The effect of pH and Polymer type on Release of Diltiazem HCl from hydrophilic matrices

Background and

Oral administrations have been used for many years as a main method comparing to other methods. Sustained release techniques have been a great interest recently. Matrix polymers are one of the ways used to prepare a sustained-release drug and are most widely used to prepare the controlled-release drugs. Cellulose derivatives are the most common ones. Solubilities of some drugs are pH-dependent due to their acidic or basic nature. Diltiazem Hydrochloride due to having a pH-dependent solubility is a suitable model to investigate the effect of pH and also to prepare pH-independent formulations.

In the present study, an attempt was made to form pH-independent formulations using HPMC, lactose, CAP and organic acids in different ratios. The physicochemical properties of tablets prepared (including weight uniformity, hardness, tensile strength, friability and assay) were investigated. Rate of drug release was studied using USP I at pH 1.2 and 7.2, and sampling was done in the time of 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8. The drug release data were analyzed according to four kinetics models.

Drug release profile in acid free formulations showed that it was higher in the acidic medium. 50% replacement of HPMC with CAP and 1:1 ratio with drug release was pH-independent. Studying the formulations containing organic acids citric acid and polymer with 1:1 and 2:1 ratios ascorbic acid and polymer with 1:1 and 2:1 ratios and tartaric acid with 1:1 and 2:1 ratios showed their pH independent release characteristics.

These results showed the effect of combination of polymers and organic acids on drug release and its kinetic. Thus, the micro-environmental conditions for the dissolution and diffusion of diltiazem HCl were almost kept constant. The release of diltiazem HCl from tablets composed of HPMC and organic acids was found to be pH-independent.