RELEASE OF PROPRANOLOL HYDROCHLORIDE FROM MATRIX TABLETS CONTAINING HYDROXYPROPYLMETHYLCELLULOSE K4M AND CARBOPOL-974

The release of propranolol hydrochloride from matrices containing hydroxypropylmethylcellulose and carbopol has been examined at different ratios of the polymers. Similar dissolution rates were found from the data corresponding to 5-35% of total drug release from matrices containing the same weight of polymer, but a burst release occurred from formulations containing 1: > 3 HPMC/carbopol once 35% of the drug had dissolved. In order to explain these results, studies on cloud points, water distribution, hydration and viscosity were carried out. Mixtures of both polymers resulted in a decrease in the values of the cloud points. Increased quantities of free water in the gels were apparent, producing a reduction in viscosity. Hydration studies, determined by DSC, on carbopol gels and matrices indicated that two different types of water were present in the scans of melting process. Additionally, the amount of water imbibed for this polymer was lower than that by HPMC or 1:1 mixture of the polymers. The burst release, during dissolution, may be explained by the formation of a complex between propranolol and carbopol.