The paper focuses on the study of the effect of pH of dissolution medium on the release of diltiazem hydrochloride from carbomeric matrices. Swelling of carbomers, high-molecular cross-linked anionic polymers, is dependent on the value of pH, which decides whether these polymers exist in an ionized or a non-ionized form. In alkaline medium, carboxylic groups of carbomers ionize and hydrate markedly, which also facilitates their interaction with cationic drugs, in this case with diltiazem hydrochloride. The development of a sparingly soluble complex drug-polymer, the presence of which was demonstrated with the use of Fourier IR spectrophotometry, is one of the factors which causes decelerated release of the drug as well as decreased swelling of matrices in this dissolution medium. In both selected dissolution media, an assumption has been confirmed that with an increasing concentration of the polymer in the system a smaller share of the drug is released. Drug release from matrix tablets is also influenced by the rate of dissolution of the drug in dependence on the pH of the medium. Being a salt of a feeble base and a strong acid, diltiazem hydrochloride is more slowly soluble in an alkaline medium than in the medium with pH 1.2. This factor also contributes to its slower release in the medium of phosphate buffer of pH 7.4.

        Key words: Carbopol 974P – controlled release – drug-polymer interaction – effect of pH – diltiazem hydrochloride