The effect of hydrophilic and lipophilic polymers and fillers on the release rate of atenolol from HPMC matrices

The objective of this study is to investigate the effect of various polymers, and fillers, and their concentrations on the release rate of atenolol from polymeric matrices. Four polymers namely hydroxypropylmethylcellulose (HPMC), Eudragit RSPO, ethylcellulose (EC) and sodium carboxymethylcellulose (NaCMC) were used. The dissolution profiles showed that an increase in the concentration of HPMC and EC resulted in a reduction in the release rate of atenolol. The results indicate that it is difficult to obtain a zero-order release from the matrices containing either HPMC or EC. It is also observed that the amount of HPMC played a dominant role, affecting the drug release in binary mixtures of Eudragit-HPMC. Generally, the presence of NaCMC caused an increase in the release rate of atenolol from HPMC matrices. To determine the effect of fillers on the release rate of atenolol from HPMC matrices, lactose (a soluble filler) and dicalcium phosphate (an insoluble filler) were used. The results showed that an increase in the concentration of fillers resulted in an increase in the release rate of the drug from matrices and hydrophilicity or hydrophobicity of fillers had no significant effect on the release profile. In order to determine the mode of release, the data were analysed based on the equation Q = K (t - l)(m). Values of m were in the range of 0.32-0.99 indicating that release was controlled by both diffusion and erosion, depending on the type of polymer and concentration.