EFFECT OF VISCOSITY INCREASING AGENT AND ELECTROLYTE CONCENTRATION ON THE RELEASE RATE OF THEOPHYLLINE FROM A HPMC BASED SUSTAINED-RELEASE CAPSULES

Sustained release (SR) granules (250-650mu) containing,theophylline were prepared using hydroxypropyl methylcellulose (HPMC) as a rate retarding polymer. The effect of variable ionic strength and viscosity increasing agent on the theophylline release rate have been investigated. Irrespective of dissolution media the theophylline release kinetics was found to be dependent on square root of time. The Higuchian release rate (K) was found to increase exponentially with the increase in ionic strength of the dissolution fluid. An opposite effect was observed with the viscosity increasing agent sodium carboxy methyl cellulose (Na-CMC) in the dissolution fluid. The release rate decreased linearly with the increase of Na-CMC concentration in the dissolution fluid.