A novel therapeutic deep eutectic solvent (THEDES) of thioacetazone (TAZ) with polyethylene glycol 400 (PEG) of stoichiometry 1:8 was obtained by heating with stirring method. The interactions between the components that constitute the THEDES were studied by proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier-transform infrared spectroscopy (FT-IR), confirming that the stable eutectic system is formed by H-bonds between drug and polymer. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods were used to characterize the thermal behavior of THEDES. It was found that the melting point of THEDES is -22.3 °C, which is lower than the melting points of the phase-forming components. The temperature dependences of the density and viscosity of the obtained eutectic system were measured. It was found that the values of these physical parameters meet the requirements for creating pharmaceutical dosage forms. The comparative analysis of the dissolution behavior of TAZ in solid and liquid forms in water at 37 оC was carried out. Dissolution of the obtained THEDES in water demonstrated a supersaturation phenomenon, characterized by a rapid increase in the content of the active pharmaceutical substance in the solution, and then a reducing of drug concentration to equilibrium values. The maximum concentration of the eutectic system of TAZ in an aqueous solution is 26.6 times higher than the aqueous solubility of the drug. Whereas, the thermodynamic solubility of the prepared liquid form of drug compared to the crystalline one, increases by 13.3 times. The experimentally determined partition coefficient of THEDES in the 1-octanol/water system equal to 1.97 indicates the TAZ lipophilicity increasing in the eutectic composition. As a result, the formation of a deep eutectic system of TAZ with PEG demonstrates great potential for creating a new delivery system for this drug with improved bioavailability.
