Mechanism of synergistic interactions and its influence on drug release from extended release matrices manufactured using binary mixtures of polyethylene oxide and sodium carboxymethylcellulose

The ability of anionic polymer sodium carboxymethylcellulose to influence the release of four model cationic drugs (chlorpheniramine maleate, venlafaxine hydrochloride, propranolol hydrochloride and verapamil hydrochloride) from extended release (ER) hydrophilic matrices based on non-ionic polymer polyethylene oxide was investigated by X-ray photoelectron spectroscopy (XPS), isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). For all studied APIs, a combination of polyethylene oxide with sodium carboxymethylcellulose produced slower drug release compared to the matrices of single polymers. This behaviour was mainly attributed to the interaction of ester/carboxylic acid functionalities to yield H-bonding between the anionic polymer groups and the additionally protonated N-atoms of the active substances. X-ray photoelectron and isothermal titration calorimetry studies confirmed drug–polymer interaction and polymer–polymer interaction (i.e. the PEO binding with negatively charged NaCMC), whilst differential scanning calorimetry indicated the existence of both crystalline and molecularly dispersed active forms in the created complexes. The drug release mechanisms were fitted to various models suggesting diffusion control for the majority of the formulations. The Korsmeyer–Peppas model was found to be the most suitable for description of release profiles of all formulations. The present study showed that XPS and ITC in combination with DSC can be valuable tool to investigate the presence and nature (mechanism) of synergistic interactions between polymers and drugs in extended release matrix tablets.