THE INFLUENCE OF ADDITIVES ON THE CLOUD POINT, DISINTEGRATION AND DISSOLUTION OF HYDROXYPROPYLMETHYLCELLULOSE GELS AND MATRIX TABLETS

The ability of a salt to lower the cloud point of hydroxypropylmethylcellulose (HPMC) gels was found to follow their order in the lyotropic series, i.e. chloride < tartrate < phosphates and potassium < sodium. Anions were more important than cations in lowering the cloud point. The dissolution of propranolol hydrochloride from HPMC matrix tablets into dissolution media containing a number of different phosphate and chloride salts was investigated. As the ionic strength increased the dissolution rates decreased to a minimum before rising to give a 'burst' release. Disintegration times of HPMC matrices, without active, also varied to the ionic strength of the disintegration medium. By determining the cloud points it proved possible to predict if a matrix will show burst release in a given solution of electrolytes. Propranolol hydrochloride, promethazine hydrochloride, aminophylline and tetracycline hydrochloride increased the cloud point but theophylline and quinine bisulphate had little effect on the cloud point.