In vitro release study of diclofenac sodium from gel preparations

One-gram gel formulation each containing 30 mg of diclofenac sodium was placed on cellulose acetate membrane (pore size 0.45 μm, Sartorius, Goettingen, Germany) and fixed to one end and made water-tight with aid of a rubber band in an apparatus consisting of cylindrical tube with both ends open, with 12.1 mm inner diameter (release area = 115 mm²) as a diffusion cell. The tubes were submerged in 1000-ml vessels containing 400 ml PBS (pH 7.4) as receptor medium. The whole assembly was fixed in such a way that the lower end of the cell containing the gel just touched (1–2 mm deep) the diffusion medium. The release test was carried out at a controlled stirring rate of 100 rpm to ensure sink condition and a temperature of 37 ± 1°C by means of water jacket surrounding each cell, based on the facts that the receptor phase is in contact with the deepest skin layers and that the deep body temperature of humans is maintained between 36.2°C and 37.2°C in order to maintain the skin surface at 32°C. An aliquot of 5 mL was withdrawn at specific time intervals up to 720 min, and estimated spectrophotometrically at 276 nm. After each withdrawal, the diffusion medium was replaced with an equal volume of fresh diffusion medium. The cumulative percent release was calculated for each time (in min) interval [41, 43, 45].