Formulation and Evaluation of Parenteral Sustained Release Microspheres of Diclofenac Sodium

The aim of this study was to formulate and evaluate microsphere based depot type parenteral sustained release formulation of diclofenac sodium (DFS). Drug was formulated in the form of microspheres, using varying proportion of ethylcellulose (EC) as the retardant material to extend the release, by phase separation-coacervation technique. The in vitro release pattern of the designed formulations was studied using modified Franz diffusion cell. In vivo pharmacodynamic study was carried out by determining the index of analgesia (increase in response time to thermal stress as percentage of basal response time). Tail flick method was employed to measure both the degree of analgesia and its duration of action. The prepared microspheres were white, free flowing, and spherical in shape with a mean particle size of 50 μm. In vitro release study of the micro-spheres in aqueous media was found to extend the release of DFS beyond 24 hours with DFS and EC ratio 1:3. The plot of log percentage remaining to be released vs. time gave a linear relationship indicating first-order release kinetics. The in vitro release rate constant (K_r) for different microspheres varied between 0.1448 hr^-1 and 0.0256 hr^-1. A good correlation was obtained between K, and proportion of EC in the microspheres. In vivo pharmacodynamic studies indicated that the duration of analgesic action is prolonged beyond 24 hrs in case of microsphere products of 1:3 ratio of DFS to EC, whereas administration of marketed parenteral preparation showed activity only up to 11hrs. Also, a good correlation was obtained between analgesic activity in vivo and cumulative percentage of drug release from the formulations.