Physico-chemical aspects of protein binding of nimesulide

The binding of nimesulide, a cox-2 inhibitor, to bovine serum albumin was investigated by equilibrium dialysis method at different temperatures and pH conditions. The Scatchard plots were prepared based on these drug-protein binding data. The number of binding sites (n), the value of association constant (K) at different conditions and different thermodynamic parameters (i.e., standard free energy change I”G°, standard enthalpy change I”H° and standard entropy change I”S°) of nimesulide-BSA binding were determined. The result shows that number of binding sites is around 2.5 and the value of association constant is decreasing with increasing temperature and pH. It also reveals that the value of I”G° and I”H° were highly negative and I”S° was also negative. The result indicates that the interaction between nimesulide and bovine serum albumin is exothermic and spontaneous in nature. It is postulated that nimesulide-bovine serum albumin interaction may occur due to hydrogen bond formation and ionic interaction.