The sustained release of theophylline embedded in a Compritol matrix c
ontaining varying percentages of potassium chloride, hydroxypropylmeth
yl cellulose or mannitol was studied. All the formulations produced ta
blets with good mechanical properties ties. The release rate was found
to increase with the increase in the percentage of each of the three
additives used in the matrix. Approximately 20% of either potassium ch
loride or mannitol, as well as 5% hydroxypropylmethyl cellulose, could
provide the desired drug release (50% in 6 h) with the tablet remaini
ng intact. It was found that the Higuchi linear square root of time re
lationship with lag time (model 4) was the best model to describe the
drug release kinetics from tablets containing Compritol with different
additives. This also indicated that a matrix diffusion controlled mec
hanism was operative.