Biomolecules, nicotinamide (NA), and khellin (KH) have been used orally for a number of diseases for the last few decades. NA is shown as an HIV, Mycobaterium tuberculosis, and pellagra preventive agent, whereas KH is used in renal colic, diuretic, kidney stone, coronary, bronchial asthma, angina, vitiligo, and psoriasis. In recent years, research on solid dispersions of binary drug products is playing a significant role in the drug delivery process of the pharmaceutical industries. The present study highlights the thermodynamic characteristics of solid dispersions binary products of active pharmaceutical ingredient KH with pharmaceutical excipient NA. These products have been prepared through melting/fusion method. The solid-liquid equilibrium (SLE) data of NA-KH system favors the formation of an eutectic (E) at 0.135 mole fraction of KH and melting temperature 120.6 degrees C and noneutectic solid dispersions (A1-A8) at their defined compositions and temperatures. To illustrate the molecular interaction, the activity coefficient model based on enthalpy of fusion is employed to calculate the excess partial and integral thermodynamic functions such as g(E), h(E), and s(E). The positive value of excess Gibbs free energy predicts the stronger molecular interaction between the like molecules as compared to unlike molecules. The spontaneity of mixing of eutectic and noneutectic alloys was discussed by the integral mixing quantities G(M), H-M, and S-M. The value of critical radius (r*) of solid dispersions is found in nanometer (nm) scale, which suggests the process of solidification for nanosolid dispersions, and it is very surprising for the pharma world. The binary interface structure of alloys has been discussed in light of the Jackson model of interface structure.