Study of Verapamil hydrochloride release from compressed hydrophilic Polyox-Wsr tablets

This study deals with Verapamil hydrochloride release from tablets based on high molecular weight poly(ethylene oxide) (PEO). The drug release proceeds as a controlled diffusion (n=0.44-0.47), which rate is dependent on the molecular weight of PEO. Independent from it, under the conditions of the Half-change test, the drug release practically ceases after 4 h as a result of obtaining low soluble in the water base. The introduction of hydrophilic polymers with pH dependent solubility (Eudragit L, Eudispert hv and Carbopol 934) at concentrations of 10/50% with respect to PEO amount keeping constant the ratio drug: matrix insures relatively complete release both in alkali medium and under the conditions of the Half-change test. Meanwhile drug release kinetics also changes - the release of all models studied runs as a typical abnormal diffusion (a=0.66-0.87), i. e. like a diffusion-relaxation controlled process. The decrease in drug concentration leads not only to retarded release of the drug sample but also to changes in the kinetics of the process. At lower drug concentrations on the matrix from a typical abnormal diffusion it turns into a relaxation controlled diffusion (n(10%)=1).