Even though it is widely used, Diclofenac Sodium has a short half time it is rapidly and almost completely absorbed and 40% undergoes first-pass metabolism that lead to fluctuations in bio-availability. It also has common side effects that restrict its use such as gastric irritation gastritis, peptic ulcers and bleeding. This is the basis for designing an Extended Release (ER) dosage formulation that would maintain sustained therapeutic levels and minimise the frequency of drug administration and overcome its side effects. Meanwhile, the extended release Diclofenac Sodium tablet formulation is supplied as or contained in medications under a variety of trade names that may not be bio-equivalent. In-vivo testing is applied to measure the active ingredient in the blood supply using High-Performance Liquid Chromatography (HPLC) methods with ultraviolet because it is sensitive, simple, rapid and economic. Animal models such as beagle dogs are preferred because they feasible and less costly.