The role of various surfactants and fillers in controlling the release rate of theophylline from HPMC matrices

The effect of lactose, NaCMC and various surfactants, i.e. sodium lauryl sulfate, cetyltriammonium bromide, Arlacel 60 and Tween 80 on the release rate of theophylline from HPMC matrices was evaluated. The results showed that an increase in the concentration of lactose or NaCMC resulted in an increase in the release rate. Results concerning the effect of surfactants on the release rate showed that incorporating sodium lauryl sulfate into HPMC matrices increased the release rate. Different results were obtained for the other surfactants. The effects of filler and surfactants on the release kinetics were also investigated. The results showed that a reduction in the ratio of HPMC to NaCMC resulted in a reduction in the n value (indicative of the mechanism of release in Higuchi's equations). The presence of sodium lauryl sulfate caused a reduction in the n values from 0.75 (without surfactant) to 0.591 (10 w/w sodium lauryl sulfate), indicating that the contribution of erosion fell as the concentration of sodium lauryl sulfate rose.