Evaluation of thermodynamic parameters of amphiphilic tricyclic antidepressant drug imipramine hydrochloride-additive systems at the cloud point.

Cloud point (CP) of an amphiphile can be considered as the limit of its solubility as it phase separates at temperatures above the CP. The clouding components release their solvated water and separate out from the solution. In the present paper, we report the thermodynamics of clouding in amphiphilic drug, imipramine hydrochloride (IMP-a tricyclic antidepressant drug), in the presence of additives (viz., alcohols and surfactants). Surfactants are extensively used in drug delivery as drug carriers. For all cases the standard Gibbs energy change of solubilization (DeltaGs0) is evaluated and, found to be positive. However, the standard enthalpy change (DeltaHs0), and the product of standard entropy change and temperature (TDeltaSs0) values are found negative as well as positive. These values are depending upon the type and nature of the additive, and the results are discussed on the basis of these factors.