Thermodynamic, interfacial and hydrodynamic aspects of interaction of cationic drug amitriptyline hydrochloride with anionic and nonionic polymers

Abstract

Interaction of amitriptyline hydrochloride (AMT), a tricyclic antidepressant amphiphilic drug, was seen with various polymers using conductometry, surface tensiometry and viscometry. Amphiphilic drug interacted with polymers in a surfactant like fashion. The plots of specific conductivity versus concentration of drug were nonlinear with three different linear regions and with two clear breaks. First break point, i.e., critical aggregation concentration (C1), appeared well below the usual critical micelle concentration while polymer domain saturated at quite higher concentration (C2). In case of surface tension measurements, the isotherms were composed of three identifiable points termed as T1, T2 and T3. T1 signaled the onset of the interaction, i.e., C1, while T2 is regarded as the saturation of the polymer backbone. For weakly interacting polymers the surface tension isotherms were different from the strongly interacting polymers. Viscosity measurements suggest the relative size of the polymer-drug complex which changes differently for each polymer according to their nature of interactions. Free energies of aggregation (∆Gagg) and micellization (∆Gmic) were computed with the help of degrees of micelle ionization obtained from the specific conductivity — [AMT] plots.