Design and in vitro evaluation of acyclovir sustained release tablet using hydrophilic matrix system

Abstract

To design an oral acyclovir sustained release tablet. The use of four hydrophilic polymers, hydroxypropyl methylcellulose, xanthan gum, sodium alginate and carbopol 934P, as matrix forming agents was evaluated. Sustained release of acyclovir was achieved from hydroxypropyl methycellulose, xanthan gum and sodium alginate containing matrices, whereas carbopol 934P did not produce sustained release property. The following factors that might influence drug release were also investigated : amount of polymer, type of diluent, pH and ionic strength of dissolution medium. An increase in amount of polymer led to a decrease in drug release rate. Nevertheless, the stronger gel layer around the matrices and low solubilities of the drug and the diluent might play a more important role for controlling drug release from the matrices and thus obscured the effect of the amount of polymer on drug release rate. The effect of type of diluent on drug release rate depended on amount and solubility of the diluent in the dissolution medium. The strong influence of pH of dissolution medium on drug release rate of HPMC and xanthan gum containing matrices was observed. The differences in strength of the gel barrier and drug solubilities in media with different pH values could be attributed to this finding. In case of sodium alginate martrices, the difference in pH value of dissolution medium gave the different patterns of drug release profile and also drug release mechanisms due to the pH dependent solubility of the polymer. The ionic strength of dissolution medium also affected the drug release rate. The stronger gel layer around the matrices corresponded well with the increased ionic strength of dissolution medium, resulting in the slower drug release rate. The difference in drug release characteristics could be explained in terms of the differences in swelling and erosion behaviors of the matrices. The dependence of drug release mechanism on the compositions of the matrices and the conditions of dissolution medium could be noted. Both diffusion and matrix erosion controlled the drug release from the matrices.