Formulation of amphiphilic drug amitriptyline hydrochloride by polyoxyethylene sorbitan esters in aqueous electrolytic solution

In the present work, the interaction between an antidepressant drug amitriptyline hydrochloride and nonionic polyoxyethylene surfactants, with special attention to the possible contribution from the ion–dipole type of interaction, has been investigated by using multitechnique approach. Tensiometric and conductometric studies show steeper decrease on the critical micellar concentration gradient of the drug in the presence of electrolyte (NaCl) as well as nonionic surfactants. Critical assessments by applying Clint, Rubingh, Rosen, Motomura and other thermodynamic models confirm strong interactions in the mixed monolayer at the surface and in mixed micelle in the bulk of aqueous electrolytic solution. The structural difference in the drug and nonionic surfactants also plays a role in tuning the aggregational behavior of the drug–surfactant mixtures. Finally, it is shown by DLS measurements that the micellar growth of drug–surfactant aggregates is favored in terms of increase in hydrodynamic radii in the presence of electrolyte. However, the nonionic surfactants provide sufficient steric crowding causing dissociation of larger micelles into smaller ones with small radii.