A Controlled porosity of the membrane is accomplished by the use of pore former. The usual dose of glimepiride was 4 mg to be taken twice daily. The plasma half life of glimepiride was 5 h. Hence, glimepiride was chosen as a model drug with an aim to develop a controlled release system for 24 h. Sodium chloride was use as osmogent. Cellulose acetate was used as the semi permeable membrane. The porous osmotic pump contains pore forming water-soluble additive (Poly ethylene glycol 400) in the coating membrane which after coming in contact with water, dissolve, resulting in an in situ formation of microporous structure. The effect of different formulation variables, namely, ratio of drug to osmogent, membrane weight gain and concentration of pore former on the in vitro release was studied using 23 full factorial design. The effect of pH and agitation intensity on drug release was also studied. It was found that drug release rate increased with the amount of osmogent because of increased water uptake. Drug release was inversely proportional to membrane weight gain. Surface plot is also presented to graphically represent the effect of independent variables on t90. Optimized formulation was found to release above 90% of glimepiride at a zero order rate for 24 h
