PREPARATION CHARACTERIZATION AND EVALUATION OF CROSS LINKED STARCH UREA - A MODIFIED STARCH AS RATE CONTROLLING POLYMER FOR SUSTAINED RELEASE FLOATING TABLETS

The objective of the present study is to prepare, characterize and to evaluate a new modified starch namely cross linked starch urea for its application in the formulation of sustained release floating tablets as rate controlling polymer. Cross linked starch urea was prepared and characterized by various physical properties and IR spectra. Sustained release floating tablets of three anti-hypertensive drugs namely Captopril, Losartan and Valsartan were formulated employing cross Linked starch Urea as rate controlling polymer and were evaluated. Cross linked starch urea prepared by gelatinizing potato starch in the presence of urea and calcium chloride was insoluble in water and aqueous fluids of acidic and alkaline pHs. Cross linked starch urea exhibited good swelling in water. The swelling index was 630.2%. As crosslinked starch urea is insoluble and has good swelling in water, it is considered suitable as release retarding and rate controlling matrix polymer for sustained release floating tablets. stained release tablets of (i)captopril, (ii) losartan and (iii) valsartan prepared using cross linked starch urea as matrix polymer were non disintegrating in water, acidic (pH 1.2) and alkaline ( pH 7.4) fluids and gave slow and controlled release over longer periods of time. In each case the release rate depended on the strength or concentration of cross linked starch urea polymer in the tablets. A good linear relationship was observed between percent polymer in the matrix tablets and release rate (K0) with all the three drugs indicating that the cross linked starch urea polymer is an efficient rate controlling polymer suitable for design of sustained release tablets. Drug release from these SR tablets was by diffusion mechanism, fickian diffusion in the case of tablets containing low percent of polymer and non fickian (anamalous) diffusion in the case of tablets containing high percent of polymer. Cross linked starch urea alone and in combination with sodium bicarbonate (gas generating agent) was found not suitable for formulation of floating tablets though it has good rate controlling effect for formulation of sustained release tablets. When cross linked starch urea was used along with bees wax (lipohilic polymer) and starch acetate (good film forming polymer) it was found suitable for formulation of floating tablets. Floating tablets formulated with cross linked starch urea (50%) as matrix polymer, Bees wax (5%) and starch acetate (5%) as floating enhancers and sodium bicarbonate as gas generating agent exhibited good floating over 13 – 14 hrs with a floating lag time of 45 – 60 seconds. Drug release from these floating tablets was spread over 12 hrs with all the three drugs studied. The drug release from these tablets was by non fickian (anomalous) diffusion. Thus cross linked starch urea was found to be a good rate controlling polymer for sustained release tablets and along with bees wax and starch acetate it was also a good matrix polymer for floating tablets. Key words: Cross linked starch urea, Sustained release floating tablets, Rate controlling polymer, Captopril, Losartan, Valsartan