Oxazepam dissolution rate from hydroxypropylmethylcellulose matrices

The effect of some formulation variables on the release rate of oxazepam from hydroxypropylmethylcellulose (HPMC) has been investigated. The principal factors affecting this parameter were the content and molecular weight of HPMC, and the drug particle size. pH modified the oxazepam solubility; however, the liberation mechanism was not affected. The oxazepam release mechanism from these matrices has been examined. Values of the diffusional exponent n were in the range 0.61-0.74, indicating that the release of drug was controlled by both diffusion and erosion. When the tablets contained 30% HPMC K100 and the oxazepam particle size was 0.210-0.250 mm, near-zero-order kinetics was obtained (n = 0.85), indicating that erosion plays an important role in the oxazepam liberation.