studies. The conductivity measurements showed that DS-loaded samples have higher conductivity values when compared to non-loaded samples. It was also found that DS is interfacially active. In addition, loading of DS had no negative effect on the stability of the system. Introduction The objectives of this study were: (a) derivation of a pseudoternary phase diagram of the microemulsion system, (b) evaluation of the water and oil distribution in the microemulsion system using electrical conductivity and viscosity measurements, and (c) use of the prepared microemulsion system as a vehicle for the transdermal application of Diclofenac Sodium, a non- steriodal anti-inflammatory drug (NSAID). Microemulsions, as drug delivery systems, are becoming more and more important due to controlled release of drug and improved bioavailability. Microemulsions are optically trans- parent. These are low viscosity, thermodynamically stable dispersions of oil and water stabilized by surfactant, usually in combination with a co- surfactant [1-3]. Microemulsions can be different- tiated into three types’ oil-in-water, water-in-oil and bicontinuous. Microemulsion types depend on the dispersed and continuous phases [4]. The structure of microemulsion is important in drug release. Hydrophilic drugs solubilize mainly in water phase in the water-in-oil microemulsion droplets and hydrophobic drugs in oil droplets of oil-in-water microemulsions [4]. Microemulsions, as drug delivery systems, offer advantages for topical and transdermal drug delivery due to their unique properties. Some of the microemulsions advantages are their spontaneous formation, thermodynamic stability and high solubilizing capacity for various drugs. The high solubilizing capacity of microemulsion enables them to increase the solubility of many compounds particularly the solubility of hydrophobic drugs. Microemulsion systems are a useful vehicle to increase transdermal drug permeability [5]. To investigate the possibility of transdermal delivery of a drug incorporated in microemulsion system, Diclofenac Sodium was used as a model drug. The chemical structure of Diclofenac Sodium is shown in Fig. 1. Fig. 1: Chemical structure of Diclofenac Sodium. Diclofenac Sodium (DS) is a commonly used highly effective non-steriodal anti-inflammatory drug (NSAID). It is used for acute conditions of inflammation and pain, musculoskeletal disorders and arthritis [5]. Diclofenac Sodium is a relatively safe and tolerable NSAID. Serious gastrointestinal adverse effects occasionally appear after oral administration. Due to its adverse effects as well as its short biological half life, topical application of Diclofenac Sodium provides a preferred alternative to * To whom all correspondence should be addressed. GENERAL AND PHYSICAL