Effect of Formulation Variables on Phenobarbital Release from HPMC Matrices

Controlled release sweljable tablets of phenobarbital were prepared by a simpledirect compression process using hydroxypropyl methylcellulose (hpmc) as thematrix former, the effects of the viscosity grades of hpmc and hpmcllactose ratioand ethylcellulose (ec)/sodium carboxymethylcellulose (nacmc) and theirconcentrations on the release behavior of phenobarbital from hpmc matrices wereinvestigated. in order to determine the mode of release, the data were analyzed basedon the equation q= k t. higher drug release rate was found for formulations withlower hpmc/lactose ratios and lower hpmc viscosity grades . the viscosity ofhpmc polymer has a large influence on the erosion rate of matrix tablet. use oflow viscosity grade of hpmc polymer is desired for drugs that are poorly watersoluble such as phenobarbital since the erosion rate of tablet matrix is the controllingfactor for drug release. as the proportion ofec or nacmc in admixture with hpmcincreased, the release rates gradually increased. it is also observed that the amountof hpmc played a dominant role, affecting the drug release in binary mixtures. invitro release studies demonstrated that use of an appropriate blend of hpmc andbc or nacmc enables to better control of drug release profiles and approach to zeroorder kinetic.